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{{short description|Outcrop of rock in the sea formed by the growth and deposit of stony coral skeletons}} | |||
{{ocean habitat topics|image=Blue Linckia Starfish.JPG|thumb|caption=] of a coral reef}} | |||
{{pp-semi-indef}} | |||
{{use British English|date=August 2021}} | |||
{{use dmy dates|date=August 2021}} | |||
] of a coral reef|thumb]] | |||
'''Coral reefs''' are underwater structures made from ] secreted by ]s. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from ]s, which in turn consist of ]s that cluster in groups. The polyps are like tiny ]s, to which they are closely related. Unlike sea anemones, coral polyps secrete hard carbonate ]s which support and protect their bodies. Reefs grow best in warm, shallow, clear, sunny and agitated waters. | |||
{{Ocean habitat topics}} | |||
A '''coral reef''' is an underwater ] characterized by reef-building ]s. Reefs are formed of ] of ] ]s held together by ].<ref>{{Cite web|url=https://coral.org/en/coral-reefs-101/how-reefs-are-made/|title=How Reefs Are Made|date=2021|website=Coral Reef Alliance|url-status=live|archive-url=https://web.archive.org/web/20211030053454/https://coral.org/en/coral-reefs-101/how-reefs-are-made/|archive-date=30 October 2021|access-date=19 April 2022}}</ref> Most coral reefs are built from ]s, whose polyps cluster in groups. | |||
Coral belongs to the ] ] in the animal ] ], which includes ]s and ]. Unlike sea anemones, corals secrete hard carbonate ]s that support and protect the coral. Most reefs grow best in warm, shallow, clear, sunny and agitated water. Coral reefs first appeared 485 million years ago, at the dawn of the ], displacing the microbial and ] reefs of the ].<ref>{{cite journal |last1=Lee |first1=Jeong-Hyun |last2=Chen |first2=Jitao |last3=Chough |first3=Sung Kwun |title=The middle–late Cambrian reef transition and related geological events: A review and new view |journal=Earth-Science Reviews |date=1 June 2015 |volume=145 |pages=66–84 |doi=10.1016/j.earscirev.2015.03.002 |bibcode=2015ESRv..145...66L |issn=0012-8252}}</ref> | |||
Often called “rainforests of the sea”, coral reefs form some of the most diverse ]s on Earth. They occupy less than 0.1% of the world's ocean surface, about half the area of France, yet they provide a home for 25% of all marine ],<ref>Spalding MD and Grenfell AM (1997) '''Coral Reefs'', '''16''' (4):225–230. {{doi|10.1007/s003380050078}}</ref><ref name="Spalding" /><ref name=Mulhall>Mulhall M (2007) Duke Environmental Law and Policy Forum '''19''':321–351.</ref> | |||
including ], ]s, ]s, ], ]s, ]s, ]s and other ].<ref>{{cite book | |||
|title=Hawai{{okina}}i's Sea Creatures | |||
|last=Hoover |first=John | |||
|isbn=15854702902 {{Please check ISBN|reason=Invalid length.}} | |||
|publisher=Mutual | |||
|date=November, 2007}}</ref> | |||
], coral reefs flourish even though they are surrounded by ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but ] and cold water corals also exist on smaller scales in other areas. | |||
Sometimes called ''rainforests of the sea'',<ref> {{Webarchive|url=https://web.archive.org/web/20100210050558/https://oceanservice.noaa.gov/oceans/corals/ |date=10 February 2010 }} ''NOAA National Ocean Service''. Accessed: 10 January 2020.</ref> shallow coral reefs form some of Earth's most diverse ecosystems. They occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine ],<ref>{{cite journal|vauthors=Spalding MD, Grenfell AM |doi=10.1007/s003380050078| title=New estimates of global and regional coral reef areas| year=1997| journal=Coral Reefs| volume=16| issue=4| pages=225–230 |bibcode=1997CorRe..16..225S |s2cid=46114284}}</ref><ref name="Spalding"/><ref name="Mulhall">{{cite journal|last1=Mulhall|first1= M. |date=Spring 2009|url=http://www.law.duke.edu/shell/cite.pl?19+Duke+Envtl.+L.+&+Pol%27y+F.+321+pdf |title=Saving rainforests of the sea: An analysis of international efforts to conserve coral reefs |archive-url=https://web.archive.org/web/20100106053233/http://www.law.duke.edu/shell/cite.pl?19+Duke+Envtl.+L.+&+Pol%27y+F.+321+pdf |archive-date=6 January 2010|journal=Duke Environmental Law and Policy Forum |volume=19|pages=321–351}}</ref><ref>{{cite web|title=Where are Corals Found? |url=http://coralreef.noaa.gov/aboutcorals/coral101/corallocations/|website=NOAA Coral Reef Conservation Program|publisher=]|date=13 May 2011|access-date=24 March 2015|url-status=dead<!--Maybe this will work when Internet Archive is not fund raising-->|archive-date=2016-03-04|archive-url= https://web.archive.org/web/20160304053758/http://coralreef.noaa.gov/aboutcorals/coral101/corallocations/ }}</ref> including ], ]s, ]s, ], ]s, ]s, ]s and other ].<ref>{{cite book |url={{google books |plainurl=y |id=TxrHBCs1u4EC}}|title=Hawaiʻi's Sea Creatures |last=Hoover |first=John |isbn=978-1-56647-220-3 |publisher=Mutual |date=November 2007}}</ref> Coral reefs flourish in ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but ] and cold water coral reefs exist on smaller scales in other areas. | |||
Coral reefs deliver ] to tourism, fisheries and ]. The annual global economic value of coral reefs has been estimated at $US375 billion. However, coral reefs are fragile ecosystems, partly because they are very sensitive to water temperature. They are under threat from ], ], ], ] for ], overuse of reef resources, and harmful land-use practices, including urban and ] and ], which can harm reefs by encouraging excess ] growth.<ref name="Corals reveal impact of land use">{{cite web| url=http://www.coralcoe.org.au/news_stories/landimpacts.html | title= Corals reveal impact of land use | accessdate = 12 July 2007 | publisher=ARC Centre of Excellence for Coral Reef Studies}}</ref><ref>{{cite web | |||
|url=http://www.hcri.ssri.hawaii.edu/files/media/pr-water_quality.pdf | |||
Shallow tropical coral reefs have declined by 50% since 1950, partly because they are sensitive to water conditions.<ref>{{Cite web |first=Patrick |last=Greenfield |date=2021-09-17|title=Global coral cover has fallen by half since 1950s, analysis finds |url=https://www.theguardian.com/environment/2021/sep/17/global-coral-cover-halves-since-1950s-analysis-finds-aoe|access-date=2021-09-18|website=The Guardian}}</ref> They are under threat from ] (nitrogen and phosphorus), rising ] and ], overfishing (e.g., from ], ], ] on ]), sunscreen use,<ref name="Sunscreen">{{cite journal |last1=Danovaro|first1=Roberto|last2=Bongiorni|first2=Lucia|last3=Corinaldesi|first3=Cinzia |last4=Giovannelli|first4=Donato|last5=Damiani|first5=Elisabetta|last6=Astolfi |first6=Paola|last7=Greci |first7=Lucedio|last8=Pusceddu|first8=Antonio|date=April 2008|title=Sunscreens Cause Coral Bleaching by Promoting Viral Infections|journal=Environmental Health Perspectives|volume=116|issue=4 |pages=441–447 |doi=10.1289/ehp.10966|pmc=2291018|pmid=18414624}}</ref> and harmful land-use practices, including ] and seeps (e.g., from ]s and cesspools).<ref name="Corals reveal impact of land use">{{cite web|title=Corals reveal impact of land use |url=http://www.uq.edu.au/news/?article=12183|access-date=September 21, 2013|publisher=ARC Centre of Excellence for Coral Reef Studies}}</ref><ref>{{cite web|last=Minato|first=Charissa|date=July 1, 2002 |title=Urban runoff and coastal water quality being researched for effects on coral reefs |url=http://www.hcri.ssri.hawaii.edu/files/media/pr-water_quality.pdf|url-status=dead|archive-url=https://web.archive.org/web/20100610170312/http://www.hcri.ssri.hawaii.edu/files/media/pr-water_quality.pdf|archive-date=June 10, 2010}}</ref><ref>{{cite web |date=July 1998 |title=Coastal Watershed Factsheets – Coral Reefs and Your Coastal Watershed |publisher=Environmental Protection Agency Office of Water |url=http://water.epa.gov/type/oceb/fact4.cfm |url-status=dead |archive-date=2010-08-30 |archive-url=https://web.archive.org/web/20100830153311/http://water.epa.gov/type/oceb/fact4.cfm}}</ref> | |||
|title=Urban runoff and coastal water quality being researched for effects on coral reefs | |||
|first=Charissa |last=Minato | |||
Coral reefs deliver ] for tourism, fisheries and ]. The annual global economic value of coral reefs has been estimated at anywhere from US$30–375 billion (1997 and 2003 estimates)<ref name="Cesar" /><ref name="Costanza" /> to US$2.7 trillion (a 2020 estimate)<ref>{{Cite web|title=The Sixth Status of Corals of the World: 2020 Report|website=GCRMN |url=https://gcrmn.net/2020-report/ |access-date=2021-10-05}}</ref> to US$9.9 trillion (a 2014 estimate).<ref>{{cite journal |last1=Costanza |first1=Robert |last2=de Groot |first2=Rudolph |last3=Sutton |first3=Paul |title=Changes in the global value of ecosystem services |journal=Global Environmental Change |date=2014 |volume=26 |issue=1 |pages=152–158 |doi=10.1016/j.gloenvcha.2014.04.002|bibcode=2014GEC....26..152C |s2cid=15215236 |url=https://discovery.ucl.ac.uk/id/eprint/10189453/ }}</ref> | |||
|date=July 1, 2002 | |||
|accessdate=December, 2010}}</ref><ref>{{cite web | |||
Though the shallow water tropical coral reefs are best known, there are also deeper water reef-forming corals, which live in colder water and in temperate seas. | |||
|url=http://water.epa.gov/type/oceb/fact4.cfm | |||
|title=Coastal Watershed Factsheets – Coral Reefs and Your Coastal Watershed | |||
|publisher=Environmental Protection Agency Office of Water | |||
|epa= 842-F-98-008 | |||
|date=July 1998 | |||
|accessdate=December, 2010}}</ref> | |||
{{toclimit|2}} | |||
== Formation == | == Formation == | ||
{{ |
{{Further|Atoll|Fringing reef|The Structure and Distribution of Coral Reefs}} | ||
Most coral reefs were formed after the ] when melting ice caused |
Most coral reefs were formed after the ] when melting ice caused ] to rise and flood ]. Most coral reefs are less than 10,000 years old. As communities established themselves, the reefs grew upwards, pacing rising ]s. Reefs that rose too slowly could become drowned, without sufficient light.<ref>{{cite web |url=http://www.eoearth.org/article/Coral_reef#Types_of_Coral_Reefs |title=Coral reef |last=Kleypas |first=Joanie |date=2010 |website=The Encyclopedia of Earth |archive-url=https://web.archive.org/web/20100815052312/http://www.eoearth.org/article/Coral_reef |archive-date=August 15, 2010 |url-status=dead |access-date=April 4, 2011}}</ref> Coral reefs are also found in the deep sea away from ], around ] and ]s. The majority of these islands are ] in origin. Others have ] origins where ] lifted the deep ocean floor. | ||
In '']'',<ref name="The structure and distribution of coral reefs">{{cite book|last=Darwin|first=Charles R.|title=The Structure and Distribution of Coral Reefs. Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836.|year=1842|publisher=Smith Elder and Co.|location=London |url=http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F271&pageseq=1}} </ref> ] set out his theory of the formation of atoll reefs, an idea he conceived during the ]. He theorized that ] and ] of Earth's ] under the oceans formed the atolls.<ref name=cr>{{Cite web|url=http://darwin-online.org.uk/EditorialIntroductions/Chancellor_CoralReefs.html |title=Introduction to ''Coral reefs'' |author=Chancellor, Gordon |year=2008 |publisher=Darwin Online |access-date=January 20, 2009}}</ref> Darwin set out a sequence of three stages in atoll formation. A ] forms around an extinct ] as the island and ocean floor subside. As the subsidence continues, the fringing reef becomes a barrier reef and ultimately an atoll reef. | |||
In 1842 in his first ], '']''<ref>{{Cite document | |||
| last= Darwin | |||
| first= Charles | |||
| year = 1842 | |||
| title =The Structure and Distribution of Coral Reefs. Being the first part of the geology of the voyage of the Beagle, under the command of Capt. Fitzroy, R.N. during the years 1832 to 1836 | |||
| publication-place = London | |||
| publisher =Smith Elder and Co | |||
| url =http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F271&pageseq=1}}</ref> ] set out his theory of the formation of ]s, an idea he conceived during the ]. He theorized ] and ] of the Earth's ] under the oceans formed the atolls.<ref name=cr>{{Cite document|url=http://darwin-online.org.uk/EditorialIntroductions/Chancellor_CoralReefs.html |title=Introduction to Coral reefs |author=Gordon Chancellor |year=2008 |publisher=Darwin Online |accessdate=2009-01-20}}</ref> Darwin’s theory sets out a sequence of three stages in atoll formation. It starts with a ] forming around an extinct ] as the island and ocean floor subsides. As the subsidence continues, the fringing reef becomes a barrier reef, and ultimately an ]. | |||
<gallery> | <gallery widths="120" heights="80"> | ||
File:Atoll forming-volcano.png|Darwin’s theory starts with a ] which becomes extinct | |||
File:Atoll forming-volcano.png|Darwin's theory starts with a ] which becomes extinct | |||
File:Atoll forming-Fringing reef.png|As the island and ocean floor subside, coral growth builds a ], often including a shallow lagoon between the land and the main reef. | File:Atoll forming-Fringing reef.png|As the island and ocean floor subside, coral growth builds a ], often including a shallow lagoon between the land and the main reef. | ||
File:Atoll forming-Barrier reef.png|As the subsidence continues, the fringing reef becomes a larger barrier reef further from the shore with a bigger and deeper ] inside. | File:Atoll forming-Barrier reef.png|As the subsidence continues, the fringing reef becomes a larger barrier reef further from the shore with a bigger and deeper ] inside. | ||
Line 47: | Line 33: | ||
</gallery> | </gallery> | ||
Darwin predicted that underneath each lagoon would be a ] base, the remains of the original volcano. Subsequent |
Darwin predicted that underneath each ] would be a ] base, the remains of the original volcano.<ref>{{Cite web|date=2017-03-11|title=4 Main Theories of Coral Reefs and Atolls/Oceans/Geography|url=https://www.geographynotes.com/oceans/4-main-theories-of-coral-reefs-and-atolls-oceans-geography/2704|access-date=2020-08-01|website=Geography Notes|language=en-US}}</ref> Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the ] where the water is agitated, but can only live within a limited depth range, starting just below low ]. Where the level of the underlying earth allows, the corals grow around the coast to form fringing reefs, and can eventually grow to become a barrier reef. | ||
] Ocean Education Service. Retrieved |
{{Webarchive|url=https://web.archive.org/web/20120714035333/http://oceanservice.noaa.gov/education/kits/corals/media/supp_coral04a.html |date=July 14, 2012 }} ] Ocean Education Service. Retrieved January 9, 2010.</ref>]] | ||
Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies |
Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides slowly, the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land. A barrier reef can encircle an island, and once the island sinks below sea level a roughly circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not usually form complete circles but are broken in places by storms. Like ], a rapidly subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called ''coral drowning''.<ref name="Webster Coral subsidence">{{cite journal|last=Webster|first=Jody M. |author2=Braga, Juan Carlos |author3=Clague, David A. |author4=Gallup, Christina |author5=Hein, James R. |author6=Potts, Donald C. |author7=Renema, Willem |author8=Riding, Robert |author9=Riker-Coleman, Kristin |author10=Silver, Eli |author11=Wallace, Laura M. |title=Coral reef evolution on rapidly subsiding margins|journal=Global and Planetary Change|date=1 March 2009 |volume=66 |issue=1–2|pages=129–148|doi=10.1016/j.gloplacha.2008.07.010 |bibcode=2009GPC....66..129W}}</ref> Corals that rely on ] can die when the water becomes too deep for their ] to adequately ], due to decreased light exposure.<ref name="Webster coral drowning">{{cite journal|last=Webster|first=Jody M. |author2=Clague, David A. |author3=Riker-Coleman, Kristin |author4=Gallup, Christina |author5=Braga, Juan C. |author6=Potts, Donald |author7=Moore, James G. |author8=Winterer, Edward L. |author9=Paull, Charles K. |title=Drowning of the −150 m reef off Hawaii: A casualty of global meltwater pulse 1A?|journal=Geology|date=1 January 2004|volume=32|issue=3|page=249 |doi=10.1130/G20170.1 |bibcode=2004Geo....32..249W}}</ref> | ||
The two main variables determining the ], or shape, of coral reefs are the nature of the |
The two main variables determining the ], or shape, of coral reefs are the nature of the ] on which they rest, and the history of the change in sea level relative to that substrate. | ||
The approximately 20,000 |
The approximately 20,000-year-old ] offers an example of how coral reefs formed on continental shelves. Sea level was then {{convert|120|m|ft|abbr=on}} lower than in the 21st century.<ref>{{cite report |year=2006 |title=Reef Facts for Tour Guides: A "big picture" view of the Great Barrier Reef |url=http://www.gbrmpa.gov.au/__data/assets/pdf_file/0017/12437/Reef-Facts-01.pdf |access-date=June 18, 2007 |publisher=Great Barrier Reef Marine Park Authority |url-status=dead |archive-url=https://web.archive.org/web/20070620013057/http://www.gbrmpa.gov.au/__data/assets/pdf_file/0017/12437/Reef-Facts-01.pdf |archive-date=June 20, 2007}}</ref><ref name="AIMSage">{{cite web |last=Tobin |first=Barry |title=How the Great Barrier Reef was formed |publisher=Australian Institute of Marine Science |orig-year=1998 |year=2003 |url=http://www.aims.gov.au/pages/research/project-net/reefs/apnet-reefs00.html |access-date=November 22, 2006 |url-status=dead |archive-date=October 5, 2006 |archive-url=https://web.archive.org/web/20061005122324/http://www.aims.gov.au/pages/research/project-net/reefs/apnet-reefs00.html}}</ref> As sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain. By 13,000 years ago, sea level had risen to {{convert|60|m|ft|abbr=on}} lower than at present, and many hills of the coastal plains had become ]. As sea level rise continued, water topped most of the continental islands. The corals could then overgrow the hills, forming ]s and reefs. Sea level on the Great Barrier Reef has not changed significantly in the last 6,000 years.<ref name="AIMSage"/> The age of living reef structure is estimated to be between 6,000 and 8,000 years.<ref name="CRCage">{{cite web|author=CRC Reef Research Centre Ltd |title=What is the Great Barrier Reef? |url=http://www.reef.crc.org.au/discover/coralreefs/coralgbr.html|access-date=May 28, 2006|archive-url= https://web.archive.org/web/20060822015653/http://www.reef.crc.org.au/discover/coralreefs/coralgbr.html |archive-date=August 22, 2006 |url-status=dead}}</ref> Although the Great Barrier Reef formed along a continental shelf, and not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, since Australia is not about to submerge. It formed the world's largest barrier reef, {{convert|300|–|1,000|m|ft|abbr=on}} from shore, stretching for {{convert|2,000|km|mi|abbr=on}}.<ref> {{Webarchive|url=https://web.archive.org/web/20121024014723/http://www.stanford.edu/group/microdocs/typesofreefs.html |date=24 October 2012 }} Microdocs, Stanford Education. Retrieved January 10, 2010.</ref> | ||
Healthy tropical coral reefs grow horizontally from 1 |
Healthy tropical coral reefs grow horizontally from {{convert|1|to|3|cm|in|abbr=on}} per year, and grow vertically anywhere from {{convert|1|to|25|cm|in|abbr=on}} per year; however, they grow only at depths shallower than {{convert|150|m|ft|abbr=on}} because of their need for sunlight, and cannot grow above sea level.<ref>{{cite encyclopedia|author=MSN Encarta |year=2006 |title=Great Barrier Reef |url=http://encarta.msn.com/encyclopedia_761575831/Great_Barrier_Reef.html|access-date=December 11, 2006 |archive-url=https://web.archive.org/web/20091028020755/http://encarta.msn.com/encyclopedia_761575831/Great_Barrier_Reef.html |archive-date=October 28, 2009 |url-status=dead}}</ref> | ||
===Material=== | |||
As the name implies, coral reefs are made up of coral skeletons from mostly intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, ] is formed. However, shell fragments and the remains of ] such as the green-segmented ] '']'' can add to the reef's ability to withstand damage from storms and other threats. Such mixtures are visible in structures such as ].<ref name=murph>{{cite book |title=Coral Reefs: Cities Under The Seas |last=Murphy |first=Richard C. |year=2002 |isbn=978-0-87850-138-0 |publisher=The Darwin Press |url={{google books |plainurl=y |id=WyYVAQAAIAAJ}}}}</ref>{{page needed|date=November 2022}} | |||
=== In the geologic past === | |||
] | |||
The times of maximum reef development were in the ] (513–501 ]), ] (416–359 Ma) and ] (359–299 Ma), owing to ] order ] corals, and ] (100–66 Ma) and ] (23 Ma–present), owing to ] ] corals.<ref>{{Citation |last=Hallock |first=Pamela |title=Reefs and Reef Limestones in Earth History |date=1997 |work=Life and Death of Coral Reefs |pages=13–42 |place=Boston, MA |publisher=Springer US |doi=10.1007/978-1-4615-5995-5_2 |doi-broken-date=2 November 2024 |isbn=978-0-412-03541-8}}</ref> | |||
Not all reefs in the past were formed by corals: those in the ] (542–513 Ma) resulted from calcareous ] and ] (small animals with conical shape, probably related to ]) and in the ] (100–66 Ma), when reefs formed by a group of bivalves called ] existed; one of the valves formed the main conical structure and the other, much smaller valve acted as a cap.<ref name="Johnson_2002" /> | |||
Measurements of the oxygen isotopic composition of the aragonitic skeleton of coral reefs, such as '']'', can indicate changes in ] and sea surface salinity conditions during the growth of the coral. This technique is often used by climate scientists to infer a region's ].<ref name="Cobb">{{cite journal |last1=Cobb |first1=K. |last2=Charles |first2=Christopher D. |last3=Cheng |first3=Hai |last4=Edwards |first4=R. Lawrence |year=2003 |title=El Nino/Southern Oscillation and tropical Pacific climate during the past millennium |url=http://eas8001.eas.gatech.edu/papers/Cobb_Nature_2003.pdf |url-status=dead |journal=Nature |volume=424 |issue=6946 |pages=271–276 |bibcode=2003Natur.424..271C |doi=10.1038/nature01779 |pmid=12867972 |archive-url=https://web.archive.org/web/20120111134948/http://eas8001.eas.gatech.edu/papers/Cobb_Nature_2003.pdf |archive-date=January 11, 2012 |s2cid=6088699}}</ref> | |||
==Types== | ==Types== | ||
Since Darwin's identification of the three classical reef formations – the fringing reef around a volcanic island becoming a barrier reef and then an atoll<ref>Hopley, David (ed.) ''Encyclopedia of Modern Coral Reefs'' Dordrecht: Springer, 2011. p. 40.</ref> – scientists have identified further reef types. While some sources find only three,<ref>e.g. in the Coral Reef Ecology Curriculum. Retrieved 1 Feb 2018.</ref><ref>Whittow, John (1984). ''Dictionary of Physical Geography''. London: Penguin, 1984, p. 443. {{ISBN|0-14-051094-X}}.</ref> Thomas lists "Four major forms of large-scale coral reefs" – the fringing reef, barrier reef, atoll and table reef based on Stoddart, D.R. (1969).<ref name="Thomas">{{cite book |editor-last1=Thomas |editor-first1=David S. G. |title=The Dictionary of Physical Geography |date=2016 |publisher=John Wiley & Sons Inc. |location=Hoboken, NJ |isbn=9781118782347 |page=437 |edition=4th |url=https://geografiafisica.org/sem201901/geo112/bibliografia/articulos_libros/diccionario_de_geografia_fisica_Thomas_John_Wiley_Sons_2016_LIBRO_BUENO.pdf}}</ref><ref name="Stoddart">{{cite journal |last1=Stoddart |first1=D. R. |title=Ecology and morphology of recent coral reefs |journal=Biological Reviews |date=November 1969 |volume=44 |issue=4 |pages=433–498 |doi=10.1111/j.1469-185X.1969.tb00609.x |s2cid=85873056 }}</ref> Spalding ''et al.'' list four main reef types that can be clearly illustrated – the fringing reef, barrier reef, atoll, and "bank or platform reef"—and notes that many other structures exist which do not conform easily to strict definitions, including the "patch reef".<ref>{{cite book |last1=Spalding |first1=Mark |first2=Corinna |last2=Ravilious |first3= Edmund P. |last3=Green |title=World atlas of coral reefs |date=2001 |publisher=University of California Press |location=Berkeley |isbn=0-520-23255-0 |pages=16–}}</ref> | |||
The three principal reef types are: | |||
===Fringing reef=== | |||
* ''']''' – this type is directly attached to a shore, or borders it with an intervening shallow channel or lagoon. | |||
] at the southern tip of ]]] | |||
* '''Barrier reef''' – a reef separated from a mainland or island shore by a deep channel or ] | |||
{{main|Fringing reef}} | |||
* ''']''' – this more or less circular or continuous barrier reef extends all the way around a lagoon without a central island. | |||
] | |||
A fringing reef, also called a shore reef,<ref name=CRISG/> is directly attached to a shore,<ref> at www.pmfias.com. Retrieved 2 Feb 2018.</ref> or borders it with an intervening narrow, shallow channel or lagoon.<ref name=CRA/> It is the most common reef type.<ref name=CRA> at coral.org. Retrieved 2 Feb 2018.</ref> Fringing reefs follow coastlines and can extend for many kilometres.<ref>McClanahan, C.R.C. Sheppard and D.O. Obura. ''Coral Reefs of the Indian Ocean: Their Ecology and Conservation''. Oxford: OUP, 2000, p. 136.</ref> They are usually less than 100 metres wide, but some are hundreds of metres wide.<ref>Goudie, Andrew. ''Encyclopedia of Geomorphology'', London: Routledge, 2004, p. 411.</ref> Fringing reefs are initially formed on the shore at the ] level and expand seawards as they grow in size. The final width depends on where the sea bed begins to drop steeply. The surface of the fringe reef generally remains at the same height: just below the waterline. In older fringing reefs, whose outer regions pushed far out into the sea, the inner part is deepened by erosion and eventually forms a ].<ref>Ghiselin, Michael T. ''The Triumph of the Darwinian Method''. Berkeley, University of California, 1969, p. 22.</ref> Fringing reef lagoons can become over 100 metres wide and several metres deep. Like the fringing reef itself, they run parallel to the coast. The fringing reefs of the ] are "some of the best developed in the world" and occur along all its shores except off sandy bays.<ref>Hanauer, Eric. ''The Egyptian Red Sea: A Diver's Guide''. San Diego: Watersport, 1988, p. 74.</ref> | |||
===Barrier reef=== | |||
] in the ]]] | |||
] in the |
] | ||
Barrier reefs are separated from a mainland or island shore by a deep channel or ].<ref name=CRA/> They resemble the later stages of a fringing reef with its lagoon but differ from the latter mainly in size and origin. Their lagoons can be several kilometres wide and 30 to 70 metres deep. Above all, the offshore outer reef edge formed in open water rather than next to a shoreline. Like an atoll, it is thought that these reefs are formed either as the seabed lowered or sea level rose. Formation takes considerably longer than for a fringing reef, thus barrier reefs are much rarer. | |||
The best known and largest example of a barrier reef is the Australian ].<ref name=CRA/><ref name=CRI> {{Webarchive|url=https://web.archive.org/web/20170913053440/http://www.coral-reef-info.com/types-of-coral-reefs.html |date=September 13, 2017 }} at www.coral-reef-info.com. Retrieved 2 Feb 2018.</ref> Other major examples are the ] and the ].<ref name=CRI/> Barrier reefs are also found on the coasts of ],<ref name=CRI/> ], the ], on the southeast coast of ], on parts of the coast of ], southeastern ] and the south coast of the ]. | |||
Other reef types or variants are: | |||
* '''Patch reef''' – this type is an isolated, comparatively small reef outcrop, usually within a ] or ], often circular and surrounded by sand or seagrass. Patch reefs are common. | |||
* '''Apron reef''' – a short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore | |||
* '''Bank reef''' – a linear or semicircular shaped-outline, larger than a patch reef | |||
* '''Ribbon reef''' – a long, narrow, possibly winding reef, usually associated with an atoll lagoon | |||
* '''Table reef''' – an isolated reef, approaching an atoll type, but without a lagoon | |||
* '''Habili''' – this is a reef in the ] that does not reach the surface near enough to cause visible ], although it may be a hazard to ships (from the ] for "unborn"). | |||
* ''']''' – certain species of corals form communities called microatolls. The vertical growth of microatolls is limited by average tidal height. By analyzing growth morphologies, microatolls offer a low-resolution record of patterns of sea level change. Fossilized microatolls can also be dated using ]. Such methods have been used to reconstruct ] ]s.<ref name=Smithers> | |||
{{cite journal | |||
| author = Smithers, S.G. and Woodroffe, C.D. | |||
| year = 2000 | |||
| title = Microatolls as sea-level indicators on a mid-ocean atoll | |||
| journal = Marine Geology | |||
| volume = 168 | |||
| issue = 1–4 | |||
| pages = 61–78 | |||
| doi = 10.1016/S0025-3227(00)00043-8 | |||
}}</ref> | |||
===Platform reef=== | |||
* ''']s''' – are small, low-elevation, sandy islands formed on the surface of coral reefs. Material eroded from the reef piles up on parts of the reef or lagoon, forming an area above sea level. Plants can stabilize cays enough to become habitable by humans. Cays occur in tropical environments throughout the ], ] and ]s (including the Caribbean and on the ] and ]), where they provide habitable and agricultural land for hundreds of thousands of people. | |||
] | |||
Platform reefs, variously called bank or table reefs, can form on the ], as well as in the open ocean, in fact anywhere where the seabed rises close enough to the surface of the ocean to enable the growth of zooxanthemic, reef-forming corals.<ref name=Leser>{{cite encyclopedia |editor=Leser, Hartmut |year=2005 |title=Wörterbuch Allgemeine Geographie |language=de |edition=13th dtv |location=Munich, DE |page=685 |isbn=978-3-423-03422-7}}</ref> Platform reefs are found in the southern Great Barrier Reef, the Swain<ref>{{cite journal |vauthors=Scoffin TP, Dixon JE |title=The distribution and structure of coral reefs: one hundred years since Darwin |journal=Biological Journal of the Linnean Society |year=1983 |volume=20 |pages=11–38|doi=10.1111/j.1095-8312.1983.tb01587.x }}</ref> and Capricorn Group<ref>{{Cite journal|url=https://espace.library.uq.edu.au/view/UQ:10881 |access-date=2018-06-28 |vauthors=Jell JS, Flood PG |title=Guide to the geology of reefs of the Capricorn and Bunker groups, Great Barrier Reef province |journal=Papers, Department of Geology |volume=8 |issue=3 |at=pp. 1–85, pls. 1–17 |date=Apr 1978}}</ref> on the continental shelf, about 100–200 km from the coast. Some platform reefs of the northern ] are several thousand kilometres from the mainland. Unlike fringing and barrier reefs which extend only seaward, platform reefs grow in all directions.<ref name=Leser/> They are variable in size, ranging from a few hundred metres to many kilometres across. Their usual shape is oval to elongated. Parts of these reefs can reach the surface and form sandbanks and small islands around which may form fringing reefs. A lagoon may form In the middle of a platform reef. | |||
Platform reefs are typically situated within atolls, where they adopt the name "patch reefs" and often span a diameter of just a few dozen meters. In instances where platform reefs develop along elongated structures, such as old and weathered barrier reefs, they tend to arrange themselves in a linear formation. This is the case, for example, on the east coast of the ] near ]. In old platform reefs, the inner part can be so heavily eroded that it forms a pseudo-atoll.<ref name=Leser/> These can be distinguished from real atolls only by detailed investigation, possibly including core drilling. Some platform reefs of the ] are U-shaped, due to wind and water flow. | |||
* When a coral reef cannot keep up with the sinking of a volcanic island, a ''']''' or ''']''' is formed. The tops of seamounts and guyots are below the surface. Seamounts are rounded at the top and guyots are flat. The flat top of the guyot, also called a ''tablemount'', is due to erosion by waves, winds, and atmospheric processes. | |||
== |
===Atoll=== | ||
{{main|Atoll}} | |||
] | |||
]]] | |||
Atolls or ]s are a more or less circular or continuous barrier reef that extends all the way around a lagoon without a central island.<ref>Hopley, David. ''Encyclopedia of Modern Coral Reefs: Structure, Form and Process.'' Dordrecht: Springer, 2011, p. 51.</ref> They are usually formed from fringing reefs around volcanic islands.<ref name=CRA/> Over time, the island ] away and sinks below sea level.<ref name=CRA/> Atolls may also be formed by the sinking of the seabed or rising of the sea level. A ring of reefs results, which enclose a lagoon. Atolls are numerous in the South Pacific, where they usually occur in mid-ocean, for example, in the ], the ], ], the ] and ].<ref name=CRI/> | |||
Atolls are found in the Indian Ocean, for example, in the ], the ], the ] and around ].<ref name=CRI/> The entire Maldives consist of 26 atolls.<ref> at www.mymaldives.com. Retrieved 2 Feb 2018.</ref> | |||
Coral reef ecosystems contain distinct zones that represent different kinds of habitats. Usually, three major zones are recognized: the fore reef, reef crest, and the back reef (frequently referred to as the reef lagoon). | |||
===Other reef types or variants=== | |||
All three zones are physically and ecologically interconnected. Reef life and oceanic processes create opportunities for exchange of ], ]s, nutrients, and marine life among one another. | |||
] in the ]]] | |||
] in the ]]] | |||
* '''Apron reef''' – short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore. The initial stage of a fringing reef.<ref name=CRISG>National Oceanic and Atmospheric Administration. ''Coral Reef Information System Glossary'', 2014.</ref> | |||
Thus, they are integrated components of the coral reef ecosystem, each playing a role in the support of the reefs' abundant and diverse fish assemblages. | |||
* '''Bank reef''' – isolated, flat-topped reef larger than a patch reef and usually on mid-shelf regions and linear or semi-circular in shape; a type of platform reef.<ref name=CRI/> | |||
* '''Patch reef''' – common, isolated, comparatively small reef outcrop, usually within a ] or ], often circular and surrounded by sand or ]. Can be considered as a type of platform reef {{who|date=April 2019}} or as features of fringing reefs, atolls and barrier reefs.<ref name=CRI/> The patches may be surrounded by a ring of reduced seagrass cover referred to as a ''grazing halo''.<ref>{{citation|first1=Hugh|last1=Sweatman|first2=D. Ross|last2=Robertson|date=1994|title=Grazing halos and predation on juvenile Caribbean surgeonfishes|journal=Marine Ecology Progress Series|volume=111|issue=1–6|page=1|doi=10.3354/meps111001|bibcode=1994MEPS..111....1S|url=https://www.int-res.com/articles/meps/111/m111p001.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.int-res.com/articles/meps/111/m111p001.pdf |archive-date=2022-10-09 |url-status=live|access-date=24 April 2019|doi-access=free}}</ref> | |||
* '''Ribbon reef''' – long, narrow, possibly winding reef, usually associated with an atoll lagoon. Also called a shelf-edge reef or sill reef.<ref name=CRISG/> | |||
* '''Drying reef''' – a part of a reef which is above water at low tide but submerged at high tide<ref>{{Cite journal |last=Beazley |first=P. B. |date=1991-01-01 |title=Reefs and the 1982 Convention on the Law of the Sea |url=https://brill.com/view/journals/ijec/6/4/article-p281_1.xml |journal=International Journal of Estuarine and Coastal Law |language=en |volume=6 |issue=4 |pages=281–312 |doi=10.1163/187529991X00162 |issn=0268-0106}}</ref> | |||
* '''Habili''' – reef specific to the ]; does not reach near enough to the surface to cause visible ]; may be a hazard to ships (from the ] for "unborn") | |||
* ''']''' – community of species of corals; vertical growth limited by average tidal height; growth morphologies offer a low-resolution record of patterns of sea level change; fossilized remains can be dated using ] and have been used to reconstruct ] ]s<ref name=Smithers>{{cite journal |author1=Smithers, S.G. |author2=Woodroffe, C.D. |year=2000 |title=Microatolls as sea-level indicators on a mid-ocean atoll |journal=Marine Geology |volume=168 |issue=1–4 |pages=61–78 |doi=10.1016/S0025-3227(00)00043-8| bibcode=2000MGeol.168...61S}}</ref> | |||
* ''']s''' – small, low-elevation, sandy islands formed on the surface of coral reefs from eroded material that piles up, forming an area above sea level; can be stabilized by plants to become habitable; occur in tropical environments throughout the ], ] and ]s (including the Caribbean and on the ] and Belize Barrier Reef), where they provide habitable and agricultural land | |||
* ''']''' or ''']''' – formed when a coral reef on a volcanic island subsides; tops of seamounts are rounded and guyots are flat; flat tops of guyots, or ''tablemounts'', are due to erosion by waves, winds, and atmospheric processes | |||
== Zones == | |||
Most coral reefs exist in shallow waters less than 50 m deep. Some inhabit tropical continental shelves where cool, nutrient rich ] does not occur, such as ]. Others are found in the deep ocean surrounding islands or as ]s, such as in the ]. The reefs surrounding islands form when islands subside into the ocean, and atolls form when an island subsides below the surface of the sea. | |||
] | |||
Coral reef ecosystems contain distinct zones that host different kinds of habitats. Usually, three major zones are recognized: the fore reef, reef crest, and the back reef (frequently referred to as the reef lagoon). | |||
Alternatively, Moyle and Cech distinguish six zones, though most reefs possess only some of the zones.<ref name=MoyleCech556>{{harvnb|Moyle|Cech|2003|p=556}}</ref> | |||
The three zones are physically and ecologically interconnected. Reef life and oceanic processes create opportunities for the exchange of ], ]s, nutrients and marine life. | |||
Most coral reefs exist in waters less than 50 m deep.<ref>{{cite web |url=https://www.marinebio.org/creatures/coral-reefs/ |title=Coral Reefs |website=marinebio.org |date=17 June 2018 |access-date=28 October 2022}}</ref> Some inhabit tropical continental shelves where cool, nutrient-rich ] does not occur, such as the ]. Others are found in the deep ocean surrounding islands or as atolls, such as in the ]. The reefs surrounding islands form when islands subside into the ocean, and atolls form when an island subsides below the surface of the sea. | |||
Alternatively, Moyle and Cech distinguish six zones, though most reefs possess only some of the zones.<ref name=MoyleCech556>{{cite book |last1=Moyle |first1=Peter B. |url={{google books |plainurl=y |id=sZYWAQAAIAAJ}} |title=Fishes : an introduction to ichthyology |year=2004 |publisher=]/] |location=Upper Saddle River, N.J. |isbn=978-0-13-100847-2 |page=556 |edition=Fifth |first2=Joseph J. |last2=Cech}}</ref> | |||
]. The water waves at the left travel over the ''off-reef floor'' until they encounter the ''reef slope'' or ''fore reef''. Then the waves pass over the shallow ''reef crest''. When a wave enters shallow water it ], that is, it slows down and the wave height increases.]] | ]. The water waves at the left travel over the ''off-reef floor'' until they encounter the ''reef slope'' or ''fore reef''. Then the waves pass over the shallow ''reef crest''. When a wave enters shallow water it ], that is, it slows down and the wave height increases.]] | ||
'''The reef surface''' is the shallowest part of the reef. It is subject to ] and ]s. When waves pass over shallow areas, they ], as shown in the adjacent diagram. This means the water is often agitated. These are the precise condition under which corals flourish. The light is sufficient for ] by the symbiotic zooxanthellae, and agitated water brings plankton to feed the coral. | |||
'''The off-reef floor''' is the shallow sea floor surrounding a reef. This zone occurs next to reefs on continental shelves. Reefs around tropical islands and atolls drop abruptly to great depths and do not have such a floor. Usually sandy, the floor often supports ]s which are important foraging areas for reef fish. | |||
'''The reef drop-off''' is, for its first 50 m, habitat for reef fish who find shelter on the cliff face and ] in the water nearby. The drop-off zone applies mainly to the reefs surrounding oceanic islands and atolls. | |||
'''The reef face''' is the zone above the reef floor or the reef drop-off. This zone is often the reef's most diverse area. Coral and ] algae provide complex habitats and areas that offer protection, such as cracks and crevices. Invertebrates and ] algae provide much of the food for other organisms.<ref name=MoyleCech556 /> A common feature on this forereef zone is ]s that serve to transport sediment downslope. | |||
'''The reef flat''' is the sandy-bottomed flat, which can be behind the main reef, containing chunks of coral. This zone may border a lagoon and serve as a protective area, or it may lie between the reef and the shore, and in this case is a flat, rocky area. Fish tend to prefer it when it is present.<ref name=MoyleCech556 /> | |||
'''The reef lagoon''' is an entirely enclosed region, which creates an area less affected by wave action and often contains small reef patches.<ref name=MoyleCech556 /> | |||
However, the |
However, the topography of coral reefs is constantly changing. Each reef is made up of irregular patches of algae, ] invertebrates, and bare rock and sand. The size, shape and relative abundance of these patches change from year to year in response to the various factors that favor one type of patch over another. Growing coral, for example, produces constant change in the fine structure of reefs. On a larger scale, tropical storms may knock out large sections of reef and cause boulders on sandy areas to move.<ref>{{cite journal |journal=] |date=March 24, 1978|volume=199 |issue=4335 |pages=1302–1310 |doi=10.1126/science.199.4335.1302 |title=Diversity in Tropical Rain Forests and Coral Reefs |first=Joseph H. |last=Connell |pmid=17840770 |bibcode=1978Sci...199.1302C}}</ref> | ||
|journal=Science |date=March 24, 1978|volume=199 |issue=4335|pages=1302–1310 | |||
|doi=10.1126/science.199.4335.1302 | |||
|title=Diversity in Tropical Rain Forests and Coral Reefs | |||
|first=Joseph H. |last=Connell | |||
|pmid=17840770}}</ref> | |||
==Locations== | ==Locations== | ||
{{anchor|Darwin Point}} | |||
] | |||
]. Most corals live within this boundary. Note the cooler waters caused by upwelling on the southwest coast of Africa and off the coast of Peru.]] | |||
] | |||
] in red. Coral reefs are not found in coastal areas where colder and nutrient-rich upwellings occur.]] | |||
]. Most corals live within this boundary. Note the cooler waters caused by upwelling on the southwest coast of Africa and off the coast of Peru.]] | |||
] in red. Coral reefs are not found in coastal areas where colder and nutrient-rich upwellings occur.]] | |||
{{See also|List of reefs}} | |||
Coral reefs are estimated to cover 284,300 km<sup>2</sup> (109,800 sq mi),<ref>] (2001) {{Webarchive|url=https://web.archive.org/web/20110707004514/http://coral.unep.ch/atlaspr.htm |date=7 July 2011 }} Coral Reef Unit</ref> just under 0.1% of the oceans' surface area. The ] region (including the ], ], ] and the ]) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including ] accounts for 40.8%. ] and ] coral reefs account for 7.6%.<ref name="Spalding">Spalding, Mark, Corinna Ravilious, and Edmund Green (2001). ''World Atlas of Coral Reefs''. Berkeley, CA: University of California Press and UNEP/WCMC {{ISBN|0520232550}}.</ref> | |||
Although corals exist both in temperate and tropical waters, shallow-water reefs form only in a zone extending from approximately 30° N to 30° S of the equator. Tropical corals do not grow at depths of over {{convert|50|m|sp=us}}. The optimum temperature for most coral reefs is {{convert|26|–|27|C|F}}, and few reefs exist in waters below {{convert|18|C|F}}.<ref>Achituv, Y. and Dubinsky, Z. 1990. Evolution and Zoogeography of Coral Reefs Ecosystems of the World. Vol. 25:1–8.</ref> When the net production by reef building corals no longer keeps pace with relative sea level and the reef structure permanently drowns a '''Darwin Point''' is reached. One such point exists at the northwestern end of the Hawaiian Archipelago; see ].<ref>Grigg, R.W. (2011). Darwin Point. In: Hopley, D. (eds) Encyclopedia of Modern Coral Reefs. Encyclopedia of Earth Sciences Series. Springer, Dordrecht. https://doi.org/10.1007/978-90-481-2639-2_66</ref><ref>G. Flood, | |||
Coral reefs are estimated to cover 284,300 km<sup>2</sup> (109,800 sq mi),<ref>] (2001) Coral Reef Unit</ref> just under 0.1% of the oceans' surface area. The ] region (including the ], ], ] and the ]) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including ] accounts for 40.8%. ] and ] coral reefs account for 7.6%.<ref name="Spalding">Spalding, Mark, Corinna Ravilious, and Edmund Green. 2001. ''World Atlas of Coral Reefs''. Berkeley, CA: University of California Press and UNEP/WCMC.</ref> | |||
The ‘Darwin Point’ of Pacific Ocean atolls and guyots: a reappraisal, Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 175, Issues 1–4, 2001, Pages 147–152, ISSN 0031-0182, https://doi.org/10.1016/S0031-0182(01)00390-X.</ref> | |||
However, reefs in the ] have adapted to temperatures of {{convert|13|C|F}} in winter and {{convert|38|C|F}} in summer.<ref name="Greenpeace"/> 37 species of scleractinian corals inhabit such an environment around ].<ref>{{cite journal|last=Vajed Samiei|first=J.|author2=Dab K.|author3=Ghezellou P. |author4= Shirvani A. |title=Some Scleractinian Corals (Class: Anthozoa) of Larak Island, Persian Gulf|journal=Zootaxa|date=2013|volume=3636|issue=1|pages=101–143|doi=10.11646/zootaxa.3636.1.5|pmid=26042286}}</ref> | |||
Although corals exist both in temperate and tropical waters, shallow-water reefs form only in a zone extending from 30° N to 30° S of the equator. Tropical corals do not grow at depths of over {{convert|50|m|sp=us}}. The optimum temperature for most coral reefs is {{convert|26|–|27|C|F}}, and few reefs exist in waters below {{convert|18|C|F}}.<ref>Achituv, Y. and Dubinsky, Z. 1990. Evolution and Zoogeography of Coral Reefs Ecosystems of the World. Vol. 25:1–8.</ref> However, reefs in the Persian Gulf have adapted to temperatures of {{convert|13|C|F}} in winter and {{convert|38|C|F}} in summer.<ref name="Greenpeace"/> | |||
] |
] inhabits greater depths and colder temperatures at much higher latitudes, as far north as Norway.<ref>{{cite book | ||
|first=Johan Ernst |last=Gunnerus | |first=Johan Ernst |last=Gunnerus | ||
| |
|author-link= Johan Ernst Gunnerus | ||
|title= Om Nogle Norske Coraller | |title= Om Nogle Norske Coraller | ||
|year=1768 | |year=1768 | ||
}}</ref> Although deep water corals can form reefs, |
}}</ref> Although deep water corals can form reefs, little is known about them. | ||
Coral reefs are rare along the ] and ] |
The ] on Earth is located near ], ].<ref>{{Cite web |date=2018-08-05 |title=Coral reef in Eilat, the northernmost reef in the world, is growing |url=https://www.jpost.com/health-science/coral-reef-in-eilat-the-northernmost-reef-in-the-world-is-growing-564175 |access-date=2024-03-04 |website=The Jerusalem Post {{!}} JPost.com |language=en}}</ref> Coral reefs are rare along the west coasts of the ] and ], due primarily to ] and strong cold coastal currents that reduce water temperatures in these areas (the ], ], and ]s, respectively).<ref name="Nybakken">Nybakken, James. 1997. ''Marine Biology: An Ecological Approach.'' 4th ed. Menlo Park, CA: Addison Wesley.</ref> Corals are seldom found along the coastline of ]—from the eastern tip of India (]) to the ] and ] borders<ref name="Spalding" />—as well as along the coasts of northeastern ] and Bangladesh, due to the freshwater release from the ] and ] Rivers respectively. | ||
Significant coral reefs include: | |||
* The ]—largest, comprising over 2,900 individual reefs and 900 islands stretching for over {{convert|2600|km|mi|sp=us}} off ] | * The ]—largest, comprising over 2,900 individual reefs and 900 islands stretching for over {{convert|2600|km|mi|sp=us}} off ] | ||
* The ]—second largest, stretching {{convert|1000|km|mi|sp=us}} from ] at the tip of the ] down to the ] | * The ]—second largest, stretching {{convert|1000|km|mi|sp=us}} from ] at the tip of the ] down to the ] | ||
* The ]—second longest double barrier reef, covering {{convert|1500|km|sp=us}} | * The ]—second longest double barrier reef, covering {{convert|1500|km|sp=us}} | ||
* The ] Barrier Reef—third largest, following the east coast of Andros Island, Bahamas, between ] and ] | * The ] Barrier Reef—third largest, following the east coast of Andros Island, Bahamas, between ] and ] | ||
* The ]—includes |
* The ]—includes 6,000-year-old fringing reefs located along a {{convert|2000|km|mi|-1|abbr=on}} coastline | ||
* The ]—largest continental US reef and the third-largest coral barrier reef, extends from ], located in ], to the ] in the Gulf of Mexico<ref>. Coris.noaa.gov (August 16, 2012). Retrieved on March 3, 2013.</ref> | |||
* ] has the world's largest known ], comprising a 6.4 million acre reef that stretches from Miami to Charleston, S. C. Its discovery was announced in January 2024.<ref name="Sowers">{{cite journal |url= |title=Mapping and Geomorphic Characterization of the Vast Cold-Water Coral Mounds of the Blake Plateau |journal=Geomatics |doi=10.3390/geomatics4010002 |doi-access=free |date=January 12, 2024 |volume=4 |number=1 |pages=17–47 |last1=Sowers |first1=Derek C. |first2=Larry A. |last2=Mayer |first3=Giuseppe |last3=Masetti |first4=Erik |last4=Cordes |first5=Ryan |last5=Gasbarro |first6=Elizabeth |last6=Lobecker |first7=Kasey |last7=Cantwell |first8=Samuel |last8=Candio |first9=Shannon |last9=Hoy |first10=Mashkoor |last10=Malik |display-authors=etal}}</ref> | |||
* ]—deepest photosynthetic coral reef, ] | * ]—deepest photosynthetic coral reef, ] | ||
* Numerous reefs |
* Numerous reefs around the ] | ||
* The ] coral reef area, the second-largest in Southeast Asia, is estimated at 26,000 square kilometres. 915 reef fish species and more than 400 scleractinian coral species, 12 of which are endemic are found there. | |||
* The ] in ]'s ] province offer the highest known marine diversity.<ref>, Ultra Marine: In far eastern Indonesia, the Raja Ampat islands embrace a phenomenal coral wilderness, by David Doubilet, National Geographic, September 2007</ref> | |||
* The ] in ]'s ] province offer the highest known marine diversity.<ref>, Ultra Marine: In far eastern Indonesia, the Raja Ampat islands embrace a phenomenal coral wilderness, by David Doubilet, National Geographic, September 2007</ref> | |||
* ] is known for its northernmost coral reef system, located at {{Coord|32.4|N|64.8|W}}. The presence of coral reefs at this high latitude is due to the proximity of the ]. Bermuda coral species represent a subset of those found in the greater Caribbean.<ref>. Retrieved on May 28, 2015.</ref> | |||
* The world's northernmost ] is located in the Finlayson Channel, in the inside passage of British Columbia, Canada.<ref>{{cite web| url = https://bc.ctvnews.ca/coral-reef-that-shouldn-t-exist-thrives-off-b-c-s-pacific-ocean-biologist-says-1.6804096#:~:text=%E2%80%9CLophelia%20reef%20is%20very%20important,other%20creatures%2C%20Du%20Preez%20said.| title = Coral reef that 'shouldn't exist' thrives off B.C.'s coast in Pacific Ocean, biologist says| last = Shen| first = Nono| date = 12 March 2024| website = CTV News| publisher = The Canadian Press| access-date = 13 March 2024| quote =}}</ref> | |||
* The world's southernmost coral reef is at ], in the Pacific Ocean off the east coast of Australia. | |||
== |
==Coral== | ||
] | ] ] anatomy]] | ||
{{ |
{{main|Coral}} | ||
When alive, corals are ] of small animals embedded in ] shells. Coral heads consist of accumulations of individual animals called ]s, arranged in diverse shapes.<ref>{{cite thesis |degree=Ph.D. |author=Sherman, C.D.H. |year=2006 |url=http://www.library.uow.edu.au/adt-NWU/uploads/approved/adt-NWU20060726.114643/public/02Whole.pdf |title=The Importance of Fine-scale Environmental Heterogeneity in Determining Levels of Genotypic Diversity and Local Adaption |publisher=University of Wollongong |access-date=7 June 2009 |archive-url=https://web.archive.org/web/20080724113051/http://www.library.uow.edu.au/adt-NWU/uploads/approved/adt-NWU20060726.114643/public/02Whole.pdf |archive-date=24 July 2008}}</ref> Polyps are usually tiny, but they can range in size from a pinhead to {{convert|12|in|cm|sp=us}} across. | |||
Reef-building or ]s live only in the ] (above |
Reef-building or ]s live only in the ] (above 70 m), the depth to which sufficient sunlight penetrates the water.<ref>{{Cite web |publisher=National Oceanic and Atmospheric Administration |work=Coral Reef Information System (CoRIS) |title=What are Coral Reefs |url=https://www.coris.noaa.gov/about/what_are/ |access-date=2022-11-09}}</ref> | ||
| coauthors =Marshall, Paul; Schuttenberg, Heidi. | |||
| title =A Reef Manager’s Guide to Coral Bleaching | |||
| publisher = ], | |||
| year = 2006 | |||
| location =Townsville, Australia | |||
| pages = | |||
| url =http://www.gbrmpa.gov.au/corp_site/info_services/publications/misc_pub/a_reef_managers_guide_to_coral_bleaching | |||
| doi = | |||
| isbn = 1-876945-40-0 | |||
| author =Paul Marshall and Heidi Schuttenberg. }}</ref> | |||
===Zooxanthellae=== | |||
Reefs grow as polyps and other organisms deposit calcium carbonate,<ref>Stacy, J., Marion, G., McCulloch, M. and Hoegh-Guldberg, O. "." ''University of Queensland – Centre for Marine Studies.'' May 2007. Accessed 2009-06-07.</ref><ref>Nothdurft, L.D. "." ''Queensland University of Technology Ph.D. Thesis.'' 2007. Accessed 2009-06-07.</ref> the basis of coral, as a skeletal structure beneath and around themselves, pushing the coral head's top upwards and outwards.<ref>Wilson, R.A. "."''Stanford Encyclopedia of Philosophy.'' August 9, 2007. Accessed 2009-06-07.</ref> Waves, grazing fish (such as ]), ]s, ], and other forces and organisms act as ], breaking down coral skeletons into fragments that settle into spaces in the reef structure or form sandy bottoms in associated reef lagoons. Many other organisms living in the reef community contribute skeletal calcium carbonate in the same manner.<ref>Jennings S, Kaiser MJ and Reynolds JD (2001) Wiley-Blackwell, pp. 291–293. ISBN 978-0-632-05098-7.</ref> ] are important contributors to reef structure in those parts of the reef subjected to the greatest forces by waves (such as the reef front facing the open ocean). These algae strengthen the reef structure by depositing limestone in sheets over the reef surface. | |||
], the microscopic algae that lives inside coral, gives it colour and provides it with food through photosynthesis]] | |||
Coral polyps do not photosynthesize, but have a symbiotic relationship with microscopic ] (]s) of the genus '']'', commonly referred to as ]. These organisms live within the polyps' tissues and provide organic nutrients that nourish the polyp in the form of ], ] and ].<ref> {{Webarchive|url=https://web.archive.org/web/20200528115104/https://oceanservice.noaa.gov/education/kits/corals/coral02_zooxanthellae.html |date=28 May 2020 }}. Oceanservice.noaa.gov (March 25, 2008). Retrieved on November 1, 2011.</ref> Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Without their symbionts, coral growth would be too slow to form significant reef structures. Corals get up to 90% of their nutrients from their symbionts.<ref name="GuideCoralBleaching" /> In return, as an example of ], the corals shelter the zooxanthellae, averaging one million for every cubic centimetre of coral, and provide a constant supply of the ] they need for photosynthesis. | |||
] | |||
The colonies of the one thousand coral ] assume a characteristic shape such as ], cabbages, ], ], wire strands and ].{{citation needed|date=December 2010}} | |||
The varying pigments in different species of zooxanthellae give them an overall brown or golden-brown appearance and give brown corals their colors. Other pigments such as reds, blues, greens, etc. come from colored proteins made by the coral animals. Coral that loses a large fraction of its zooxanthellae becomes white (or sometimes pastel shades in corals that are pigmented with their own proteins) and is said to be ], a condition which, unless corrected, can kill the coral. | |||
]]] | |||
] | |||
There are eight ]s of ''Symbiodinium'' ]s. Most research has been conducted on clades A–D. Each clade contributes their own benefits as well as less compatible attributes to the survival of their coral hosts. Each photosynthetic organism has a specific level of sensitivity to photodamage to compounds needed for survival, such as proteins. Rates of regeneration and replication determine the organism's ability to survive. Phylotype A is found more in the shallow waters. It is able to produce ]s that are ], using a derivative of ] to absorb the UV radiation and allowing them to better adapt to warmer water temperatures. In the event of UV or thermal damage, if and when repair occurs, it will increase the likelihood of survival of the host and symbiont. This leads to the idea that, evolutionarily, clade A is more UV resistant and thermally resistant than the other clades.<ref name="Reynolds">{{cite journal|vauthors=Reynolds J, Bruns B, Fitt W, Schmidt G|year=2008|title=Enhanced photoprotection pathways in symbiotic dinoflagellates of shallow-water corals and other cnidarians|journal=Proceedings of the National Academy of Sciences|volume=105|issue=36|pages=13674–13678|bibcode=2008PNAS..10513674R|doi=10.1073/pnas.0805187105|pmid=18757737|pmc=2527352|doi-access=free}}</ref> | |||
Corals reproduce both sexually and asexually. An individual polyp uses both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. The reproductive cells are found on the ] membranes that radiate inward from the layer of tissue that lines the stomach cavity. Some mature adult corals are hermaphroditic; others are exclusively male or female. A few ] change sex as they grow. | |||
Clades B and C are found more frequently in deeper water, which may explain their higher vulnerability to increased temperatures. Terrestrial plants that receive less sunlight because they are found in the undergrowth are analogous to clades B, C, and D. Since clades B through D are found at deeper depths, they require an elevated light absorption rate to be able to synthesize as much energy. With elevated absorption rates at UV wavelengths, these phylotypes are more prone to coral bleaching versus the shallow clade A. | |||
Internally fertilized eggs develop in the polyp for a period ranging from days to weeks. Subsequent development produces a tiny ], known as a ]. Externally fertilized eggs develop during synchronized spawning. Polyps release eggs and sperm into the water en masse, simultaneously. Eggs disperse over a large area. The timing of spawning depends on time of year, water temperature, and tidal and lunar cycles. Spawning is most successful when there is little variation between high and low ]. The less water movement, the better the chance for fertilization. Ideal timing occurs in the spring. Release of eggs or planula usually occurs at night, and is sometimes in phase with the lunar cycle (three to six days after a full moon). The period from release to settlement lasts only a few days, but some planulae can survive afloat for several weeks. They are vulnerable to predation and environmental conditions. The lucky few planulae which successfully attach to substrate next confront competition for food and space.{{citation needed|date=December 2010}} | |||
Clade D has been observed to be high temperature-tolerant, and has a higher rate of survival than clades B and C during modern ].<ref name="Reynolds" /> | |||
<gallery> | |||
File:Brain coral.jpg|] | |||
===Skeleton=== | |||
File:Staghorn-coral-1.jpg|] | |||
] sp.'']] | |||
Reefs grow as polyps and other organisms deposit calcium carbonate,<ref>{{cite web |vauthors=Stacy J, Marion G, McCulloch M, Hoegh-Guldberg O |title=Long-term changes to Mackay Whitsunday water quality and connectivity between terrestrial, mangrove and coral reef ecosystems: Clues from coral proxies and remote sensing records |series=Synthesis of research from an ARC Linkage Grant (2004–2007) |url-status=dead |publisher=University of Queensland |department=Centre for Marine Studies |date=May 2007 |url=http://www.marine.uq.edu.au/mackayarc/Reports%20&%20publications/Mackay_ARC_2007_lowres.pdf |access-date=7 June 2009 |archive-date=August 30, 2007 |archive-url=https://web.archive.org/web/20070830013615/http://marine.uq.edu.au/mackayarc/Reports%20%26%20publications/Mackay_ARC_2007_lowres.pdf}}</ref><ref>{{cite thesis |last=Nothdurft |first=Luke D. |url=https://eprints.qut.edu.au/16690/1/Luke_D._Nothdurft_Thesis.pdf |archive-url=https://web.archive.org/web/20110309095832/https://eprints.qut.edu.au/16690/1/Luke_D._Nothdurft_Thesis.pdf |archive-date=2011-03-09 |url-status=live |title=Microstructure and early diagenesis of recent reef building scleractinian corals, Heron reef, Great Barrier Reef: implications for paleoclimate analysis |publisher=Queensland University of Technology |degree=Ph.D. |date=2007 |publication-date=2008 |access-date=2022-11-10 |via=}} {{Webarchive|url=https://web.archive.org/web/20221111063847/https://eprints.qut.edu.au/16690/ |date=11 November 2022 }}</ref> the basis of coral, as a skeletal structure beneath and around themselves, pushing the coral head's top upwards and outwards.<ref>{{cite encyclopedia |vauthors=Wilson RA |url=http://plato.stanford.edu/entries/biology-individual/ |article=The Biological Notion of Individual |title=Stanford Encyclopedia of Philosophy |date=9 August 2007 |access-date=7 June 2009}}</ref> Waves, grazing fish (such as ]), ]s, ] and other forces and organisms act as ], breaking down coral skeletons into fragments that settle into spaces in the reef structure or form sandy bottoms in associated reef lagoons. | |||
Typical shapes for coral ] are named by their resemblance to terrestrial objects such as ], cabbages, ], ], wire strands and ]. These shapes can depend on the life history of the coral, like light exposure and wave action,<ref>{{cite journal |last=Chappell |first=John |title=Coral morphology, diversity and reef growth |journal=Nature |date=17 July 1980 |volume=286 |issue=5770 |pages=249–252 |doi=10.1038/286249a0 |bibcode=1980Natur.286..249C |s2cid=4347930 }}</ref> and events such as breakages.<ref>{{cite journal |last=Jackson |first=Jeremy B. C. |title=Adaptation and Diversity of Reef Corals |journal=BioScience |date=1 July 1991 |volume=41 |issue=7 |pages=475–482 |doi=10.2307/1311805 |jstor=1311805}}</ref> | |||
{{clear left}} | |||
===Reproduction=== | |||
] and attached to the ocean floor. But unlike plants, corals do not make their own food.<ref> ''NOAA: National Ocean Service''. Accessed 11 February 2020. Updated: 7 January 2020.</ref>]] | |||
{{external media | width = 210px | float = right | headerimage= ] | video1 = , Tom Shlesinger, Sep 5, 2019.}} | |||
Corals reproduce both sexually and asexually. An individual polyp uses both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. The reproductive cells are found on the ], membranes that radiate inward from the layer of tissue that lines the stomach cavity. Some mature adult corals are hermaphroditic; others are exclusively male or female. A few ] change sex as they grow. | |||
Internally fertilized eggs develop in the polyp for a period ranging from days to weeks. Subsequent development produces a tiny ], known as a ]. Externally fertilized eggs develop during synchronized spawning. Polyps across a reef simultaneously release eggs and sperm into the water en masse. Spawn disperse over a large area. The timing of spawning depends on time of year, water temperature, and tidal and lunar cycles. Spawning is most successful given little variation between high and low ]. The less water movement, the better the chance for fertilization. The release of eggs or planula usually occurs at night and is sometimes in phase with the lunar cycle (three to six days after a full moon).<ref name="Markandeya">{{cite journal |last1=Markandeya |first1=Virat |title=How lunar cycles guide the spawning of corals, worms and more |journal=Knowable Magazine |publisher= Annual Reviews |date=22 February 2023 |doi=10.1146/knowable-022223-2 |doi-access=free |url=https://knowablemagazine.org/article/living-world/2023/lunar-cycles-guide-spawning |access-date=6 March 2023 |language=en}}</ref><ref name="Häfker">{{cite journal |last1=Häfker |first1=N. Sören |last2=Andreatta |first2=Gabriele |last3=Manzotti |first3=Alessandro |last4=Falciatore |first4=Angela |last5=Raible |first5=Florian |last6=Tessmar-Raible |first6=Kristin |title=Rhythms and Clocks in Marine Organisms |journal=Annual Review of Marine Science |date=16 January 2023 |volume=15 |issue=1 |pages=509–538 |doi=10.1146/annurev-marine-030422-113038 |pmid=36028229 |bibcode=2023ARMS...15..509H |s2cid=251865474 |language=en |issn=1941-1405|doi-access=free }}</ref><ref name="Lin">{{cite journal |last1=Lin |first1=Che-Hung |last2=Takahashi |first2=Shunichi |last3=Mulla |first3=Aziz J. |last4=Nozawa |first4=Yoko |title=Moonrise timing is key for synchronized spawning in coral Dipsastraea speciosa |journal=Proceedings of the National Academy of Sciences |date=24 August 2021 |volume=118 |issue=34 |pages=e2101985118 |doi=10.1073/pnas.2101985118 |pmid=34373318 |pmc=8403928 |bibcode=2021PNAS..11801985L |language=en |issn=0027-8424 |doi-access=free }}</ref> | |||
] | |||
The period from release to settlement lasts only a few days, but some planulae can survive afloat for several weeks. During this process, the larvae may use several different cues to find a suitable location for settlement. At long distances sounds from existing reefs are likely important,<ref name="Vermeij 2010">{{cite journal |last1=Vermeij |first1=Mark J. A. |last2=Marhaver |first2=Kristen L. |last3=Huijbers |first3=Chantal M. |last4=Nagelkerken |first4=Ivan |last5=Simpson |first5=Stephen D. |title=Coral larvae move toward reef sounds |journal=PLOS ONE |date=2010 |volume=5 |issue=5 |pages=e10660 |doi=10.1371/journal.pone.0010660|pmid=20498831 |doi-access=free |pmc=2871043 |bibcode=2010PLoSO...510660V }}</ref> while at short distances chemical compounds become important.<ref name="Gleason 2009">{{cite journal |last1=Gleason |first1=D. F. |last2=Danilowicz |first2=B. S. |last3=Nolan |first3=C. J. |title=Reef waters stimulate substratum exploration in planulae from brooding Caribbean corals |journal=Coral Reefs |date=2009 |volume=28 |issue=2 |pages=549–554 |doi=10.1007/s00338-009-0480-1|bibcode=2009CorRe..28..549G |s2cid=39726375 }}</ref> The larvae are vulnerable to predation and environmental conditions. The lucky few planulae that successfully attach to substrate then compete for food and space.{{citation needed|date=December 2010}} | |||
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==Gallery of reef-building corals== | |||
{| | |||
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| width=550px | <gallery mode="packed"> | |||
File:Fluorescent coral - MBA - DSC07089.JPG|Fluorescent coral<ref>{{cite web|url=http://photography.nationalgeographic.com/wallpaper/photography/photos/coral-kingdoms/fluorescent-coral-laman/ |archive-url=https://web.archive.org/web/20100629212418/http://photography.nationalgeographic.com/wallpaper/photography/photos/coral-kingdoms/fluorescent-coral-laman |url-status=dead |archive-date=29 June 2010 |title=Fluorescent coral |publisher=National Geographic Society|department=photography|series=Coral kingdoms}}</ref> | |||
File:Cirripathes sp (Spiral Wire Coral).jpg|Spiral wire coral | File:Cirripathes sp (Spiral Wire Coral).jpg|Spiral wire coral | ||
File:Muchroom coral.JPG|] | |||
File:Staghorn-coral-1.jpg|] | |||
File:PillarCoral.jpg|] | File:PillarCoral.jpg|] | ||
File:Brain coral.jpg|] | |||
File:Meandrina meandrites (Maze Coral).jpg|] | |||
File:Black coral.jpg|] | |||
File:Elkhorn Coral with a Yellowtail Damselfish in the Caribbean Sea in Curaçao.jpg|] | |||
</gallery> | </gallery> | ||
| <gallery mode="packed" heights="400"> | |||
File:Fluorescent Coral Movie.gif|{{center|Fluorescent coral}} | |||
</gallery> | |||
|} | |||
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==Other reef builders== | |||
] are the most prodigious reef-builders. However many other organisms living in the reef community contribute skeletal calcium carbonate in the same manner as corals. These include ], ] and ]s.<ref>{{cite book |vauthors=Jennings S, Kaiser MJ, Reynolds JD |year=2001 |url={{google books |plainurl=y |id=oTVyeNQyoiMC}}|title=Marine Fisheries Ecology |pages=291–293 |publisher=Wiley-Blackwell |isbn=978-0-632-05098-7}}</ref> Reefs are always built by the combined efforts of these different ], with different organisms leading reef-building in different ]s.<ref>{{cite journal |last1=Kuznetsov |first1=Vitaly |title=The evolution of reef structures through time: Importance of tectonic and biological controls |journal=Facies |date=1 December 1990 |volume=22 |issue=1 |pages=159–168 |doi=10.1007/BF02536950|bibcode=1990Faci...22..159K |s2cid=127193540 }}</ref> | |||
===Coralline algae=== | |||
{{main|Coralline algae}} | |||
{{See also|Coralline rock}} | |||
] ''] sp.'']] | |||
] are important contributors to reef structure. Although their mineral deposition rates are much slower than corals, they are more tolerant of rough wave-action, and so help to create a protective crust over those parts of the reef subjected to the greatest forces by waves, such as the reef front facing the open ocean. They also strengthen the reef structure by depositing limestone in sheets over the reef surface.{{citation needed |date=June 2018}} | |||
===Sponges=== | |||
{{Unreferenced section|date=December 2024}} | |||
{{main|Sponge reef}} | |||
]]] | |||
"]" is the descriptive name for all ] that build ]. In the early ], ] were the world's first reef-building organisms, and sponges were the only reef-builders until the ]. ]s still assist corals building modern reefs, but like ] are much slower-growing than corals and their contribution is (usually) minor.{{citation needed |date=June 2018}} | |||
In the northern Pacific Ocean ]s still create deep-water mineral-structures without corals, although the structures are not recognizable from the surface like tropical reefs. They are the only ] organisms known to build reef-like structures in cold water.{{citation needed |date=June 2018}} | |||
===Bivalves=== | |||
{{See also|Bivalve reef}} | |||
]s (''Crassostrea virginica'')]] | |||
]s are dense aggregations of ]s living in colonial communities. Other regionally-specific names for these structures include oyster beds and oyster banks. Oyster larvae require a hard substrate or surface to attach on, which includes the shells of old or dead oysters. Thus reefs can build up over time as new larvae settle on older individuals. '']'' were once abundant in ] and shorelines bordering the ] until the late nineteenth century.<ref>Newell, R.I.E. 1988. Ecological changes in Chesapeake Bay: are they the results of ] the American oyster, ''Crassostrea virginica''? In: M. Lynch and E.C. Krome (eds.) Understanding the estuary: advances in Chesapeake Bay research, Chesapeake Research Consortium, Solomons MD pp.536–546.</ref> '']'' is a species of flat oyster that had also formed large reefs in South Australia.<ref name=good>{{cite web |title=4 things you might not know about South Australia's new shellfish reef |website=Government of South Australia. ] |date=10 May 2019 |url=https://www.environment.sa.gov.au/goodliving/posts/2019/05/windara-reef |access-date=28 February 2021}}</ref> | |||
Hippuritida, an extinct order of bivalves known as ], were major reef-building organisms during the ]. By the mid-Cretaceous, rudists became the dominant tropical reef-builders, becoming more numerous than scleractinian corals. During this period, ocean temperatures and saline levels—which corals are sensitive to—were higher than it is today, which may have contributed to the success of rudist reefs.<ref name=Johnson_2002>{{cite journal |author=Johnson, C. |year=2002 |title=The rise and fall of Rudist reefs |journal=American Scientist |volume=90 |issue=2 |page=148 |doi=10.1511/2002.2.148 |bibcode=2002AmSci..90..148J |s2cid=121693025 }}</ref> | |||
===Gastropods=== | |||
Some gastropods, like family ], are sessile and cement themselves to the substrate, contributing to the reef building.<ref>{{cite journal | url=https://www.sciencedirect.com/science/article/abs/pii/S0031018208003672 | doi=10.1016/j.palaeo.2008.06.008 | title=Vermetid reefs and their use as palaeobathymetric markers: New insights from the Late Miocene of the Mediterranean (Southern Italy, Crete) | journal=Palaeogeography, Palaeoclimatology, Palaeoecology | date=19 September 2008 | volume=267 | issue=1 | pages=89–101 | last1=Vescogni | first1=Alessandro | last2=Bosellini | first2=Francesca R. | last3=Reuter | first3=Markus | last4=Brachert | first4=Thomas C. | bibcode=2008PPP...267...89V }}</ref> | |||
{{clear}} | |||
==Darwin's paradox== | ==Darwin's paradox== | ||
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| quote = {{center|'''Darwin's paradox'''}}"Coral... seems to proliferate when ocean waters are warm, poor, clear and agitated, a fact which Darwin had already noted when he passed through Tahiti in 1842. This constitutes a fundamental paradox, shown quantitatively by the apparent impossibility of balancing input and output of the nutritive elements which control the coral polyp metabolism. | ||
This constitutes a fundamental paradox, shown quantitatively by the apparent impossibility of balancing input and output of the nutritive elements which control the coral polyp metabolism. | |||
Recent oceanographic research has brought to light the reality of this paradox by confirming that the ] of the ocean ] zone persists right up to the swell-battered reef crest. When you approach the reef edges and atolls from the quasidesert of the open sea, the near absence of living matter suddenly becomes a plethora of life, without transition. So why is there something rather than nothing, and more precisely, where do the necessary nutrients for the functioning of this extraordinary coral reef machine come from |
Recent oceanographic research has brought to light the reality of this paradox by confirming that the ] of the ocean ] zone persists right up to the swell-battered reef crest. When you approach the reef edges and atolls from the quasidesert of the open sea, the near absence of living matter suddenly becomes a plethora of life, without transition. So why is there something rather than nothing, and more precisely, where do the necessary nutrients for the functioning of this extraordinary coral reef machine come from?" | ||
— Francis Rougerie<ref>Rougerier, F ''ORSTOM'', Papeete.</ref> |
— Francis Rougerie<ref>{{cite book|editor=Jost, Christian |chapter-url={{google books |plainurl=y |id=RTQEAQAAIAAJ}}|title=The French-Speaking Pacific: Population, Environment and Development Issues|year=1998|publisher=Boombana Publications|isbn=978-1-876542-02-3 |author=Rougerier, F |id= (pdf: ) |chapter=The functioning of coral reefs and atolls: from paradox to paradigm}}</ref> | ||
}} | |||
In '']'', published in 1842, Darwin described how coral reefs were found in some tropical areas but not others, with no obvious cause. The largest and strongest corals grew in parts of the reef exposed to the most violent surf and corals were weakened or absent where loose sediment accumulated.<ref name="The structure and distribution of coral reefs"/>{{rp|}} | |||
During his voyage on the ''Beagle'', Darwin described tropical coral reefs as ] in the ] of the ocean. He reflected on the paradox that tropical coral reefs, which are among the richest and most ] ecosystems on earth, flourish surrounded by tropical ocean waters that provide hardly any nutrients.{{Citation needed|date=April 2011}} | |||
Tropical waters contain few nutrients<ref>{{Cite book|chapter-url={{google books |plainurl=y |id=eLoKAQAAIAAJ|page=56}} |title=Perspectives on Coral Reefs |editor-last=Barnes |editor-first=D.J. |date=1983 |publisher=Australian Institute of Marine Science |isbn=9780642895851 |last=Crossland |first=C.J. |chapter=Dissolved nutrients in coral reef waters |pages=56–68}}</ref> yet a coral reef can flourish like an "oasis in the desert".<ref>{{Cite book|url={{google books |plainurl=y |id=r1hfQwAACAAJ}} |title=Fundamentals of Ecology |edition=3rd |date=1971 |publisher=Saunders |last=Odum |first=E.P.}}</ref> This has given rise to the ecosystem conundrum, sometimes called "Darwin's paradox": "How can such high production flourish in such nutrient poor conditions?"<ref>{{cite journal |last1=Sammarco |first1=PW |last2=Risk |first2=MJ |last3=Schwarcz |first3=HP |last4=Heikoop |first4=JM |year=1999 |title=Cross-continental shelf trends in coral δ15N on the Great Barrier Reef: further consideration of the reef nutrient paradox |url=https://www.int-res.com/articles/meps/180/m180p131.pdf |journal=Mar Ecol Prog Ser |volume=180 |pages=131–138 |doi=10.3354/meps180131 |doi-access=free |bibcode=1999MEPS..180..131S}}</ref><ref>{{cite journal |last1=Rougerie |first1=F |last2=Wauthy |first2=B |year=1993 |title=The endo-upwelling concept: from geothermal convection to reef construction |url=http://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_6/b_fdi_33-34/38976.pdf |journal=Coral Reefs |volume=12 |issue=1| pages=19–30 |bibcode=1993CorRe..12...19R |s2cid=27590358 |doi=10.1007/bf00303781}}</ref><ref name=Goeij2009>De Goeij, Jasper M (2009) PhD thesis, page 13. University of Groningen.</ref> | |||
Coral reefs cover less than 0.1% of the surface of the world’s ocean, yet they support over one-quarter of all marine species. This diversity results in complex ]s, with large ] eating smaller ] that eat yet smaller ] and so on. However, all food webs eventually depend on ]s, which are the ]. Coral reefs' ] is very high, typically producing 5–10 g·cm<sup>−2</sup>·day<sup>−1</sup> ].<ref>{{cite book |last=Sorokin |first=Yuri I. |title=Coral Reef Ecology |location=Germany |publisher=Sringer-Herlag, Berlin Heidelberg |year=1993 |isbn=978-0-387-56427-2 }}</ref><!--what does the C in the measurement indicate?--> | |||
Coral reefs support over one-quarter of all marine species. This diversity results in complex ]s, with large ] eating smaller ] that eat yet smaller ] and so on. However, all food webs eventually depend on ]s, which are the ]. Coral reefs typically produce 5–10 grams of carbon per square meter per day (gC·m<sup>−2</sup>·day<sup>−1</sup>) ].<ref>{{cite book |last=Sorokin |first=Yuri I. |url={{google books |plainurl=y |id=6CbePgAACAAJ}} |title= Coral Reef Ecology |location=Germany |publisher= Springer-Verlag, Berlin Heidelberg |year=1993 |isbn=978-0-387-56427-2 }}</ref><ref>{{cite journal|last=Hatcher|first=Bruce Gordon|title=Coral reef primary productivity: A beggar's banquet|journal=Trends in Ecology & Evolution|date=1 May 1988|volume=3|issue=5|pages=106–111|doi=10.1016/0169-5347(88)90117-6|pmid=21227159|bibcode=1988TEcoE...3..106H }}</ref> | |||
One reason for the unusual clarity of tropical waters is they are deficient in nutrients and drifting ]. Further, the sun shines year round in the tropics, warming the surface layer, making it less dense than subsurface layers.<!-- why is this warm sunny water low in nutrients? are reef waters less nourishing than deep ocean waters? --> The warmer water is separated from deeper, cooler water by a stable ], where the temperature makes a rapid change. This keeps the warm surface waters floating above the cooler deeper waters. In most parts of the ocean, there is little exchange between these layers. Organisms that die in aquatic environments generally sink to the bottom, where they decompose, which releases nutrients in the form of ] (N), ] (P) and ] (K). These nutrients are necessary for plant growth, but in the tropics, they do not directly return to the surface.<ref name=Anderson2003>{{cite web |last=Anderson |first=Genny |year=2003 |url=http://www.marinebio.net/marinescience/04benthon/crform. |title=htm Coral Reef Formation |work=Marinebio.net |accessdate=April 5, 2011}}</ref><!-- this is an online college course, but it appears to be the work of one author and includes no citations. i suggest finding an alternative.--> | |||
One reason for the unusual clarity of tropical waters is their nutrient deficiency and drifting ]. Further, the sun shines year-round in the tropics, warming the surface layer, making it less dense than subsurface layers.<!-- why is this warm sunny water low in nutrients? are reef waters less nourishing than deep ocean waters? --> The warmer water is separated from deeper, cooler water by a stable ], where the temperature makes a rapid change. This keeps the warm surface waters floating above the cooler deeper waters. In most parts of the ocean, there is little exchange between these layers. Organisms that die in aquatic environments generally sink to the bottom, where they decompose, which releases nutrients in the form of ] (N), ] (P) and ] (K). These nutrients are necessary for plant growth, but in the tropics, they do not directly return to the surface.{{citation needed|date=September 2013}} | |||
Plants form the base of the food chain, and need sunlight and nutrients to grow. In the ocean, these plants are mainly microscopic ] which drift in the ]. They need sunlight for ], which powers ], so they are found only relatively near the surface. But they also need nutrients. Phytoplankton rapidly use nutrients in the surface waters, and in the tropics, these nutrients are not usually replaced because of the ].<ref name=Anderson2003 /> | |||
Plants form the base of the food chain and need sunlight and nutrients to grow. In the ocean, these plants are mainly microscopic ] which drift in the ]. They need sunlight for ], which powers ], so they are found only relatively near the surface, but they also need nutrients. Phytoplankton rapidly use nutrients in the surface waters, and in the tropics, these nutrients are not usually replaced because of the ].<ref>{{Cite journal|last1=Ross|first1=On|last2=Sharples|first2=J|date=2007-10-11|title=Phytoplankton motility and the competition for nutrients in the thermocline|url=http://www.int-res.com/abstracts/meps/v347/p21-38/|journal=Marine Ecology Progress Series|language=en|volume=347|pages=21–38|doi=10.3354/meps06999|bibcode=2007MEPS..347...21R|issn=0171-8630|doi-access=free}}</ref> | |||
] | |||
===Explanations=== | |||
Around coral reefs, lagoons fill in with material eroded from the reef and the island. They become havens for marine life, providing protection from waves and storms. | Around coral reefs, lagoons fill in with material eroded from the reef and the island. They become havens for marine life, providing protection from waves and storms. | ||
Most importantly, reefs ] nutrients, which happens much less in the open ocean. In coral reefs and lagoons, producers include phytoplankton, as well as seaweed and coralline algae, especially small types called turf algae, which pass nutrients to corals.<ref name="Castro" /> The phytoplankton |
Most importantly, reefs ] nutrients, which happens much less in the open ocean. In coral reefs and lagoons, producers include phytoplankton, as well as seaweed and coralline algae, especially small types called turf algae, which pass nutrients to corals.<ref name="Castro" /> The phytoplankton form the base of the food chain and are eaten by fish and crustaceans. Recycling reduces the nutrient inputs needed overall to support the community.<ref name="GuideCoralBleaching">{{cite book |author1=Marshall, Paul |author2=Schuttenberg, Heidi |year=2006 |title=A Reef Manager's Guide to Coral Bleaching |publisher=Great Barrier Reef Marine Park Authority |location=Townsville, Australia |url=http://www.coris.noaa.gov/activities/reef_managers_guide/ |isbn=978-1-876945-40-4}}</ref> | ||
Corals also absorb nutrients, including inorganic nitrogen and phosphorus, directly from water. Many corals extend their tentacles at night to catch ] that pass near. Zooplankton provide the polyp with nitrogen, and the polyp shares some of the nitrogen with the zooxanthellae, which also require this element.<ref name="Castro">Castro, Peter and Huber, Michael (2000) ''Marine Biology.'' 3rd ed. Boston: McGraw-Hill.</ref> | |||
] and pigmented proteins (reds, blues, greens, etc.) produced by the corals themselves.]] | |||
Sponges live in crevices in the reefs. They are efficient ]s, and in the ] they consume about 60% of the phytoplankton that drifts by. Sponges eventually excrete nutrients in a form that corals can use.<ref>{{cite web |url=http://news.nationalgeographic.com/news/2001/11/1107_keyholecoral.html |archive-url=https://web.archive.org/web/20011108233132/http://news.nationalgeographic.com/news/2001/11/1107_keyholecoral.html |url-status=dead |archive-date=8 November 2001 |title=Rich Coral Reefs in Nutrient-Poor Water: Paradox Explained? |first=John |last=Roach |publisher=] |date=November 7, 2001 |access-date=April 5, 2011}}</ref> | |||
The roughness of coral surfaces is key to coral survival in agitated waters. Normally, a boundary layer of still water surrounds a submerged object, which acts as a barrier. Waves breaking on the extremely rough edges of corals disrupt the boundary layer, allowing the corals access to passing nutrients. Turbulent water thereby promotes reef growth. Without the access to nutrients brought by rough coral surfaces, even the most effective recycling would not suffice.<ref>{{cite journal |url=https://www.newscientist.com/article/mg17523612.100-corals-play-rough-over-darwins-paradox.html |title=Corals play rough over Darwin's paradox |first=Rachel |last=Nowak |issue=2361 |journal=] |date=21 September 2002 }}</ref> | |||
Deep nutrient-rich water entering coral reefs through isolated events may have significant effects on temperature and nutrient systems.<ref name="Leichter et al. 1996">{{cite journal|last=Leichter|first=J. |author2=Wing S. |author3=Miller S.|author4=Denny M.|title=Pulsed delivery of subthermocline water to Conch Reef (Florida Keys) by internal tidal bores|journal=Limnology and Oceanography|year=1996|volume=41 |issue=7|pages=1490–1501 |doi=10.4319/lo.1996.41.7.1490|bibcode=1996LimOc..41.1490L|doi-access=free}}</ref><ref name="Wolanski and Pickard 1983">{{Cite journal |last1=Wolanski |first1=E. |last2=Pickard |first2=G. L. |doi=10.1071/MF9830065 |title=Upwelling by internal tides and kelvin waves at the continental shelf break on the Great Barrier Reef |journal=Marine and Freshwater Research |volume=34 |page=65 |year=1983}}</ref> This water movement disrupts the relatively stable thermocline that usually exists between warm shallow water and deeper colder water. Temperature regimes on coral reefs in the Bahamas and Florida are highly variable with temporal scales of minutes to seasons and spatial scales across depths.<ref>{{cite journal|last=Leichter|first=J.|author2=Helmuth B.|author3=Fischer A.|year=2006 |title=Variation beneath the surface: Quantifying complex thermal environments on coral reefs in the Caribbean, Bahamas and Florida|journal=Journal of Marine Research|volume=64|issue=4|pages=563–588 |doi=10.1357/002224006778715711|doi-broken-date=2 December 2024 }}</ref> | |||
Coral reefs support many ] relationships. In particular, ] provide energy to coral in the form of ], ], and ].<ref>. Oceanservice.noaa.gov (2008-03-25). Retrieved on 2011-11-01.</ref> Zooxanthellae can provide up to 90% of a coral’s energy requirements.<ref name="GuideCoralBleaching">{{cite book | |||
| coauthors =Marshall, Paul; Schuttenberg, Heidi. | |||
| title =A Reef Manager’s Guide to Coral Bleaching | |||
| publisher = ], | |||
| year = 2006 | |||
| location =Townsville, Australia | |||
| url =http://www.gbrmpa.gov.au/corp_site/info_services/publications/misc_pub/a_reef_managers_guide_to_coral_bleaching | |||
| isbn = 1-876945-40-0 }}</ref> In return, as an example of ], the corals shelter the zooxanthellae, averaging one million for every cubic centimeter of coral, and provide a constant supply of the ] they need for photosynthesis. | |||
] | |||
] and pigmented proteins (reds, blues, greens, etc.) produced by the corals themselves.]] | |||
Water can pass through coral reefs in various ways, including current rings, surface waves, internal waves and tidal changes.<ref name="Leichter et al. 1996" /><ref name="Ezer et al. 2011">{{cite journal |last=Ezer|first=T.|author2=Heyman W.|author3=Houser C.|author4=Kjerfve B.|title=Modeling and observations of high-frequency flow variability and internal waves at a Caribbean reef spawning aggregation site|journal=Ocean Dynamics|year=2011|volume=61|issue=5|pages=581–598|doi=10.1007/s10236-010-0367-2|bibcode=2011OcDyn..61..581E|s2cid=55252988}}</ref><ref name="Fratantoni and Richardson 2006">{{cite journal|last=Fratantoni |first=D. |author2=Richardson P.|title=The Evolution and Demise of North Brazil Current Rings|journal=Journal of Physical Oceanography|year=2006|volume=36|issue=7|pages=1241–1249 |doi=10.1175/JPO2907.1 |bibcode=2006JPO....36.1241F |hdl=1912/4221|hdl-access=free |url=http://darchive.mblwhoilibrary.org/bitstream/1912/4221/1/jpo2907%252E1.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://darchive.mblwhoilibrary.org/bitstream/1912/4221/1/jpo2907%252E1.pdf |archive-date=2022-10-09 |url-status=live}}</ref><ref name="Leichter et al. 1998">{{cite journal |last=Leichter|first=J.|author2=Shellenbarger G.|author3=Genovese S.|author4=Wing S.|title=Breaking internal waves on a Florida (USA) coral reef: a plankton pump at work?|journal=Marine Ecology Progress Series|year=1998 |volume=166|pages=83–97|doi=10.3354/meps166083|bibcode=1998MEPS..166...83L|doi-access=free}}</ref> Movement is generally created by tides and wind. As tides interact with varying bathymetry and wind mixes with surface water, internal waves are created. An internal wave is a gravity wave that moves along density stratification within the ocean. When a water parcel encounters a different density it oscillates and creates internal waves.<ref name="Talley et al. 2011">{{cite book|last=Talley|first=L.|url={{google books |plainurl=y |id=Chb14jomm08C}}|title=Descriptive Physical Oceanography: An Introduction|isbn=978-0750645522|year=2011|publisher=Elsevier Inc.|location=Oxford UK}}</ref> While internal waves generally have a lower frequency than surface waves, they often form as a single wave that breaks into multiple waves as it hits a slope and moves upward.<ref name="Helfrich 1992">{{cite journal|author1-link=Karl Helfrich|last=Helfrich|first=K.|title=Internal solitary wave breaking and run-up on a uniform slope|journal=Journal of Fluid Mechanics|year=1992|volume=243|pages=133–154|doi=10.1017/S0022112092002660|doi-broken-date=2 November 2024 |bibcode = 1992JFM...243..133H |s2cid=122915102 }}</ref> This vertical breakup of internal waves causes significant diapycnal mixing and turbulence.<ref name="Gregg 1989">{{cite journal|last=Gregg|first=M.|title=Scaling turbulent dissipation in the thermocline|journal=Journal of Geophysical Research|year=1989|volume=94|issue=C7|series=9686–9698|doi=10.1029/JC094iC07p09686|page=9686|bibcode=1989JGR....94.9686G}}</ref><ref name="Taylor 1992">{{cite journal|last=Taylor|first=J.|title=The energetics of breaking events in a resonantly forced internal wave field|journal=Journal of Fluid Mechanics|year=1992|volume=239|pages=309–340|doi=10.1017/S0022112092004427|doi-broken-date=2 November 2024 |bibcode = 1992JFM...239..309T |s2cid=121973787 }}</ref> Internal waves can act as nutrient pumps, bringing plankton and cool nutrient-rich water to the surface.<ref name="Leichter et al. 1996"/><ref name="Leichter et al. 1998"/><ref name="Andrews and Gentien 1982">{{cite journal|last=Andrews|first=J.|author2=Gentien P.|title=Upwelling as a source of nutrients for the Great Barrier Reef ecosystems: A solution to Darwin's question?|journal=Marine Ecology Progress Series|year=1982|volume=8|pages=257–269|doi=10.3354/meps008257|bibcode=1982MEPS....8..257A|doi-access=free}}</ref><ref name="Sandstrom and Elliott 1984">{{cite journal|last=Sandstrom|first=H.|author2=Elliott J.|title=Internal tide and solitons on the Scotian shelf: A nutrient pump at work|journal=Journal of Geophysical Research|year=1984|volume=89|issue=C4|pages=6415–6426|doi=10.1029/JC089iC04p06415|bibcode=1984JGR....89.6415S}}</ref><ref name="Wolanski and Hamner 1988">{{cite journal|last=Wolanski|first=E.|author2=Hamner W. |title=Topographically controlled fronts in the ocean and their biological significance|journal=Science|year=1988|volume=241|pages=177–181|doi=10.1126/science.241.4862.177|pmid=17841048|issue=4862|bibcode = 1988Sci...241..177W |s2cid=19757639}}</ref><ref name="Rougerie et al. 1992">{{cite journal|last=Rougerie|first=F.|author2=Fagerstrom J.|author3=Andrie C.|title=Geothermal endo-upwelling: A solution to the reef nutrient paradox?|journal=Continental Shelf Research|year=1992|volume=12|pages=785–798|doi=10.1016/0278-4343(92)90044-K|issue=7–8|bibcode = 1992CSR....12..785R |url=http://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_6/b_fdi_33-34/36720.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_6/b_fdi_33-34/36720.pdf |archive-date=2022-10-09 |url-status=live}}</ref><ref name="Wolanski and Delesalle 1993">{{cite journal|last=Wolanski|first=E.|author2=Delesalle B.|title=Upwelling by internal waves, Tahiti, French Polynesia|journal=Continental Shelf Research|year=1993|volume=15|pages=357–368|doi=10.1016/0278-4343(93)E0004-R|issue=2–3|bibcode = 1995CSR....15..357W }}</ref><ref name="Szmant and Forrester 1996">{{Cite journal | last1 = Szmant | first1 = A. M. | last2 = Forrester | first2 = A. | doi = 10.1007/BF01626075 | title = Water column and sediment nitrogen and phosphorus distribution patterns in the Florida Keys, USA | journal = Coral Reefs | volume = 15 | issue = 1 | pages = 21–41 | year = 1996 |bibcode = 1996CorRe..15...21S | s2cid = 42822848 }}</ref><ref name="Furnas and Mitchell 1996">{{Cite journal | last1 = Furnas | first1 = M. J. | last2 = Mitchell | first2 = A. W. | doi = 10.1016/0278-4343(95)00060-7 | title = Nutrient inputs into the central Great Barrier Reef (Australia) from subsurface intrusions of Coral Sea waters: A two-dimensional displacement model | journal = Continental Shelf Research | volume = 16 | issue = 9 | pages = 1127–1148 | year = 1996 |bibcode = 1996CSR....16.1127F }}</ref><ref name="Leichter and Miller 1999">{{cite journal|last=Leichter|first=J.|author2=Miller S.|title=Predicting high-frequency upwelling: Spatial and temporal patterns of temperature anomalies on a Florida coral reef |year=1999|volume=19|issue=7|pages=911–928|doi=10.1016/s0278-4343(99)00004-7|journal=Continental Shelf Research|bibcode=1999CSR....19..911L}}</ref><ref name="Leichter et al. 2003">{{cite journal|last=Leichter|first=J.|author2=Stewart H.|author3=Miller S.|s2cid=15125174|title=Episodic nutrient transport to Florida coral reefs|journal=Limnology and Oceanography|year=2003|volume=48|pages=1394–1407|doi=10.4319/lo.2003.48.4.1394|issue=4|bibcode=2003LimOc..48.1394L}}</ref> | |||
Corals also absorb nutrients, including inorganic nitrogen and phosphorus, directly from water. Many corals extend their tentacles at night to catch ] that brush them when the water is agitated. Zooplankton provide the polyp with nitrogen, and the polyp shares some of the nitrogen with the zooxanthellae, which also require this element.<ref name="Castro">Castro, Peter and Michael Huber. 2000. ''Marine Biology.'' 3rd ed. Boston: McGraw-Hill.</ref> The varying pigments in different species of zooxanthellae give them an overall brown or golden-brown appearance, and give brown corals their colors. Other pigments such as reds, blues, greens, etc. come from colored proteins made by the coral animals. Coral which loses a large fraction of its zooxanthellae becomes white (or sometimes pastel shades in corals that are richly pigmented with their own colorful proteins) and is said to be ], a condition which, unless corrected, can kill the coral. | |||
Sponges are another key to explaining Darwin’s paradox. They live in crevices in the coral reefs. They are efficient ]s, and in the ] they consume about 60% of the phytoplankton that drifts by. The sponges eventually excrete nutrients in a form the corals can use.<ref>{{cite web |url=http://news.nationalgeographic.com/news/2001/11/1107_keyholecoral.html |title=Rich Coral Reefs in Nutrient-Poor Water: Paradox Explained? |first=John |last=Roach |publisher=] |date=November 7, 2001 |accessdate=April 5, 2011}}</ref> | |||
] | ] | ||
The irregular structure characteristic of coral reef bathymetry may enhance mixing and produce pockets of cooler water and variable nutrient content.<ref name="Leichter et al. 2005">{{cite journal |last=Leichter|first=J. |author2=Deane G.|author3=Stokes M.|title=Spatial and Temporal Variability of Internal Wave Forcing on a Coral Reef|journal=Journal of Physical Oceanography|year=2005|volume=35 |issue=11|pages=1945–1962|doi=10.1175/JPO2808.1 |bibcode=2005JPO....35.1945L |s2cid=52498621 |url=https://cloudfront.escholarship.org/dist/prd/content/qt3c97637x/qt3c97637x.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://cloudfront.escholarship.org/dist/prd/content/qt3c97637x/qt3c97637x.pdf |archive-date=2022-10-09 |url-status=live}}</ref> Arrival of cool, nutrient-rich water from depths due to internal waves and tidal bores has been linked to growth rates of suspension feeders and benthic algae<ref name="Leichter et al. 1998" /><ref name="Leichter et al. 2003" /><ref name="Smith et al. 2004">{{cite journal|last=Smith|first=J.|author2=Smith C.|author3=Vroom P.|author4=Beach K.|author5=Miller S.|title=Nutrient and growth dynamics of Halimeda tuna on Conch Reef, Florida Keys: Possible influence of internal tides on nutrient status and physiology|journal=Limnology and Oceanography|year=2004|volume=49|issue=6|pages=1923–1936|doi=10.4319/lo.2004.49.6.1923 |bibcode=2004LimOc..49.1923S|doi-access=free}}</ref> as well as plankton and larval organisms.<ref name="Leichter et al. 1998" /><ref name="Pineda 1994">{{cite journal|last=Pineda|first=J.|title=Internal tidal bores in the nearshore: Warm-water fronts, seaward gravity currents and the onshore transport of neustonic larvae|journal=]|year=1994|volume=52|issue=3|pages=427–458 |doi=10.1357/0022240943077046}}</ref> The seaweed ] reacts to deep water nutrient sources because their tissues have different concentrations of nutrients dependent upon depth.<ref name="Leichter et al. 2003" /> Aggregations of eggs, larval organisms and plankton on reefs respond to deep water intrusions.<ref name="Wolanski and Hamner 1988" /> Similarly, as internal waves and bores move vertically, surface-dwelling larval organisms are carried toward the shore.<ref name="Pineda 1994" /> This has significant biological importance to cascading effects of food chains in coral reef ecosystems and may provide yet another key to unlocking the paradox. | |||
The roughness of coral surfaces is the key to coral survival in agitated waters. Normally, a boundary layer of still water surrounds a submerged object, which acts as a barrier. Waves breaking on the extremely rough edges of corals disrupt the boundary layer, allowing the corals access to passing nutrients. Turbulent water thereby promotes reef growth and branching. Without the nutritional gains brought by rough coral surfaces, even the most effective recycling would leave corals wanting in nutrients.<ref>{{cite journal |url=http://www.newscientist.com/article/mg17523612.100-corals-play-rough-over-darwins-paradox.html |title=Corals play rough over Darwin's paradox |first=Rachel |last2=Nowak |issue=2361 |journal=] date=21 September 2002 }}</ref> | |||
] provide soluble ]s |
] provide soluble ]s via ].<ref>{{cite journal | last1 = Wilson | first1 = E | year = 2004 | title = Coral's Symbiotic Bacteria Fluoresce, Fix Nitrogen | url = http://pubs.acs.org/cen/news/8233/8233notw7.html | journal = Chemical and Engineering News | volume = 82 | issue = 33| page = 7 | doi = 10.1021/cen-v082n033.p007a }}</ref> | ||
Coral reefs |
Coral reefs often depend on surrounding habitats, such as ]s and ]s, for nutrients. Seagrass and mangroves supply dead plants and animals that are rich in nitrogen and serve to feed fish and animals from the reef by supplying wood and vegetation. Reefs, in turn, protect mangroves and seagrass from waves and produce ] in which the mangroves and seagrass can root.<ref name="Greenpeace">{{cite book |url={{google books |plainurl=y |id=Pik3MQAACAAJ}}|title=Greenpeace Book of Coral Reefs |first1=Sue |last1=Wells |first2=Nick |last2=Hanna | publisher=Sterling Publishing Company |year=1992 | isbn=978-0-8069-8795-8 }}</ref> | ||
{{clear}} | {{clear}} | ||
==Biodiversity== | ==Biodiversity== | ||
{{multiple image | |||
]es, ]es and ]s]] | |||
| align = right | |||
] | |||
| direction = vertical | |||
| width = 220 | |||
| image1 = Callyspongia sp. (Tube sponge).jpg | |||
| alt1 = | |||
| caption1 = Tube sponges attracting ]es, ]es and ]s | |||
| image2 = Underwater World.jpg | |||
| alt2 = | |||
| caption2 = Over 4,000 species of fish inhabit coral reefs. | |||
| image3 = Coral reef PloS.jpg | |||
| alt3 = | |||
| caption3 = Organisms can cover every square inch of a coral reef. | |||
}} | |||
Coral reefs form some of the world's most productive ecosystems, providing complex and varied ]s that support a wide range of organisms.<ref name="BarnesMann1991AquaticEcology">{{cite book | title=Fundamentals of Aquatic Ecology|author1=Barnes, R.S.K. |author2=Mann, K.H. | publisher=Blackwell Publishing| year=1991| isbn=978-0-632-02983-9| pages=217–227| url={{google books |plainurl=y |id=mOZZlzgdTrwC|page=227}}}}</ref><ref name="Fuchs">{{cite journal| author=Fuchs. T| url=http://library.queensu.ca/ojs/index.php/ISE/article/view/4627| title=Effects of Coral Reef Complexity on Invertebrate Biodiversity| journal=Immediate Science Ecology Publishing| year=2013| pages=1–10| url-status=dead| archive-date=April 2, 2015| archive-url=https://web.archive.org/web/20150402153213/http://library.queensu.ca/ojs/index.php/ISE/article/view/4627}}</ref> ]s just below ] level have a mutually beneficial relationship with ] forests at high tide level and ] meadows in between: the reefs protect the mangroves and seagrass from strong currents and waves that would damage them or ] the sediments in which they are rooted, while the mangroves and sea grass protect the coral from large influxes of ], fresh water and ]. This level of variety in the environment benefits many coral reef animals, which, for example, may feed in the sea grass and use the reefs for protection or breeding.<ref>{{cite book |author1=Hatcher, B.G. |author2=Johannes, R.E. |author3=Robertson, A.J. |chapter=Conservation of Shallow-water Marine Ecosystems |title=Oceanography and Marine Biology: An Annual Review |volume=27 |publisher=Routledge |year=1989 |isbn=978-0-08-037718-6 |chapter-url={{google books |plainurl=y |id=XpmNqFaDZ7cC|page=320}} |page=320}}</ref> | |||
Coral reefs form some of the world's most productive ecosystems, providing complex and varied ]s that support a wide range of other organisms.<ref name="BarnesMann1991AquaticEcology">{{cite book | |||
| title=Fundamentals of Aquatic Ecology| author=Barnes, R.S.K., and Mann, K.H. | |||
| publisher=Blackwell Publishing| year=1991| isbn=0-632-02983-8| pages=217–227 | |||
| url=http://books.google.com/?id=mOZZlzgdTrwC&pg=PA227| accessdate=2008-11-26 | |||
}}</ref> ]s just below ] level also have a mutually beneficial relationship with ] forests at high tide level and ] meadows in between: the reefs protect the mangroves and seagrass from strong currents and waves that would damage them or ] the sediments in which they are rooted, while the mangroves and sea grass protect the coral from large influxes of ], fresh water and ]. This additional level of variety in the environment is beneficial to many types of coral reef animals, which, for example, may feed in the sea grass and use the reefs for protection or breeding.<ref>{{cite book | |||
| author=Hatcher, B.G. Johannes, R.E., and Robertson, A.J.| chapter=Conservation of Shallow-water Marine Ecosystems | |||
| title=Oceanography and Marine Biology: An Annual Review: Volume 27| publisher=Routledge| year=1989| isbn=0-08-037718-1 | |||
| url=http://books.google.com/?id=XpmNqFaDZ7cC&pg=PA320 | |||
| accessdate=2008-11-21|page=320 | |||
}}</ref> | |||
Reefs are home to a |
Reefs are home to a variety of animals, including fish, ]s, ], ]ns (which includes some types of corals and ]), ]s, ]s (including ], ], ]s and ]s), ]s (including ]s), ]s (including ], ]s and ]s), ]s, ]s and ]s. Aside from humans, ]s are rare on coral reefs, with visiting ]s such as ]s the main exception. A few species feed directly on corals, while others graze on algae on the reef.<ref name="Spalding" /><ref name="Castro" /> Reef biomass is positively related to species diversity.<ref>{{cite journal |url=https://www.sciencedaily.com/releases/2011/04/110405130347.htm |title=World's Reef Fishes Tussling With Human Overpopulation |journal=ScienceDaily |date=April 5, 2011}}</ref> | ||
|url=http://www.sciencedaily.com/releases/2011/04/110405130347.htm | |||
|title=World's Reef Fishes Tussling With Human Overpopulation | |||
|journal=ScienceDaily |date=Apr. 5, 2011 |accessdate=April 25, 2011}}</ref> | |||
The same hideouts in a reef may be regularly inhabited by different species at different times of day. Nighttime predators such as ] and ] hide during the day, while ], ], ], ]s and ] hide from ]s and ]s.<ref name=murph/>{{rp|49}} | |||
===Fish=== | |||
{{main|Coral reef fish}} | |||
Over 4,000 species of fish inhabit coral reefs.<ref name="Spalding" /> The reasons for this diversity remain controversial. Hypotheses include the "lottery", in which the first (lucky winner) recruit to a territory is typically able to defend it against latecomers, "competition", in which adults compete for territory, and less-competitive species must be able to survive in poorer habitat, and "predation", in which population size is a function of postsettlement piscivore mortality.<ref>{{cite web |url=http://www.marinebiology.org/fishecology.htm |first= Jason |last=Buchheim |publisher=marinebiology.org |title=Coral Reef Fish Ecology |accessdate=April 5, 2011}}</ref> Healthy reefs can produce up to 35 tons of fish per square kilometer each year, but damaged reefs produce much less.<ref name="McClellan">{{cite web | |||
|last1=McClellan |first1=Kate |last2=Bruno |first2=John|year=2008|url=http://www.eoearth.org/article/Coral_degradation_through_destructive_fishing_practices | |||
|title=Coral degradation through destructive fishing practices |publisher=Encyclopedia of Earth |accessdate= October 25, 2008}}</ref> | |||
The great number and diversity of hiding places in coral reefs, i.e. ], are the most important factor causing the great diversity and high ] of the organisms in coral reefs.<ref name="GratwickeSpeight2005">{{cite journal|last1=Gratwicke|first1=B.|last2=Speight|first2=M. R.|title=The relationship between fish species richness, abundance and habitat complexity in a range of shallow tropical marine habitats|journal=Journal of Fish Biology|volume=66|issue=3|year=2005|pages=650–667|issn=0022-1112|doi=10.1111/j.0022-1112.2005.00629.x|bibcode=2005JFBio..66..650G }}</ref><ref name="FontanetoSanciangco2013">{{cite journal|last1=Fontaneto|first1=Diego|last2=Sanciangco|first2=Jonnell C.|last3=Carpenter|first3=Kent E.|last4=Etnoyer|first4=Peter J.|last5=Moretzsohn|first5=Fabio|title=Habitat Availability and Heterogeneity and the Indo-Pacific Warm Pool as Predictors of Marine Species Richness in the Tropical Indo-Pacific|journal=PLOS ONE|volume=8|issue=2|year=2013|pages=e56245|issn=1932-6203|doi=10.1371/journal.pone.0056245|pmid=23457533|pmc=3574161|bibcode=2013PLoSO...856245S|doi-access=free}}</ref> | |||
Reef species include: | |||
*Fish that influence the coral feed either on small animals living near the coral, seaweed/algae, or on the coral itself. Fish that feed on small animals include '']'' (]) who notably feed on organisms that inhabit larger fish, bullet fish{{Citation needed|date=April 2011}}<!-- can't find it in fishbase, etc. --> and sea-urchin-eating '']'' (triggerfish), while ]-eating fish include the '']'' (damselfishes). '']'' (groupers) cultivate the seaweed by removing creatures feeding on it (such as sea urchins), and they remove inedible seaweeds.<!-- by eating it? --> Fish that eat coral itself include '']'' (parrotfish) and '']'' (butterflyfish). {{Citation needed|date=April 2011}} | |||
Coral reefs also have a very high degree of microorganism diversity compared to other environments.<ref>{{Cite journal |last1=Galand |first1=Pierre E. |last2=Ruscheweyh |first2=Hans-Joachim |last3=Salazar |first3=Guillem |last4=Hochart |first4=Corentin |last5=Henry |first5=Nicolas |last6=Hume |first6=Benjamin C. C. |last7=Oliveira |first7=Pedro H. |last8=Perdereau |first8=Aude |last9=Labadie |first9=Karine |last10=Belser |first10=Caroline |last11=Boissin |first11=Emilie |last12=Romac |first12=Sarah |last13=Poulain |first13=Julie |last14=Bourdin |first14=Guillaume |last15=Iwankow |first15=Guillaume |date=2023-06-01 |title=Diversity of the Pacific Ocean coral reef microbiome |journal=Nature Communications |language=en |volume=14 |issue=1 |pages=3039 |doi=10.1038/s41467-023-38500-x |pmid=37264002 |pmc=10235103 |bibcode=2023NatCo..14.3039G |issn=2041-1723|hdl=20.500.11850/616066 |hdl-access=free }}</ref> | |||
*Fish that cruise the boundaries of the reef or nearby seagrass meadows include predators, such as '']''(]s), ]s, ]s, certain types of ], ]s and '']'' (snappers). ] and plankton-eating fish also populate reefs. Seagrass-eating fish include horse mackerel, snapper, '']'' (porgies) and '']'' (grunts). Plankton-eating fish include ''Caesio'' (]), ], ], and the ] '']'' (squirrelfish), '']'' (cardinalfish) and '']'' (lanternfish).{{Citation needed|date=April 2011}} | |||
===Algae=== | |||
Fish that swim in coral reefs can be as colorful as the reef. Examples are the parrotfish, '']'' (angelfish), damselfish, '']'' (blennies) and butterflyfish. At night, some change to a less vivid color.{{Citation needed|date=April 2011}} | |||
Reefs are chronically at risk of algal encroachment. Overfishing and excess nutrient supply from onshore can enable algae to outcompete and kill the coral.<ref>{{cite web |title=Coral Reef Biology |url=http://www.coral.noaa.gov/component/content/article/138.html |access-date=April 6, 2011 |archive-url=https://web.archive.org/web/20110927181624/http://www.coral.noaa.gov/component/content/article/138.html |archive-date=September 27, 2011 |url-status=dead |publisher=]}}</ref><ref>{{cite book |last=Glynn |first=P.W. |year=1990 |title=Ecosystems of the World v. 25-Coral Reefs |editor-first=Z. |editor-last=Dubinsky |publisher=Elsevier Science |location=New York |isbn=978-0-444-87392-7}}</ref> Increased nutrient levels can be a result of sewage or chemical fertilizer runoff. Runoff can carry nitrogen and phosphorus which promote excess algae growth. Algae can sometimes out-compete the coral for space. The algae can then smother the coral by decreasing the oxygen supply available to the reef.<ref>{{Cite journal|last1=Murphy|first1=James W.A. |last2=Richmond|first2=Robert H.|date=2016-04-19 |title=Changes to coral health and metabolic activity under oxygen deprivation|journal=PeerJ|volume=4 |pages=e1956|doi=10.7717/peerj.1956|pmid=27114888|pmc=4841221|issn=2167-8359 |doi-access=free }}</ref> Decreased oxygen levels can slow down calcification rates, weakening the coral and leaving it more susceptible to disease and degradation.<ref>{{cite web|title=THE EFFECTS OF TERRESTRIAL RUNOFF OF SEDIMENTS, NUTRIENTS AND OTHER POLLUTANTS ON CORAL REEFS|url=http://coralreefs.org/wp-content/uploads/2014/05/ISRS-Briefing-Paper-3-Water-Quality.pdf|access-date=2015-12-05|url-status=dead|archive-date=March 4, 2016|archive-url=https://web.archive.org/web/20160304091903/http://coralreefs.org/wp-content/uploads/2014/05/ISRS-Briefing-Paper-3-Water-Quality.pdf}}</ref> Algae inhabit a large percentage of surveyed coral locations.<ref>{{Cite journal |title=Algae-Dominated Reefs |first1=Peter S. |last1=Vroom| first2=Kimberly N. |last2=Page |first3=Jean C. |last3=Kenyon |first4=Russell E. |last4=Brainard |journal=American Scientist |year=2006 |volume=94 |issue=5 |pages=430–437|doi=10.1511/2006.61.1004}}</ref> The algal population consists of ], ] and ]. Some sea urchins (such as '']'') eat these algae and could thus decrease the risk of algal encroachment. | |||
=== |
===Sponges=== | ||
Sponges are essential for the functioning of the coral reef system. Algae and corals in coral reefs produce organic material. This is filtered through sponges which convert this organic material into small particles which in turn are absorbed by algae and corals. Sponges are essential to the coral reef system however, they are quite different from corals. While corals are complex and many celled while sponges are very simple organisms with no tissue. They are alike in that they are both immobile aquatic invertebrates but otherwise are completely different. | |||
Sea urchins, ] and ] eat seaweed. Some species of sea urchins, such as '']'', can play a pivotal part in preventing algae from overrunning reefs.<ref>{{cite book | |||
| last = Osborne | |||
| first = Patrick L. | |||
| title = Tropical Ecosystem and Ecological Concepts | |||
| publisher = Cambridge University Press | |||
| year = 2000 | |||
| location = Cambridge | |||
| page = 464 | |||
| isbn = 0-521-64523-9}} | |||
</ref> ] and ]s eat sponges. | |||
'''Types of sponges-''' | |||
A number of invertebrates, collectively called '''cryptofauna''', inhabit the coral skeletal substrate itself, either boring into the skeletons (through the process of ]) or living in pre-existing voids and crevices. Those animals boring into the rock include sponges, ] mollusks, and ]ns. Those settling on the reef include many other species, particularly crustaceans and ] worms.<ref name="Nybakken" /> | |||
There are several different species of sea sponge. They come in multiple shapes and sizes and all have unique characteristics. Some types of sea sponges include; the tube sponge, vase sponge, yellow sponge, bright red tree sponge, painted tunicate sponge, and the sea squirt sponge. | |||
===Algae=== | |||
Reefs are chronically at risk of algal encroachment. Overfishing and excess nutrient supply from onshore can enable algae to outcompete and kill the coral.<ref>{{cite web |url=http://www.coral.noaa.gov/component/content/article/138.html |title=Coral Reef Biology |publisher=] |accessdate=April 6, 2011}}</ref><ref>{{cite book |last=Glynn |first=P.W. |year=1990 |title=Ecosystems of the World v. 25-Coral Reefs |editor-first=Z. |editor-last=Dubinsky |publisher=Elsevier Science |location=New York, NY |isbn=978-0-444-87392-7}}</ref> In surveys done around largely uninhabited US Pacific islands, algae inhabit a large percentage of surveyed coral locations.<ref>{{Cite journal | title=Algae-Dominated Reefs | first1=Peter S. | last1=Vroom| first2=Kimberly N. | last2=Page | first3=Jean C. | last3=Kenyon | first4=Russell E. |last4=Brainard | journal=American Scientist | year=2006 | volume=94 | issue=5 | pages=430–437|doi=10.1511/2006.61.1004}}</ref> The algae population consists of ], ], and ]. | |||
'''Medicinal Qualities of Sea Sponges-''' | |||
Sea sponges have provided the base for many life saving medications. Scientists began to study them in the 1940s and after a few years, discovered that sea sponges contain properties that can stop viral infections. The first drug developed from sea sponges was released in 1969. | |||
===Fish=== | |||
{{main|Coral reef fish}} | |||
Over 4,000 species of fish inhabit coral reefs.<ref name="Spalding" /> The reasons for this diversity remain unclear. Hypotheses include the "lottery", in which the first (lucky winner) recruit to a territory is typically able to defend it against latecomers, "competition", in which adults compete for territory, and less-competitive species must be able to survive in poorer habitat, and "predation", in which population size is a function of postsettlement piscivore mortality.<ref>{{cite web |url=http://www.marinebiology.org/fishecology.htm |first= Jason |last=Buchheim |publisher=marinebiology.org |title=Coral Reef Fish Ecology |access-date=April 5, 2011}}</ref> Healthy reefs can produce up to 35 tons of fish per square kilometre each year, but damaged reefs produce much less.<ref name="McClellan">{{cite web |last1=McClellan |first1=Kate |last2=Bruno |first2=John|year=2008|url=http://www.eoearth.org/article/Coral_degradation_through_destructive_fishing_practices | |||
|title=Coral degradation through destructive fishing practices |publisher=Encyclopedia of Earth |access-date= October 25, 2008}}</ref> | |||
===Invertebrates=== | |||
Sea urchins, '']'' and ] eat seaweed. Some species of sea urchins, such as '']'', can play a pivotal part in preventing algae from overrunning reefs.<ref>{{cite book | |||
| last = Osborne | first = Patrick L. |url={{google books |plainurl=y |id=EwPwPHDM-YsC}}| title = Tropical Ecosystem and Ecological Concepts | publisher = Cambridge University Press | year = 2000 | location = Cambridge | page = 464 | isbn = 978-0-521-64523-2}}</ref> Researchers are investigating the use of native collector urchins, '']'', for their potential as biocontrol agents to mitigate the spread of invasive algae species on coral reefs.<ref name="Westbrook-2015">{{Cite journal|last1=Westbrook|first1=Charley E.|last2=Ringang|first2=Rory R.|last3=Cantero|first3=Sean Michael A.|last4=Toonen|first4=Robert J.|last5=Team|first5=HDAR & TNC Urchin|date=2015-09-15|title=Survivorship and feeding preferences among size classes of outplanted sea urchins, Tripneustes gratilla, and possible use as biocontrol for invasive alien algae|journal=PeerJ|language=en|volume=3|pages=e1235|doi=10.7717/peerj.1235|pmid=26401450|pmc=4579015|issn=2167-8359 |doi-access=free }}</ref><ref>{{Cite journal|last1=Conklin|first1=Eric J.|last2=Smith|first2=Jennifer E.|date=2005-11-01|title=Abundance and Spread of the Invasive Red Algae, Kappaphycus spp., in Kane'ohe Bay, Hawai'i and an Experimental Assessment of Management Options|journal=Biological Invasions|language=en|volume=7|issue=6|pages=1029–1039|doi=10.1007/s10530-004-3125-x|bibcode=2005BiInv...7.1029C |s2cid=33874352|issn=1387-3547}}</ref> '']'' and ]s eat sponges. | |||
A number of invertebrates, collectively called "cryptofauna", inhabit the coral skeletal substrate itself, either boring into the skeletons (through the process of ]) or living in pre-existing voids and crevices. Animals boring into the rock include sponges, ] mollusks, and ]ns. Those settling on the reef include many other species, particularly crustaceans and ] worms.<ref name="Nybakken" /> | |||
===Seabirds=== | ===Seabirds=== | ||
Coral reef systems provide important habitats for ] species, some endangered. For example, ] in ] supports nearly three million seabirds, including two-thirds (1.5 million) of the global population of ], and one-third of the global population of ].<ref>. The.honoluluadvertiser.com ( |
Coral reef systems provide important habitats for ] species, some endangered. For example, ] in ] supports nearly three million seabirds, including two-thirds (1.5 million) of the global population of ], and one-third of the global population of ].<ref> {{Webarchive|url=https://web.archive.org/web/20161227143504/http://the.honoluluadvertiser.com/article/2005/Jan/17/ln/ln23p.html |date=27 December 2016 }}. The.honoluluadvertiser.com (January 17, 2005). Retrieved on November 1, 2011.</ref> Each seabird species has specific sites on the atoll where they nest. Altogether, 17 species of seabirds live on Midway. The ] is the rarest, with fewer than 2,200 surviving after excessive feather hunting in the late 19th century.<ref>{{cite web|title=U.S. Fish & Wildlife Service – Birds of Midway Atoll |url=http://www.fws.gov/midway/midwaywildlifebirds.html |access-date=August 19, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20130522041619/http://www.fws.gov/midway/midwaywildlifebirds.html |archive-date=May 22, 2013 }}</ref> | ||
| title = U.S. Fish & Wildlife Service – Birds of Midway Atoll | |||
| url = http://www.fws.gov/midway/midwaywildlifebirds.html | |||
| accessdate = August 19, 2009}} | |||
</ref> | |||
===Other=== | ===Other=== | ||
]s feed exclusively on fish and their eggs.<ref>{{cite book|last=Heatwole|first=Harold|url={{google books |plainurl=y |id=lSgWAQAAIAAJ}}|title=Sea snakes|year=1999|publisher=Krieger|location=Malabar, Fla|isbn=978-1-57524-116-6|edition=2.}}</ref><ref>{{cite journal|last=Li|first=Min|author2=Fry, B.G. |author3=Kini, R. Manjunatha |title=Eggs-Only Diet: Its Implications for the Toxin Profile Changes and Ecology of the Marbled Sea Snake (Aipysurus eydouxii)|journal=Journal of Molecular Evolution|date=1 January 2005|volume=60|issue=1|pages=81–89|doi=10.1007/s00239-004-0138-0|pmid=15696370|bibcode=2005JMolE..60...81L|s2cid=17572816}}</ref><ref>{{cite journal|last=Voris|first=Harold K.|title=Fish Eggs as the Apparent Sole Food Item for a Genus of Sea Snake, Emydocephalus (Krefft)|journal=Ecology|date=1 January 1966|volume=47|issue=1|pages=152–154|doi=10.2307/1935755|jstor=1935755|bibcode=1966Ecol...47..152V }}</ref> Marine birds, such as ]s, ]s, ]s and ], feed on reef fish. Some land-based ]s intermittently associate with reefs, such as ]s, the ] and semiaquatic snakes, such as '']''. ]s, particularly ]s, feed on sponges.<ref name="Sea turtle loss">{{cite journal|last=McClenachan|first=Loren|author2=Jackson, Jeremy BC |author3=Newman, Marah JH |title=Conservation implications of historic sea turtle nesting beach loss|journal=Frontiers in Ecology and the Environment|date=1 August 2006|volume=4|issue=6|pages=290–296 |doi=10.1890/1540-9295(2006)42.0.co;2}}</ref><ref>{{cite book |last1=Lutz |first1=Peter L. |url= {{google books |plainurl=y |id=QNRBDwAAQBAJ}} |title=The biology of sea turtles |year=1996 |publisher=CRC Press |location=Boca Raton, Fla|isbn=978-0849384226 |last2=Musick |first2=John A.}}</ref><ref>{{cite journal |last=Meylan |first=Anne |title=Spongivory in Hawksbill Turtles: A Diet of Glass |journal= Science |date=January 22, 1988 |volume=239 |issue=4838 |pages= 393–395 |doi= 10.1126/science.239.4838.393 |pmid= 17836872 |bibcode= 1988Sci...239..393M |s2cid=22971831 }}</ref> | |||
]s feed exclusively on fish and their eggs. Tropical birds, such as ]s, ]s, ]s and ], feed on reef fish. Some land-based ]s intermittently associate with reefs, such as ]s, the ] and semiaquatic snakes, such as '']''. ]s eat sponges.{{citation needed|date=December 2010}} | |||
<gallery mode="packed"> | |||
<gallery> | |||
File:Prionurus laticlavius.jpg|] ] | File:Prionurus laticlavius.jpg|] ] | ||
File:Caribbean reef squid.jpg|] | File:Caribbean reef squid.jpg|] | ||
File:Stenopus hispidus (high res).jpg|] | File:Stenopus hispidus (high res).jpg|] | ||
File:Triaenodon obesus moc.jpg| |
File:Triaenodon obesus moc.jpg|] | ||
File:Green turtle John Pennekamp.jpg|] | File:Green turtle John Pennekamp.jpg|] | ||
File:Red sea-reef 3627.jpg|] | File:Red sea-reef 3627.jpg|] | ||
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</gallery> | </gallery> | ||
== |
==Ecosystem services== | ||
Coral reefs deliver ] to tourism, fisheries and coastline protection. The global economic value of coral reefs has been estimated to be between US$29.8 billion<ref name=Cesar>{{cite book |last=Cesar |first=H.J.S. |url= {{google books |plainurl=y |id=WicVAQAAIAAJ}} |title=The Economics of Worldwide Coral Reef Degradation |year=2003 |publisher=Cesar Environmental Economics Consulting |location=The Netherlands |page=4 |author2=Burke, L. |author3=Pet-Soede, L. |access-date=21 September 2013}} (pdf: )</ref> and $375 billion per year.<ref name=Costanza>{{cite journal |last=Costanza |first=Robert |author2=Ralph d'Arge |author3=Rudolf de Groot |author4= Stephen Farber |author5=Monica Grasso |author6=Bruce Hannon |author7=Karin Limburg |author8=Shahid Naeem |author9=Robert V. O'Neill |author10=Jose Paruelo |author11=Robert G. Raskin |author12=Paul Sutton |author13=Marjan van den Belt |title= The value of the world's ecosystem services and natural capital |journal=Nature |date=15 May 1997 |volume=387 |pages=253–260 |doi= 10.1038/387253a0 |issue=6630 |bibcode= 1997Natur.387..253C |s2cid=672256 |url=https://discovery.ucl.ac.uk/id/eprint/10189378/ }}</ref> About 500 million people benefit from ecosystem services provided by coral reefs.<ref>{{cite journal |doi=10.1146/annurev-environ-012320-083019|doi-access=free|title=The Impacts of Ocean Acidification on Marine Ecosystems and Reliant Human Communities|year=2020|last1=Doney|first1=Scott C. |last2=Busch|first2=D. Shallin|last3=Cooley|first3=Sarah R.|last4=Kroeker|first4=Kristy J. |journal=Annual Review of Environment and Resources|volume=45|pages=83–112}}</ref> | |||
Coral reefs deliver ] to tourism, fisheries and coastline protection. The global economic value of coral reefs has been estimated at as much as $US375 billion per year.<ref>{{cite web |url=http://www.noaanews.noaa.gov/stories2010/20101115_coralbleaching.html |title=Heat Stress to Caribbean Corals in 2005 Worst on Record |publisher=] |date=15 November 2010 |accessdate=April 7, 2011}}</ref> Coral reefs protect shorelines by absorbing wave energy, and many small islands would not exist without their reef to protect them. According to the ] ], the economic cost over a 25 year period of destroying one km of coral reef is somewhere between $137,000 and $1,200,000.<ref name=WWF>{{cite web |url=http://www.worldwildlife.org/what/wherewework/coraltriangle/importance-of-coral.html |title=The Importance of Coral to People |publisher=] |accessdate=April 7, 2011}}</ref> About six million tons of fish are taken each year from coral reefs. Well-managed coral reefs have an annual yield of 15 tons seafood on average per square kilometer. Southeast Asia's coral reef fisheries alone yield about $ 2.4 billion annually from seafood.<ref name=WWF /> | |||
The economic cost over a 25-year period of destroying one square kilometre of coral reef has been estimated to be somewhere between $137,000 and $1,200,000.<ref name="WWF">{{cite web |url=http://www.worldwildlife.org/what/wherewework/coraltriangle/importance-of-coral.html|title=The Importance of Coral to People|publisher=]|access-date=April 7, 2011 |archive-url=https://web.archive.org/web/20100710032307/http://www.worldwildlife.org/what/wherewework/coraltriangle/importance-of-coral.html |archive-date=2010-07-10 |url-status=dead}}</ref> | |||
To improve the management of coastal coral reefs, another environmental group, the ] (WRI) developed and published tools for calculating the value of coral reef-related tourism, shoreline protection and fisheries, partnering with five Caribbean countries. As of April 2011, published working papers covered St. Lucia, Tobago, Belize, and the Dominican Republic, with a paper for Jamaica in preparation. The WRI was also "making sure that the study results support improved coastal policies and management planning".<ref>{{cite web |title=Coastal Capital: Economic Valuation of Coastal Ecosystems in the Caribbean |publisher=] |url=http://www.wri.org/project/valuation-caribbean-reefs}}</ref> The Belize study estimated the value of reef and mangrove services at 395–559 million dollars annually.<ref>{{cite web |url=http://pdf.wri.org/coastal_capital_belize_brochure.pdf |title=Coastal Capital: Belize: The Economic Contribution of Belize’s Coral Reefs and Mangroves |first1=Emily |last1=Cooper |first2=Lauretta |last2=Burke |first3=Nadia |last3=Bood |year=2008 |accessdate=April 6, 2011}}</ref> | |||
To improve the management of coastal coral reefs, the ] (WRI) developed and published tools for calculating the value of coral reef-related tourism, shoreline protection and fisheries, partnering with five Caribbean countries. As of April 2011, published working papers covered ], ], ], and the ]. The WRI was "making sure that the study results support improved coastal policies and management planning".<ref>{{cite web|url=http://www.wri.org/project/valuation-caribbean-reefs|title=Coastal Capital: Economic Valuation of Coastal Ecosystems in the Caribbean|date=19 February 2014 |publisher=]}}</ref> The Belize study estimated the value of reef and mangrove services at $395–559 million annually.<ref>{{cite web|url=http://pdf.wri.org/coastal_capital_belize_brochure.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://pdf.wri.org/coastal_capital_belize_brochure.pdf |archive-date=2022-10-09 |url-status=live|title=Coastal Capital: Belize: The Economic Contribution of Belize's Coral Reefs and Mangroves|last1=Cooper|first1=Emily|last2=Burke|first2=Lauretta |year=2008|access-date=April 6, 2011|last3=Bood|first3=Nadia}}</ref> | |||
Bermuda's coral reefs provide economic benefits to the Island worth on average $722 million per year, based on six key ecosystem services, according to Sarkis ''et al'' (2010).<ref>{{cite web |url=http://media.wix.com/ugd/addae3_b2c263862f2843c3aadc9bacf0317ec1.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://media.wix.com/ugd/addae3_b2c263862f2843c3aadc9bacf0317ec1.pdf |archive-date=2022-10-09 |url-status=live|title=Total Economic Value of Bermuda's Coral Reefs. Valuation of ecosystem Services|last1=Sarkis|first1=Samia|last2=van Beukering|first2=Pieter J.H. |year=2010|access-date=May 29, 2015|last3=McKenzie |first3=Emily}}</ref> | |||
===Shoreline protection=== | |||
]. The ] are part of the mesoamerican coral reef system. Due to this, the authorities have made huge investments for its preservation.]] | |||
Coral reefs protect shorelines by absorbing wave energy, and many small islands would not exist without reefs. Coral reefs can reduce wave energy by 97%, helping to prevent loss of life and property damage. Coastlines protected by coral reefs are also more stable in terms of erosion than those without. Reefs can attenuate waves as well as or better than artificial structures designed for ] such as breakwaters.<ref>{{cite journal |last1=Ferarrio|display-authors=et al |first1=F. |title=The effectiveness of coral reefs for coastal hazard risk reduction and adaptation. |journal=Nature Communications |date=2014 |volume=5 |page=3794 |doi=10.1038/ncomms4794 |pmid=24825660 |pmc=4354160 |bibcode=2014NatCo...5.3794F }}</ref> An estimated 197 million people who live both below 10 m elevation and within 50 km of a reef consequently may receive risk reduction benefits from reefs. Restoring reefs is significantly cheaper than building artificial breakwaters in tropical environments. Expected damages from flooding would double, and costs from frequent storms would triple without the topmost meter of reefs. For 100-year storm events, flood damages would increase by 91% to $US 272 billion without the top meter.<ref>{{cite journal |last1=Beck, M.|display-authors=et al |title=The global flood protection savings provided by coral reefs |journal=Nature Communications |date=2018 |volume=9 |issue=1 |page=2186 |doi=10.1038/s41467-018-04568-z|pmid=29895942 |pmc=5997709 |bibcode=2018NatCo...9.2186B }}</ref> | |||
===Fisheries=== | |||
About six million tons of fish are taken each year from coral reefs. Well-managed reefs have an average annual yield of 15 tons of seafood per square kilometre. Southeast Asia's coral reef fisheries alone yield about $2.4 billion annually from seafood.<ref name="WWF" /> | |||
==Threats== | ==Threats== | ||
] off ], ]<ref name="Coral reefs around the world">{{cite news | |
] off ], ]<ref name="Coral reefs around the world">{{cite news |date=September 2, 2009 |title=Coral reefs around the world |work=] |url=https://www.theguardian.com/environment/interactive/2009/sep/02/coral-world-interactive}}</ref>]] | ||
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{{See also|Environmental issues with coral reefs|Coral bleaching|Environmental threats to the Great Barrier Reef}} | ||
] in Australia]] | |||
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Since their emergence 485 million years ago, coral reefs have faced many threats, including disease,<ref>{{cite book |last1=Peters |first1=Esther C. |title=Coral Reefs in the Anthropocene |chapter=Diseases of Coral Reef Organisms |date=2015 |pages=147–178 |doi=10.1007/978-94-017-7249-5_8 |publisher=Springer Netherlands |language=en|isbn=978-94-017-7248-8 }}</ref> predation,<ref>{{cite journal |last1=Bradbury |first1=R. H. |last2=Hammond |first2=L. S. |last3=Moran |first3=P. J. |last4=Reichelt |first4=R. E. |title=Coral reef communities and the crown-of-thorns starfish: Evidence for qualitatively stable cycles |journal=Journal of Theoretical Biology |date=7 March 1985 |volume=113 |issue=1 |pages=69–80 |doi=10.1016/S0022-5193(85)80076-X |bibcode=1985JThBi.113...69B |issn=0022-5193}}</ref> invasive species, ] by grazing fish,<ref>{{cite journal |last=Hutchings |first=P.A. |title=Biological destruction of coral reefs |doi=10.1007/BF00298083 |journal=Coral Reefs |volume=12 |issue=1 |pages=1–17 |year=1986 |bibcode=1986CorRe...4..239H|s2cid=34046524 }}</ref> ]s, and ]. Recent human activities present new threats. From 2009 to 2018, coral reefs worldwide declined 14%.<ref>{{Cite web|last=Visser|first=Nick|date=2021-10-05|title=Planet Lost Startling Amount Of Coral Reefs In 10 Years, Report Finds|url=https://www.huffpost.com/entry/planet-coral-reefs-lost-10-years_n_615bdcd5e4b099230d273a1f|url-status=live|access-date=2021-10-05|website=HuffPost|language=en|archive-url=https://web.archive.org/web/20211005112753/https://www.huffpost.com/entry/planet-coral-reefs-lost-10-years_n_615bdcd5e4b099230d273a1f |archive-date=5 October 2021 }}</ref> | |||
Coral reefs are dying around the world.<ref name="Coral reefs around the world"/> In particular, coral mining, agricultural and urban runoff, ] (organic and inorganic), ], ], disease, and the digging of ]s and access into islands and bays are localized threats to coral ecosystems. Broader threats are sea temperature rise, sea level rise and ] changes from ], all associated with ] emissions. In 2011, researchers suggested that "extant marine invertebrates face the same synergistic effects of multiple stressors" that occurred during the ], and that genera "with poorly buffered respiratory physiology and calcareous shells", such as corals, were particularly vulnerable.<ref>Clapham ME and Payne JL (2011) ''Geology'', '''39''' (11): 1059–1062. {{doi|10.1130/G32230.1}}</ref><ref>Payne JL and Clapham ME (2012) ''Annual Review of Earth and Planetary Sciences'', '''40''': 89–111. {{doi|10.1146/annurev-earth-042711-105329}}</ref><ref> ''New York Times'', 30 April 2012.</ref> | |||
Human activities that threaten coral include coral mining, ],<ref>{{cite journal |last1=Clark |first1=Malcolm R. |last2=Tittensor |first2=Derek P. |title=An index to assess the risk to stony corals from bottom trawling on seamounts |journal=Marine Ecology |date=2010 |volume=31 |issue=s1 |pages=200–211 |doi=10.1111/j.1439-0485.2010.00392.x |bibcode=2010MarEc..31..200C |language=en |issn=1439-0485|doi-access=free }}</ref> and the digging of ]s and accesses into islands and bays, all of which can damage marine ecosystems if not done sustainably. Other localized threats include ], ], coral overmining,<ref>{{cite journal |last1=Caras |first1=Tamir |last2=Pasternak |first2=Zohar |title=Long-term environmental impact of coral mining at the Wakatobi marine park, Indonesia |journal=Ocean & Coastal Management |date=1 October 2009 |volume=52 |issue=10 |pages=539–544 |doi=10.1016/j.ocecoaman.2009.08.006 |bibcode=2009OCM....52..539C |issn=0964-5691}}</ref> and ], including use of the banned ] ] ]; although absent in developed countries, these activities continue in places with few environmental protections or poor regulatory enforcement.<ref>{{cite news |title=Blast fishing |url=https://stopillegalfishing.com/issues/blast-fishing/ |website=Stop Illegal Fishing |access-date=15 November 2019}}</ref><ref>{{cite web |title=Magnuson-Stevens Act: A unique charge for sustainable seafood {{!}} National Oceanic and Atmospheric Administration |url=https://www.noaa.gov/explainers/magnuson-stevens-act-unique-charge-for-sustainable-seafood |website=www.noaa.gov |access-date=15 November 2019}}</ref><ref>{{cite web |title=Coral |url=https://www.fws.gov/international/animals/coral.html |publisher=US Fish and Wildlife Service |access-date=15 November 2019 |archive-date=29 May 2020 |archive-url=https://web.archive.org/web/20200529020151/https://www.fws.gov/international/animals/coral.html |url-status=dead }}</ref> Chemicals in sunscreens may awaken latent viral infections in zooxanthellae<ref name="Sunscreen" /> and impact reproduction.<ref>{{Cite news|url=https://www.scientificamerican.com/article/why-is-hawaii-banning-sunscreen/|title=Why Is Hawaii Banning Sunscreen?|last=Stierwalt|first=Everyday Einstein Sabrina|work=Scientific American|access-date=2018-08-19|language=en}}</ref> However, concentrating tourism activities via offshore platforms has been shown to limit the spread of coral disease by tourists.<ref>{{cite journal|last=Lamb|first=Joleah |author2=Bette Willis|title=Using coral disease prevalence to assess the effects of concentrating tourism activities on offshore reefs in a tropical marine park|journal=Conservation Biology|date=August 16, 2011|volume=25 |issue=5|pages=1044–1052|doi=10.1111/j.1523-1739.2011.01724.x|pmid=21848962|bibcode=2011ConBi..25.1044L |s2cid=12979332 |doi-access=free}}</ref> | |||
In El Nino-year 2010, preliminary reports show global coral bleaching reached its worst level since another El Nino year, 1998, when 16% of the world's reefs died as a result of increased water temperature. In Indonesia's ] province, surveys showed some 80% of bleached corals died. Scientists don’t yet understand the long-term impacts of coral bleaching, but they do know that bleaching leaves corals vulnerable to disease, stunts their growth, and affects their reproduction, while severe bleaching kills them.<ref>. Blogs.ei.columbia.edu. Retrieved on 2011-11-01.</ref> In July, ] closed several dive sites where virtually all the corals were damaged by bleaching.<ref name=ritter>{{cite news | |||
| title=Climate goal may spell end for some coral reefs | |||
| date=December 8, 2010 | |||
| url=http://www.physorg.com/news/2010-12-climate<sup>−</sup>goal-coral-reefs.html | |||
| first=Karl | |||
| last=Ritter | |||
| agency=Associated Press | |||
| accessdate=December, 2010}}</ref><ref name="natgeo2006" >{{cite web | |||
|title=Global Warming Has Devastating Effect on Coral Reefs, Study Shows | |||
|first=Sean |last=Markey | |||
|publisher=National Geographic News | |||
|date=May 16, 2006}}</ref> | |||
] emissions present a broader threat through sea temperature rise and sea level rise, resulting in widespread ] and loss of coral cover.<ref>{{cite web|title=Caribbean coral reefs may disappear within 20 years: Report |url=http://news.biharprabha.com/2014/07/caribbean-coral-reefs-may-disappear-within-20-years-report/|work=IANS|publisher=news.biharprabha.com|access-date=3 July 2014}}</ref> ] causes more frequent and more severe storms, also changes ocean circulation patterns, which can destroy coral reefs.<ref></ref>] also affects corals by decreasing calcification rates and increasing dissolution rates, although corals can ] their calcifying fluids to changes in ] pH and ] to mitigate the impact.<ref>{{cite journal |last1=McCulloch |first1=Malcolm T. |last2=D'Olivo |first2=Juan Pablo |last3=Falter |first3=James |last4=Holcomb |first4=Michael |last5=Trotter |first5=Julie A. |title=Coral calcification in a changing World and the interactive dynamics of pH and DIC upregulation |journal=Nature Communications |date=30 May 2017 |volume=8 |issue=1 |page=15686 |doi=10.1038/ncomms15686 |pmid=28555644 |pmc=5499203 |bibcode=2017NatCo...815686M |language=en |issn=2041-1723}}</ref><ref>Cooley, S., D. Schoeman, L. Bopp, P. Boyd, S. Donner, D.Y. Ghebrehiwet, S.-I. Ito, W. Kiessling, P. Martinetto, E. Ojea, M.-F. Racault, B. Rost, and M. Skern-Mauritzen, 2022: . In: . Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 379–550, doi:10.1017/9781009325844.005.</ref> Volcanic and human-made aerosol pollution can modulate regional sea surface temperatures.<ref>{{cite journal |last1=Kwiatkowski |first1=Lester |last2=Cox |first2=Peter M. |last3=Economou |first3=Theo |last4=Halloran |first4=Paul R. |last5=Mumby |first5=Peter J. |last6=Booth |first6=Ben B. B. |last7=Carilli |first7=Jessica |last8=Guzman |first8=Hector M. |title=Caribbean coral growth influenced by anthropogenic aerosol emissions |journal=Nature Geoscience |date=May 2013 |volume=6 |issue=5 |pages=362–366 |doi=10.1038/ngeo1780 |bibcode=2013NatGe...6..362K |language=en |issn=1752-0908}}</ref> | |||
To find answers for these problems, researchers study the various factors that impact reefs. The list includes the ocean's role as a ], atmospheric changes, ], ocean acidification, ]es, impacts of ] carrying agents to far flung reefs, pollutants, ]s and others. Reefs are threatened well beyond coastal areas.{{citation needed|date=December 2010}} | |||
In 2011, two researchers suggested that "extant marine invertebrates face the same synergistic effects of multiple stressors" that occurred during the ], and that genera "with poorly buffered respiratory physiology and calcareous shells", such as corals, were particularly vulnerable.<ref>{{cite journal|author=Clapham ME and Payne|doi=10.1130/G32230.1|title=Acidification, anoxia, and extinction: A multiple logistic regression analysis of extinction selectivity during the Middle and Late Permian|year=2011|journal=Geology|volume=39|issue=11|pages=1059–1062|bibcode = 2011Geo....39.1059C }}</ref><ref>{{cite journal|vauthors=Payne JL, Clapham ME|doi=10.1146/annurev-earth-042711-105329|title=End-Permian Mass Extinction in the Oceans: An Ancient Analog for the Twenty-First Century?|year=2012|journal=Annual Review of Earth and Planetary Sciences|volume=40 |issue=1|pages=89–111|bibcode = 2012AREPS..40...89P }}</ref><ref> ''New York Times'', April 30, 2012.</ref> | |||
General estimates show approximately 10% of the world's coral reefs are dead.<ref name="Kleypas, J.A. 2006">{{Cite document |last1=Kleypas |first1=J.A. |first2=R.A. |last2=Feely |first3=V.J. |last3=Fabry |first4=C. |last4=Langdon |first5=C.L. |last5=Sabine |first6=L.L. |last7=Robbins |year=2006 |title=Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A guide for Future Research |publisher=], ], & ] |url=http://www.ucar.edu/communications/Final_acidification.pdf |accessdate=April 7, 2011 }}</ref><ref>Save Our Seas, 1997 Summer Newsletter, Dr. Cindy Hunter and Dr. Alan Friedlander</ref><ref>{{cite book |chapter=Status of Coral Reefs, Coral Reef Monitoring and Management in Southeast Asia, 2004 |last1=Tun |first1=K. |first2=L.M. |last2=Chou |first3=A. |last3=Cabanban |first4=V.S. |last4=Tuan |last5=Philreefs |first6=T. |last6=Yeemin |last7=Suharsono |first8=K. |last8=Sour |first9=D. |last9=Lane |year=2004 |pages=235–276 |editor-first=C. |editor-last=Wilkinson |title=Status of Coral Reefs of the world: 2004 |publisher=Australian Institute of Marine Science |location=Townsville, Queensland, Australia}}</ref> About 60% of the world's reefs are at risk due to destructive, human-related activities. The threat to the health of reefs is particularly strong in ], where 80% of reefs are ].{{citation needed|date=December 2010}} By the 2030s, 90% of reefs are expected to be at risk from both human activities and ]; by 2050, ''all'' coral reefs will be in danger. <ref>{{cite web |url=http://pdf.wri.org/reefs_at_risk_revisited_executive_summary.pdf |title=Reefs at Risk Revisited |publisher=World Resources Institute| date=February 2011| accessdate=March 16, 2012}}</ref> | |||
Corals respond to stress by "bleaching", or expelling their colorful ]te ]s. Corals with Clade C zooxanthellae are generally vulnerable to heat-induced bleaching, whereas corals with the hardier Clade A or D are generally resistant,<ref>{{Cite journal |last1=Abrego |first1=D. |last2=Ulstrup |first2=K. E |last3=Willis |first3=B. L |last4=van Oppen |first4=M. J.H |date=2008-10-07 |title=Species-specific interactions between algal endosymbionts and coral hosts define their bleaching response to heat and light stress |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=275 |issue=1648 |pages=2273–2282 |doi=10.1098/rspb.2008.0180 |pmid=18577506 |pmc=2603234 |issn=0962-8452}}</ref> as are tougher coral genera like ] and ].<ref name=Guest2012/> | |||
Current research is showing that ecotourism in the ] is contributing to coral disease.<ref>{{cite journal|last=Lamb|first=Joleah|coauthors=Bette Willis|title=Using coral disease prevalence to assess the effects of concentrating tourism activities on offshore reefs in a tropical marine park|journal=Conservation Biology|date=August 16, 2011|year=2011|month=August|volume=25|issue=5|pages=1044-1052|url=http://onlinelibrary.wiley.com/doi/10.1111/j.1523-1739.2011.01724.x/abstract|doi=10.1111/j.1523-1739.2011.01724.x}}</ref> | |||
Every 4–7 years, an ] event causes some reefs with heat-sensitive corals to bleach,<ref name=Barkley2018/> with especially widespread bleachings in 1998 and 2010.<ref name=ritter>{{cite news | |||
{{clear}} | |||
|title = Climate goal may spell end for some coral reefs | |||
|date = December 8, 2010 | |||
|url = http://www.physorg.com/news/2010-12-climate<sup>−</sup>goal-coral-reefs.html | |||
|first = Karl | |||
|last = Ritter | |||
|agency = Associated Press | |||
}}{{dead link|date=December 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name="natgeo2006" >{{cite web | |||
|title=Global Warming Has Devastating Effect on Coral Reefs, Study Shows | |||
|first=Sean |last=Markey|url=http://news.nationalgeographic.com/news/2006/05/warming-coral.html | |||
|archive-url=https://web.archive.org/web/20060614171831/http://news.nationalgeographic.com/news/2006/05/warming-coral.html | |||
|url-status=dead | |||
|archive-date=14 June 2006 | |||
|publisher=National Geographic News | |||
|date=May 16, 2006}}</ref> However, reefs that experience a severe bleaching event become resistant to future heat-induced bleaching,<ref>{{cite journal |last1=Maynard |first1=J. A. |last2=Anthony |first2=K. R. N. |last3=Marshall |first3=P. A. |last4=Masiri |first4=I. |title=Major bleaching events can lead to increased thermal tolerance in corals |journal=Marine Biology |date=1 August 2008 |volume=155 |issue=2 |pages=173–182 |doi=10.1007/s00227-008-1015-y |bibcode=2008MarBi.155..173M |s2cid=85935124 |language=en |issn=1432-1793}}</ref><ref name=Thompson2009>{{cite journal |last1=Thompson |first1=D. M. |last2=van Woesik |first2=R. |title=Corals escape bleaching in regions that recently and historically experienced frequent thermal stress |journal=Proceedings of the Royal Society B: Biological Sciences |date=22 August 2009 |volume=276 |issue=1669 |pages=2893–2901 |doi=10.1098/rspb.2009.0591 |pmid=19474044 |pmc=2817205 }}</ref><ref name=Guest2012>{{cite journal |last1=Guest |first1=James R. |last2=Baird |first2=Andrew H. |last3=Maynard |first3=Jeffrey A. |last4=Muttaqin |first4=Efin |last5=Edwards |first5=Alasdair J. |last6=Campbell |first6=Stuart J. |last7=Yewdall |first7=Katie |last8=Affendi |first8=Yang Amri |last9=Chou |first9=Loke Ming |title=Contrasting Patterns of Coral Bleaching Susceptibility in 2010 Suggest an Adaptive Response to Thermal Stress |journal=PLOS ONE |date=9 March 2012 |volume=7 |issue=3 |pages=e33353 |doi=10.1371/journal.pone.0033353 |pmid=22428027 |pmc=3302856 |bibcode=2012PLoSO...733353G |language=en |issn=1932-6203|doi-access=free }}</ref> due to rapid ].<ref name=Thompson2009/> Similar rapid adaption may protect coral reefs from global warming.<ref>{{cite journal |last1=Matz |first1=Mikhail V. |last2=Treml |first2=Eric A. |last3=Aglyamova |first3=Galina V. |last4=Bay |first4=Line K. |title=Potential and limits for rapid genetic adaptation to warming in a Great Barrier Reef coral |journal=PLOS Genetics |date=19 April 2018 |volume=14 |issue=4 |pages=e1007220 |doi=10.1371/journal.pgen.1007220 |pmid=29672529 |pmc=5908067 |language=en |issn=1553-7404 |doi-access=free }}</ref> | |||
A large-scale systematic study of the ] coral community, which experienced ten El Niño-coincident ] events from 1960 to 2016, found that the reef recovered from almost complete death after severe events.<ref name=Barkley2018>{{Cite journal|last1=Barkley|first1=Hannah C.|last2=Cohen|first2=Anne L.|last3=Mollica|first3=Nathaniel R.|last4=Brainard|first4=Russell E.|last5=Rivera|first5=Hanny E.|last6=DeCarlo |first6=Thomas M.|last7=Lohmann|first7=George P.|last8=Drenkard|first8=Elizabeth J.|last9=Alpert|first9=Alice E.|date=2018-11-08|title=Repeat bleaching of a central Pacific coral reef over the past six decades (1960–2016) |journal=Communications Biology|language=En|volume=1|issue=1|pages=177|doi=10.1038/s42003-018-0183-7|pmid=30417118|pmc=6224388|issn=2399-3642}}</ref> | |||
==Protection== | ==Protection== | ||
{{Main|Coral reef protection}} | {{Main|Coral reef protection}} | ||
] | ] | ||
{{benthos sidebar|habitat}} | |||
] |
] (MPAs) are areas designated because they provide various kinds of protection to ocean and/or estuarine areas. They are intended to promote responsible ] and ]. MPAs can also encompass social and biological objectives, including reef restoration, aesthetics, biodiversity and economic benefits. | ||
|publisher=National Geographic Magazine |date=January 2011 |accessdate=April 30, 2011 | |||
|url=http://ngm.nationalgeographic.com/2011/01/phoenix-islands/stone-text}}</ref> | |||
The effectiveness of MPAs is still debated. For example, a study investigating the success of a small number of MPAs in ], the ] and ] found no significant differences between the MPAs and unprotected sites.<ref>{{cite journal |last1=McClanahan |first1=Timothy |last2=Marnane |first2=Michael |last3=Cinner |first3=Joshua E. |last4=Kiene |first4=William E. |title=A Comparison of Marine Protected Areas and Alternative Approaches to Coral-Reef Management |doi=10.1016/j.cub.2006.05.062 |pmid=16860739 |journal=Current Biology |volume=16 |issue=14 |pages=1408–13 |year=2006|s2cid=17105410 |doi-access=free |bibcode=2006CBio...16.1408M }}</ref><ref>{{cite journal |last=Christie |first=P. |title=Marine protected areas as biological successes and social failures in Southeast Asia |url=https://www.scopus.com/record/display.url?eid=2-s2.0-24344460900&origin=inward&txGid=D99709748F3514D3637554EEF14AEB58.53bsOu7mi7A1NSY7fPJf1g%3a7 |archive-url=https://archive.today/20131216072606/http://www.scopus.com/record/display.url?eid=2-s2.0-24344460900&origin=inward&txGid=D99709748F3514D3637554EEF14AEB58.53bsOu7mi7A1NSY7fPJf1g:7 |url-status=dead |archive-date=2013-12-16 |journal=American Fisheries Society Symposium |volume=2004 |issue=42 |pages=155–164 |year=2004 }}</ref> Furthermore, in some cases they can generate local conflict, due to a lack of community participation, clashing views of the government and fisheries, effectiveness of the area and funding.<ref>{{cite journal |last1=McClanahan |first1=Timothy |last2=Davies |first2=Jamie |last3=Maina |first3=Joseph |title=Factors influencing resource users and managers' perceptions towards marine protected area management in Kenya |journal=Environmental Conservation |volume=32 |pages=42–49 |doi=10.1017/S0376892904001791 |year=2005|issue=1 |bibcode=2005EnvCo..32...42M |s2cid=85105416 |url=https://zenodo.org/record/895731 }}</ref> In some situations, as in the ], MPAs provide revenue to locals. The level of income provided is similar to the income they would have generated without controls.<ref>{{cite magazine |title=Phoenix Rising |author=Stone, Gregory | |||
To help combat ocean acidification, there are some laws in place to reduce greenhouse gases like carbon dioxide. The Clean Water Act puts pressure on state government agencies to monitor and limit runoff of pollutants that can cause ocean acidification. There are also stormwater surge preventions in place, as well as coastal buffers between agricultural land and the coastline. This act also ensures that delicate watershed ecosystems are intact such as wetlands. The Clean Water Act is funded by the federal government, and is monitored by various watershed groups. There are also many land use laws that reduce CO2 emissions by limiting deforestation. Deforestation causes erosion, which releases a large amount of carbon stored in the soil which then flows into the ocean, contributing to ocean acidification. There are also incentives to reduce miles traveled by vehicles, which reduces the carbon emissions into the atmosphere, therefore reducing the amount of dissolved CO2 in the ocean. State and federal governments also control coastal erosion, which releases stored carbon in the soil into the ocean, increasing ocean acidification <ref>{{cite journal |last=Kelly |first=R.P|first2=et al |year=2011 |title=Mitigating local causes of ocean acidification with existing laws |journal=Science |volume=332 |pages=1036-1037 }}</ref> | |||
|magazine=National Geographic Magazine |date=January 2011|url=https://www.nationalgeographic.com/magazine/article/phoenix-islands}}</ref> Overall, it appears the MPA's can provide protection to local coral reefs, but that clear management and sufficient funds are required. | |||
The Caribbean Coral Reefs – Status Report 1970–2012, states that coral decline may be reduced or even reversed. For this ] needs to be stopped, especially fishing on ], such as ]. Direct human pressure on coral reefs should also be reduced and the inflow of ] should be minimised. Measures to achieve this could include restricting coastal settlement, development and ]. The report shows that healthier reefs in the Caribbean are those with large, healthy populations of parrotfish. These occur in countries that protect parrotfish and other species, like ]. They also often ban ]ping and ]. Together these measures help creating "resilient reefs".<ref name="IUCNvideo">{{cite web|last1=Ewa Magiera|last2=Sylvie Rockel|title=From despair to repair: Dramatic decline of Caribbean corals can be reversed|url=http://www.iucn.org/?16056/From-despair-to-repair-Dramatic-decline-of-Caribbean-corals-can-be-reversed|access-date=8 June 2015|ref=]|date=2 July 2014}}</ref><ref>{{cite web|url=http://cmsdata.iucn.org/downloads/caribbean_coral_reefs___status_report_1970_2012.pdf|title=Caribbean Coral Reefs – Status Report 1970-2012|date=2013|website=IUCN.org|archive-url=https://web.archive.org/web/20150111013808/http://cmsdata.iucn.org/downloads/caribbean_coral_reefs___status_report_1970_2012.pdf|archive-date=January 11, 2015|url-status=dead}}</ref> | |||
], ], ] and ] status can protect reefs. For example, Belize's Barrier reef, ], ], the ] islands, ], ], ] and ] are world heritage sites.{{Citation needed|date=April 2011}} | |||
Protecting networks of diverse and healthy reefs, not only climate ], helps ensure the greatest chance of ], which is critical for coral to adapt to new climates.<ref name="Nature Research-2019">{{Cite journal|author1=Walsworth, T.E. |author2=Schindler, D.E. |author3=Colton, M.A. |author4=Webster, M.S. |author5=Palumbi, S.R. |author6=Mumby, P.J. |author7=Essington, T.E. |author8=Pinsky, M.L. |date=July 1, 2019|title=Management for network diversity speeds evolutionary adaptation to climate change|url=https://www.nature.com/articles/s41558-019-0518-5.epdf?author_access_token=P8wTmOVZpLkKcslba2guA9RgN0jAjWel9jnR3ZoTv0MfsDpsr-XFeaym1-pv8WErp3wvwWdkVHp-xxQar4ROnGw5GpCATCYx5cv3yLdU3H0Yd0zwLASpSOCiN5WSFidDI_GNaKqZ7ZiaG4o1CQ6xdw%3D%3D|journal=Nature Research|volume=9|pages=632–636}}</ref> A variety of conservation methods applied across marine and terrestrial threatened ecosystems makes coral adaption more likely and effective.<ref name="Nature Research-2019" /> | |||
In Australia, the Great Barrier Reef is protected by the ], and is the subject of much legislation, including a biodiversity action plan.{{Citation needed|date=April 2011}}. They have compiled a Coral Reef Resilience Action Plan. This detailed action plan consists of numerous adaptive management strategies including reducing our carbon footprint, which would ultimately reduce the amount of ocean acidification in the oceans surrounding the Great Barrier Reef. There’s also an extensive public awareness plan in place, providing education on the “rainforests of the sea” and how we can reduce our carbon emissions, therefore reducing ocean acidification <ref name="Great Barrier Reef Marine Park Authority">{{cite website|year=2007 |title=Great Barrier Reef Climate Change Action Plan 2007-2011 |website= Great Barrier Reef Marine Park Authority | url = http://www.gbrmpa.gov.au/__data/assets/pdf_file/0020/4493/climate-change-action-plan-2007-2012.pdf }}</ref> | |||
Designating a reef as a ], ], ] or ] site can offer protections. For example, Belize's barrier reef, ], the ] islands, ], ], ] and ] are world heritage sites.<ref>{{cite web|title=World Heritage List|url=https://whc.unesco.org/en/list/|website=UNESCO|access-date=18 December 2016}}</ref> | |||
Inhabitants of Ahus Island, ], ], have followed a generations-old practice of restricting fishing in six areas of their reef lagoon. Their cultural traditions allow line fishing, but not net or ]. The result is both the ] and individual fish sizes are significantly larger than in places where fishing is unrestricted.<ref>{{cite journal |last=Cinner |first=Joshua E. |first2=Michael J.|last2= MARNANE |first3=Tim R.|last3= McClanahan |year=2005 |title=Conservation and community benefits from traditional coral reef management at Ahus Island, Papua New Guinea |journal=Conservation Biology |volume=19 |issue=6 |pages=1714–1723 |doi=10.1111/j.1523-1739.2005.00209.x-i1}}</ref><ref>{{cite web| url=http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17182 |title=Coral Reef Management, Papua New Guinea |publisher = ]'s ]|accessdate=2 November 2006}}</ref> | |||
In Australia, the Great Barrier Reef is protected by the ], and is the subject of much legislation, including a biodiversity action plan.<ref>{{cite web |title=A biodiversity strategy for the Great Barrier Reef|publisher=Great Barrier Reef Marine Park Authority |url=http://www.gbrmpa.gov.au/outlook-for-the-reef/great-barrier-reef-outlook-report/outlook-online?sq_content_src=%2BdXJsPWh0dHAlM0ElMkYlMkZ3d3ctcmMuZ2JybXBhLmdvdi5hdSUyRl9fZGF0YSUyRmFzc2V0cyUyRnBkZl9maWxlJTJGMDAwNCUyRjQ1NjI1JTJGQW1lbmRlZF9CaW9kaXZlcnNpdHlfU3RyYXRlZ3lfX1JSX1BNY0dfMjAwODEwX0ZpbmFsLnBkZiZhbGw9MQ%3D%3D |access-date=20 September 2013|url-status=dead |archive-date=2012-03-17 |archive-url=https://web.archive.org/web/20120317092051/http://www.gbrmpa.gov.au/outlook-for-the-reef/great-barrier-reef-outlook-report/outlook-online?sq_content_src=%2BdXJsPWh0dHAlM0ElMkYlMkZ3d3ctcmMuZ2JybXBhLmdvdi5hdSUyRl9fZGF0YSUyRmFzc2V0cyUyRnBkZl9maWxlJTJGMDAwNCUyRjQ1NjI1JTJGQW1lbmRlZF9CaW9kaXZlcnNpdHlfU3RyYXRlZ3lfX1JSX1BNY0dfMjAwODEwX0ZpbmFsLnBkZiZhbGw9MQ%3D%3D}}</ref> Australia compiled a Coral Reef Resilience Action Plan. This plan consists of ] strategies, including reducing carbon footprint. A public awareness plan provides education on the "rainforests of the sea" and how people can reduce carbon emissions.<ref>{{cite web |year=2007 |title=Great Barrier Reef Climate Change Action Plan 2007–2012 |publisher=Great Barrier Reef Marine Park Authority |location=Townsville, Australia |url=http://www.gbrmpa.gov.au/__data/assets/pdf_file/0020/4493/climate-change-action-plan-2007-2012.pdf |access-date=16 March 2012 |archive-date=28 February 2016 |archive-url=https://web.archive.org/web/20160228225734/http://www.gbrmpa.gov.au/__data/assets/pdf_file/0020/4493/climate-change-action-plan-2007-2012.pdf |url-status=dead}}</ref> | |||
Inhabitants of Ahus Island, ], ], have followed a generations-old practice of restricting fishing in six areas of their reef lagoon. Their cultural traditions allow line fishing, but no net or ]. Both ] and individual fish sizes are significantly larger than in places where fishing is unrestricted.<ref>{{cite journal |last1=Cinner |first1=Joshua E. |first2=Michael J.|last2= Marnane |first3=Tim R.|last3= McClanahan |year=2005 |title=Conservation and community benefits from traditional coral reef management at Ahus Island, Papua New Guinea |journal=Conservation Biology |volume=19 |issue=6 |pages=1714–1723 |doi=10.1111/j.1523-1739.2005.00209.x-i1|bibcode=2005ConBi..19.1714C |s2cid=83619557 }}</ref><ref>{{cite web |title=Coral Reef Management, Papua New Guinea |url=http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17182 |publisher=]'s ] |access-date=November 2, 2006 |archive-date=October 11, 2006 |archive-url=https://web.archive.org/web/20061011023923/http://earthobservatory.nasa.gov///Newsroom/NewImages/images.php3?img_id=17182 |url-status=dead}}</ref> | |||
Increased levels of atmospheric CO<sub>2</sub> contribute to ocean acidification, which in turn damages coral reefs. To help combat ocean acidification, several countries have put laws in place to reduce greenhouse gases such as carbon dioxide. Many land use laws aim to reduce CO<sub>2</sub> emissions by limiting deforestation. Deforestation can release significant amounts of CO<sub>2</sub> absent sequestration via active follow-up forestry programs. Deforestation can also cause erosion, which flows into the ocean, contributing to ocean acidification. Incentives are used to reduce miles traveled by vehicles, which reduces carbon emissions into the atmosphere, thereby reducing the amount of dissolved CO<sub>2</sub> in the ocean. State and federal governments also regulate land activities that affect coastal erosion.<ref>{{cite journal |last1=Kelly |first1=RP |last2=Foley |first2=MM |last3=Fisher |first3=WS |last4=Feely |first4=RA |last5=Halpern |first5=BS |last6=Waldbusser |first6=GG |last7=Caldwell |first7=MR |year=2011 |url=http://www.st.nmfs.noaa.gov/iwgoa/documents/Science-2011-Kelly-1036-7.pdf |title=Mitigating local causes of ocean acidification with existing laws |journal=Science |volume=332 |issue=6033 |pages=1036–1037 |doi=10.1126/science.1203815 |pmid=21617060 |s2cid=206533178 |bibcode=2011Sci...332.1036K |access-date=1 November 2013 |archive-date=9 October 2022 |archive-url=https://ghostarchive.org/archive/20221009/http://www.st.nmfs.noaa.gov/iwgoa/documents/Science-2011-Kelly-1036-7.pdf |url-status=dead }}</ref> High-end satellite technology can monitor reef conditions.<ref>{{Cite news |last1=Mallikarjun |first1=Y. |date=2014-12-10 |title=Satellites to assess coral reef health |newspaper=The Hindu |url=http://www.thehindu.com/sci-tech/technology/satellites-to-assess-coral-reef-health/article6679863.ece |access-date=2014-12-13}}</ref> | |||
The United States ] puts pressure on state governments to monitor and limit run-off of polluted water. | |||
==Restoration== | ==Restoration== | ||
{{see also|Aquaculture of coral|Artificial reef|Restoration ecology}}Coral reef restoration has grown in prominence over the past several decades because of the unprecedented reef die-offs around the planet. Coral stressors can include pollution, warming ocean temperatures, extreme weather events, and overfishing. With the deterioration of global reefs, fish nurseries, biodiversity, coastal development and livelihood, and natural beauty are under threat. Fortunately, researchers have taken it upon themselves to develop a new field, coral restoration, in the 1970s–1980s<ref>{{Cite web|title=Coral Restoration |work=Shark Research & Conservation Program (SRC) |publisher=University of Miami |url=https://sharkresearch.rsmas.miami.edu/research/projects/coral-restoration/|access-date=2020-05-03}}</ref> | |||
] | |||
{{see also|Aquaculture of coral|Artificial reef|Restoration ecology}} | |||
===Coral farming=== | |||
], also known as ''coral farming'' or ''coral gardening'', is showing promise as a potentially effective tool for restoring coral reefs, which have been declining around the world.<ref name="Horoszowski-Fridman">{{cite journal|author=Horoszowski-Fridman, YB, Izhaki, I & Rinkevich, B |year=2011|title=Engineering of coral reef larval supply through transplantation of nursery-farmed gravid colonies|journal=Journal of Experimental Marine Biology and Ecology|volume=399|issue=2|pages=162–166|doi=10.1016/j.jembe.2011.01.005}}</ref><ref name="Pomeroy">{{cite journal|author=Pomeroy, RS, Parks, JE and Balboa, CM |year=2006|title=Farming the reef: is aquaculture a solution for reducing fishing pressure on coral reefs?|journal=Marine Policy|volume=30|issue=2|pages=111–130|doi=10.1016/j.marpol.2004.09.001}}</ref><ref name="Rinkevich">{{cite journal|author=Rinkevich, B |year=2008|url=http://www.ocean.org.il/Eng/_documents/Management-of-coral-reefs.pdf |title=Management of coral reefs: We have gone wrong when neglecting active reef restoration|journal=Marine pollution bulletin|volume=56|issue=11|pages=1821–1824|doi=10.1016/j.marpolbul.2008.08.014}}</ref> The process bypasses the early growth stages of corals when they are most at risk of dying. Coral seeds are grown in nurseries then replanted on the reef.<ref name="Ferse">{{cite journal|author=Ferse, SCA |year=2010|doi=10.1111/j.1526-100X.2010.00682.x|title=Poor Performance of Corals Transplanted onto Substrates of Short Durability|journal= Restoration Ecology|volume= 18|issue= 4|pages=399–407}}</ref> Coral is farmed by coral farmers who live locally to the reefs and farm for reef ] or for income. | |||
] | |||
], also known as coral farming or coral gardening, is showing promise as a potentially effective tool for restoring coral reefs.<ref name="Horoszowski-Fridman">{{cite journal |vauthors=Horoszowski-Fridman YB, Izhaki I, Rinkevich B |year=2011 |title=Engineering of coral reef larval supply through transplantation of nursery-farmed gravid colonies |journal=Journal of Experimental Marine Biology and Ecology |volume=399 |issue=2 |pages=162–166 |doi=10.1016/j.jembe.2011.01.005|bibcode=2011JEMBE.399..162H }}</ref><ref name="Pomeroy">{{cite journal|vauthors=Pomeroy RS, Parks JE, Balboa CM |year=2006 |title=Farming the reef: is aquaculture a solution for reducing fishing pressure on coral reefs? |journal=Marine Policy |volume=30 |issue=2 |pages=111–130 |doi=10.1016/j.marpol.2004.09.001|bibcode=2006MarPo..30..111P }}</ref><ref name="Rinkevich">{{cite journal|author=Rinkevich, B |year=2008 |url=http://www.ocean.org.il/Eng/_documents/Management-of-coral-reefs.pdf |archive-url=https://web.archive.org/web/20130523175241/http://www.ocean.org.il/Eng/_documents/Management-of-coral-reefs.pdf |url-status=dead |archive-date=2013-05-23 |title=Management of coral reefs: We have gone wrong when neglecting active reef restoration |journal=Marine Pollution Bulletin |volume=56 |issue=11 |pages=1821–1824 |doi=10.1016/j.marpolbul.2008.08.014 |pmid=18829052 |bibcode=2008MarPB..56.1821R }}</ref> The "gardening" process bypasses the early growth stages of corals when they are most at risk of dying. Coral seeds are grown in nurseries, then replanted on the reef.<ref name="Ferse">{{cite journal |author=Ferse, S.C.A. |year=2010 |doi=10.1111/j.1526-100X.2010.00682.x |title=Poor Performance of Corals Transplanted onto Substrates of Short Durability |journal= Restoration Ecology |volume= 18 |issue= 4 |pages=399–407|bibcode=2010ResEc..18..399F |s2cid=83723761 }}</ref> Coral is farmed by coral farmers whose interests range from reef ] to increased income. Due to its straight forward process and substantial evidence of the technique having a significant effect on coral reef growth, coral nurseries became the most widespread and arguably the most effective method for coral restoration.<ref name="Lirman-2016">{{Cite journal|last1=Lirman|first1=Diego|last2=Schopmeyer|first2=Stephanie|date=2016-10-20|title=Ecological solutions to reef degradation: optimizing coral reef restoration in the Caribbean and Western Atlantic|journal=PeerJ|language=en|volume=4|pages=e2597|doi=10.7717/peerj.2597|pmid=27781176|pmc=5075686|issn=2167-8359 |doi-access=free }}</ref> | |||
] | |||
Coral gardens take advantage of a coral's natural ability to fragment and continuing to grow if the fragments are able to anchor themselves onto new substrates. This method was first tested by Baruch Rinkevich<ref>{{Cite journal|last=Rinkevich|first=Baruch|date=1995|title=Restoration Strategies for Coral Reefs Damaged by Recreational Activities: The Use of Sexual and Asexual Recruits|journal=Restoration Ecology|language=en|volume=3|issue=4|pages=241–251|doi=10.1111/j.1526-100X.1995.tb00091.x|bibcode=1995ResEc...3..241R |issn=1526-100X}}</ref> in 1995 which found success at the time. By today's standards, coral farming has grown into a variety of different forms, but still has the same goals of cultivating corals. Consequently, coral farming quickly replaced previously used transplantation methods or the act of physically moving sections or whole colonies of corals into a new area.<ref name="Lirman-2016" /> Transplantation has seen success in the past and decades of experiments have led to a high success and survival rate. However, this method still requires the removal of corals from existing reefs. With the current state of reefs, this kind of method should generally be avoided if possible. Saving healthy corals from eroding substrates or reefs that are doomed to collapse could be a major advantage of utilizing transplantation. | |||
Coral gardens generally take on the safe forms no matter where you go. It begins with the establishment of a nursery where operators can observe and care for coral fragments.<ref name="Lirman-2016" /> It goes without saying that nurseries should be established in areas that are going to maximize growth and minimize mortality. Floating offshore coral trees or even aquariums are possible locations where corals can grow. After a location has been determined, collection and cultivation can occur. | |||
Efforts to expand the size and number of coral reefs generally involve supplying substrate to allow more corals to find a home. Substrate materials include discarded vehicle tires, scuttled ships, subway cars, and formed concrete, such as ]. Reefs also grow unaided on marine structures such as ]s.{{Citation needed|date=April 2011}} In large restoration projects, propagated ] on substrate can be secured with metal pins, ] or ].<ref>. coralgarden.co.uk (2009-05-08). Retrieved on 2011-11-08.</ref> Needle and thread can also attach A-hermatype coral to substrate.<ref>. coralgarden.co.uk (2009-05-08). Retrieved on 2011-11-08.</ref> | |||
The major benefit of using coral farms is it lowers polyp and juvenile mortality rates. By removing predators and recruitment obstacles, corals are able to mature without much hindrance. However, nurseries cannot stop climate stressors. Warming temperatures or hurricanes can still disrupt or even kill nursery corals. | |||
Low-voltage ]s applied through seawater ] dissolved minerals onto ] structures. The resultant white carbonate (]) is the same mineral that makes up natural coral reefs. Corals rapidly colonize and grow at accelerated rates on these coated structures. The electrical currents also accelerate formation and growth of both chemical limestone rock and the skeletons of corals and other shell-bearing organisms. The vicinity of the ] and ] provides a high-] environment which inhibits the growth of competitive filamentous and fleshy algae. The increased growth rates fully depend on the accretion activity.<ref name="Sabater">{{cite journal |last1=Sabater |first1=Marlowe G. |last2=Yap |first2=Helen T. |year=2004 |title=Long-term effects of induced mineral accretion on growth, survival, and corallite properties of Porites cylindrica Dana |journal=Journal of Experimental Marine Biology and Ecology |volume=311 |pages=355–374 | doi = 10.1016/j.jembe.2004.05.013 |url = http://people.uncw.edu/szmanta/2006%20pdfs/21%20Mineral%20accretion/Sabater%20and%20Yap%202004%20long%20term%20growth%20w%20mineral%20accretion.pdf | format=PDF |issue=2 }}</ref> | |||
Technology is becoming more popular in the coral farming process. Teams from the Reef Restoration and Adaptation Program (RRAP) have trialled coral counting technology utilizing a prototype robotic camera. The camera uses ] and learning algorithms to detect and count individual coral babies and track their growth and health in real time. This technology, with research led by ], is intended to be used during annual coral ] events and will provide researchers with control that is not currently possible when mass-producing corals.<ref>{{Cite web |date=2023-01-09 |title=The game-changing robotics helping to grow new corals |url=https://www.barrierreef.org/news/news/the-game-changing-robotics-helping-to-grow-new-corals |access-date=2024-01-19 |website=Great Barrier Reef Foundation |language=en}}</ref> | |||
During accretion, the settled corals display an increased growth rate, size and density, but after the process is complete, growth rate and density return to levels comparable to natural growth, and are about the same size or slightly smaller.<ref name="Sabater"/> | |||
===Creating substrates=== | |||
One case study with coral reef restoration was on the island of Oahu in Hawaii. The University of Hawaii has come up with a Coral Reef Assessment and Monitoring Program (CRAMP) to help relocate and restore coral reefs in Hawaii. A boat channel on the island of Oahu to the Hawaii Institute of Marine Biology was overcrowded with coral reefs. There were also many areas of coral reef patches in the channel that has been damaged from past dredging in the channel. Dredging covers the existing corals with sand, and their larvae cannot build and thrive on sand, they can only build on to existing reefs. Because of this, the University of Hawaii decided to relocate some of the coral reef to a different transplant site. They transplanted them with the help of the United States Army Divers, to a relocation site relatively close to the channel. What they observed was that very little, if any, damage occurred to any of the colonies while they were being transported, and no mortality of coral reefs has been observed on the new transplant site, but they will be continuing to monitor the new transplant site to see how potential environmental impacts (i.e. ocean acidification) will harm the overall reef mortality rate. What they found while trying to attach the coral to the new transplant site was that the coral that was placed on hard rock is growing considerably well, and there’s even coral growth on the wires that attached the transplant corals to the transplant site. This gives new hope to future research on coral reef transplant sites. As a result of this coral restoration project, no environmental effects were seen from the transplantation process, no recreational activities were decreased, and no scenic areas were impacted by the project. This is a great example that coral transplantation and restoration can work and thrive under the right conditions, which means there may be hope for other damaged coral reefs <ref name="Jokeil P.L., Ku’ulei S.R.">{{cite website |last1=Jokeil |first1=P.L. |last2=Ku’lei |first2=S.R |year=2004 |title= Coral Relocation Project in Kaneohe Bay, Oahu, Hawaii: Report on Phase 1 |website=Univeristy of Hawaii | url = http://cramp.wcc.hawaii.edu/Downloads/Publications/TR_Coral_Relocation_Report_1.pdf}}</ref> | |||
] | |||
Efforts to expand the size and number of coral reefs generally involve supplying substrate to allow more corals to find a home. Substrate materials include discarded vehicle tires, scuttled ships, subway cars and formed concrete, such as ]. Reefs grow unaided on marine structures such as ]. In large restoration projects, propagated ] on substrate can be secured with metal pins, ] or ]. Needle and thread can also attach A-hermatype coral to substrate. | |||
] is a substrate produced by a patented process that runs low voltage ]s through seawater to cause dissolved minerals to precipitate onto ] structures. The resultant white carbonate (]) is the same mineral that makes up natural coral reefs. Corals rapidly colonize and grow at accelerated rates on these coated structures. The electrical currents also accelerate the formation and growth of both chemical limestone rock and the skeletons of corals and other shell-bearing organisms, such as oysters. The vicinity of the ] and ] provides a high-] environment which inhibits the growth of competitive filamentous and fleshy algae. The increased growth rates fully depend on the accretion activity. Under the influence of the electric field, corals display an increased growth rate, size and density. | |||
Another possibility for coral restoration is gene therapy. Through infecting coral with genetically modified bacteria, it may be possible to grow corals that are more resistant to climate change and other threats. <ref>{{cite web |url=http://www.scientificamerican.com/article.cfm?id=gene-therapy-help-corals-survive-climate-change |title=Gene Therapy Could Help Corals Survive Climate Change |publisher=Scientific American| date=February 29, 1020}}</ref> | |||
Simply having many structures on the ocean floor is not enough to form coral reefs. Restoration projects must consider the complexity of the substrates they are creating for future reefs. Researchers conducted an experiment near Ticao Island in the Philippines in 2013<ref name="Yanovski-2019">{{Cite journal|last1=Yanovski|first1=Roy|last2=Abelson|first2=Avigdor|date=2019-07-01|title=Structural complexity enhancement as a potential coral-reef restoration tool|url=http://www.sciencedirect.com/science/article/pii/S0925857419301144|journal=Ecological Engineering|language=en|volume=132|pages=87–93|doi=10.1016/j.ecoleng.2019.04.007|bibcode=2019EcEng.132...87Y |s2cid=146076500|issn=0925-8574}}</ref> where several substrates in varying complexities were laid in the nearby degraded reefs. Large complexity consisted of plots that had both a human-made substrates of both smooth and rough rocks with a surrounding fence, medium consisted of only the human-made substrates, and small had neither the fence or substrates. After one month, researchers found that there was a positive correlation between structure complexity and recruitment rates of larvae.<ref name="Yanovski-2019" /> The medium complexity performed the best with larvae favoring rough rocks over smooth rocks. Following one year of their study, researchers visited the site and found that many of the sites were able to support local fisheries. They came to the conclusion that reef restoration could be done cost-effectively and will yield long term benefits given they are protected and maintained.<ref name="Yanovski-2019" /> | |||
== Reefs in the past == | |||
] | |||
===Relocation=== | |||
Throughout ] history, from a few thousand years after hard skeletons were developed by marine organisms, there were almost always reefs. The times of maximum development were in the ] (513–501 ]), ] (416–359 Ma) and ] (359–299 Ma), owing to order ] ] corals, and ] (100–65 Ma) and all ] (23 Ma–present), owing to order ] corals. | |||
] | |||
One case study with coral reef restoration was conducted on the island of ] in ]. The ] operates a Coral Reef Assessment and Monitoring Program to help relocate and restore coral reefs in Hawaii. A boat channel from the island of Oahu to the ] on ] was overcrowded with coral reefs. Many areas of coral reef patches in the channel had been damaged from past dredging in the channel. | |||
Dredging covers corals with sand. Coral larvae cannot settle on sand; they can only build on existing reefs or compatible hard surfaces, such as rock or concrete. Because of this, the university decided to relocate some of the coral. They transplanted them with the help of ] divers, to a site relatively close to the channel. They observed little if any damage to any of the colonies during transport and no mortality of coral reefs was observed on the transplant site. While attaching the coral to the transplant site, they found that coral placed on hard rock grew well, including on the wires that attached the corals to the site. | |||
Not all reefs in the past were formed by corals: in the ] (542–513 Ma) resulted from calcareous ] and ] (small animals with conical shape, probably related to ]) and in the ] (100–65 Ma), when there also existed reefs formed by a group of ] called ]; one of the valves formed the main conical structure and the other, much smaller valve acted as a cap. | |||
No environmental effects were seen from the transplantation process, recreational activities were not decreased, and no scenic areas were affected. | |||
{{clear}} | |||
As an alternative to transplanting coral themselves, juvenile fish can also be encouraged to relocate to existing coral reefs by auditory simulation. In damaged sections of the Great Barrier Reef, loudspeakers playing recordings of healthy reef environments were found to attract fish twice as often as equivalent patches where no sound was played, and also increased species biodiversity by 50%. | |||
==See also== | |||
{{Portal box|Ecology}} | |||
* ] | |||
* ] | |||
* ] | |||
* ] | |||
===Heat-tolerant symbionts=== | |||
==Notes== | |||
Another possibility for coral restoration is gene therapy: inoculating coral with ], or naturally-occurring heat-tolerant varieties of coral symbiotes, may make it possible to grow corals that are more resistant to climate change and other threats.<ref>{{cite magazine |url=http://www.scientificamerican.com/article.cfm?id=gene-therapy-help-corals-survive-climate-change |title=Gene Therapy Could Help Corals Survive Climate Change |magazine=Scientific American| date=February 29, 2012}}</ref> Warming oceans are forcing corals to adapt to unprecedented temperatures. Those that do not have a tolerance for the elevated temperatures experience coral bleaching and eventually mortality. There is already research that looks to create genetically modified corals that can withstand a warming ocean. Madeleine J. H. van Oppen, James K. Oliver, Hollie M. Putnam, and Ruth D. Gates described four different ways that gradually increase in human intervention to genetically modify corals.<ref name="van Oppen-2015">{{Cite journal|last1=van Oppen|first1=Madeleine J. H.|last2=Oliver|first2=James K.|last3=Putnam|first3=Hollie M.|last4=Gates|first4=Ruth D.|date=2015-02-24|title=Building coral reef resilience through assisted evolution|journal=Proceedings of the National Academy of Sciences|language=en|volume=112|issue=8|pages=2307–2313|doi=10.1073/pnas.1422301112|issn=0027-8424|pmid=25646461|pmc=4345611|bibcode=2015PNAS..112.2307V|doi-access=free}}</ref> These methods focus on altering the genetics of the zooxanthellae within coral rather than the alternative. | |||
{{Reflist|35em}} | |||
The first method is to induce acclimatization of the first generation of corals.<ref name="van Oppen-2015" /> The idea is that when adult and offspring corals are exposed to stressors, the zooxanthellae will gain a mutation. This method is based mostly on the chance that the zooxanthellae will acquire the specific trait that will allow it to better survive in warmer waters. The second method focuses on identifying what different kinds of zooxanthellae are within the coral and configuring how much of each zooxanthella lives within the coral at a given age.<ref name="van Oppen-2015" /> Use of zooxanthellae from the previous method would only boost success rates for this method. However, this method would only be applicable to younger corals, for now, because previous experiments of manipulation zooxanthellae communities at later life stages have all failed. The third method focuses on selective breeding tactics.<ref name="van Oppen-2015" /> Once selected, corals would be reared and exposed to simulated stressors in a laboratory. The last method is to genetically modify the zooxanthellae itself.<ref name="van Oppen-2015" /> When preferred mutations are acquired, the genetically modified zooxanthellae will be introduced to an aposymbiotic poly and a new coral will be produced. This method is the most laborious of the fourth, but researchers believe this method should be utilized more and holds the most promise in genetic engineering for coral restoration. | |||
===Invasive algae=== | |||
Hawaiian coral reefs smothered by the spread of invasive algae were managed with a two-prong approach: divers manually removed invasive algae, with the support of super-sucker barges. Grazing pressure on invasive algae needed to be increased to prevent the regrowth of the algae. Researchers found that native collector urchins were reasonable candidate grazers for algae biocontrol, to extirpate the remaining invasive algae from the reef.<ref name="Westbrook-2015" /> | |||
====Invasive algae in Caribbean reefs==== | |||
] | |||
Macroalgae, or better known as seaweed, has to potential to cause reef collapse because they can outcompete many coral species. Macroalgae can overgrow on corals, shade, block recruitment, release biochemicals that can hinder spawning, and potentially form bacteria harmful to corals.<ref>{{Cite journal|last1=Vieira|first1=Christophe|last2=Payri|first2=Claude|last3=Clerck|first3=Olivier|date=2016-09-08|title=A fresh look at macroalgal-coral interactions: are macroalgae a threat to corals? |journal=Perspectives in Phycology|volume=3|issue=3|pages=129–140|doi=10.1127/pip/2016/0068 |url=https://www.researchgate.net/publication/308886983}}</ref><ref name="Knowlton-2001">{{Cite journal |last=Knowlton|first=N.|date=2001-04-24|title=Sea urchin recovery from mass mortality: New hope for Caribbean coral reefs? |journal=Proceedings of the National Academy of Sciences|volume=98|issue=9 |pages=4822–4824 |doi=10.1073/pnas.091107198|pmid=11320228|pmc=33118|bibcode=2001PNAS...98.4822K |issn=0027-8424|doi-access=free}}</ref> Historically, algae growth was controlled by herbivorous fish and sea urchins. Parrotfish are a prime example of reef caretakers. Consequently, these two species can be considered as keystone species for reef environments because of their role in protecting reefs. | |||
Before the 1980s, Jamaica's reefs were thriving and well cared for, however, this all changed after ] occurred in 1980 and an unknown disease spread across the Caribbean. In the wake of these events, massive damage was caused to both the reefs and sea urchin population across Jamaican's reefs and into the Caribbean Sea. As little as 2% of the original sea urchin population survived the disease.<ref name="Knowlton-2001" /> Primary macroalgae succeeded the destroyed reefs and eventually larger, more resilient macroalgae soon took its place as the dominant organism.<ref name="Knowlton-2001" /><ref name="Edmunds-2001">{{Cite journal|last1=Edmunds|first1=P. J.|last2=Carpenter|first2=R. C.|date=2001-03-27|title=Recovery of Diadema antillarum reduces macroalgal cover and increases abundance of juvenile corals on a Caribbean reef|journal=Proceedings of the National Academy of Sciences|language=en|volume=98|issue=9|pages=5067–5071|doi=10.1073/pnas.071524598|pmid=11274358|pmc=33164|issn=0027-8424|doi-access=free}}</ref> Parrotfish and other herbivorous fish were few in numbers because of decades of overfishing and bycatch at the time.<ref name="Edmunds-2001" /> Historically, the Jamaican coast had 90% coral cover and was reduced to 5% in the 1990s.<ref name="Edmunds-2001" /> Eventually, corals were able to recover in areas where sea urchin populations were increasing. Sea urchins were able to feed and multiply and clear off substrates, leaving areas for coral polyps to anchor and mature. However, sea urchin populations are still not recovering as fast as researchers predicted, despite being highly fecundate.<ref name="Knowlton-2001" /> It is unknown whether or not the mysterious disease is still present and preventing sea urchin populations from rebounding. Regardless, these areas are slowly recovering with the aid of sea urchin grazing. This event supports an early restoration idea of cultivating and releasing sea urchins into reefs to prevent algal overgrowth.<ref>{{Cite journal|last1=McClanahan |first1=T.R.|last2=Kaunda-Arara|first2=B. |date=August 1996|title=Fishery Recovery in a Coral-reef Marine Park and Its Effect on the Adjacent Fishery|journal=Conservation Biology|volume=10|issue=4|pages=1187–1199 |doi=10.1046/j.1523-1739.1996.10041187.x|bibcode=1996ConBi..10.1187M |issn=0888-8892}}</ref><ref>{{Cite journal|last=Sammarco|first=Paul W.|date=1980 |title=Diadema and its relationship to coral spat mortality: Grazing, competition, and biological disturbance|journal=Journal of Experimental Marine Biology and Ecology|language=en|volume=45|issue=2 |pages=245–272|doi=10.1016/0022-0981(80)90061-1|bibcode=1980JEMBE..45..245S |issn=0022-0981}}</ref> | |||
===Microfragmentation and fusion=== | |||
In 2014, Christopher Page, Erinn Muller, and David Vaughan from the International Center for Coral Reef Research & Restoration at Mote Marine Laboratory in Summerland Key, Florida developed a new technology called "microfragmentation", in which they use a specialized diamond band saw to cut corals into 1 cm<sup>2</sup> fragments instead of 6 cm<sup>2</sup> to advance the growth of brain, boulder, and star corals.<ref name="Page-2018">{{Cite journal|last1=Page|first1=Christopher A.|last2=Muller|first2=Erinn M.|last3=Vaughan|first3=David E.|date=2018-11-01|title=Microfragmenting for the successful restoration of slow growing massive corals|journal=Ecological Engineering|language=en|volume=123|pages=86–94|doi=10.1016/j.ecoleng.2018.08.017|issn=0925-8574|doi-access=free|bibcode=2018EcEng.123...86P }}</ref> Corals ''Orbicella faveolata'' and ''Montastraea cavernosa'' were outplanted off the Florida's shores in several microfragment arrays. After two years, ''O. faveolata'' had grown 6.5x its original size while ''M. cavernosa'' had grown nearly twice its size.<ref name="Page-2018" /> Under conventional means, both corals would have required decades to reach the same size. It is suspected that if predation events had not occurred near the beginning of the experiment ''O. faveolata'' would have grown at least ten times its original size.<ref name="Page-2018" /> By using this method, ] successfully generated 25,000 corals within a single year, subsequently transplanting 10,000 of them into the Florida Keys. Shortly after, they discovered that these microfragments fused with other microfragments from the same parent coral. Typically, corals that are not from the same parent fight and kill nearby corals in an attempt to survive and expand. This new technology is known as "fusion" and has been shown to grow coral heads in just two years instead of the typical 25–75 years. After fusion occurs, the reef will act as a single organism rather than several independent reefs. Currently, there has been no published research into this method.<ref name="Page-2018" /> | |||
==See also== | |||
{{Portal|Ecology|Oceans}} | |||
* ] — Corals living in the cold waters of deeper, darker parts of the oceans | |||
* ] — Corals living in the mesopelagic or twilight zone | |||
* {{annotated link|Fossil Coral Reef}} | |||
* {{annotated link|Census of Coral Reefs}} | |||
* {{annotated link|Catlin Seaview Survey}} | |||
* {{annotated link|Coral reef organizations}} | |||
* {{annotated link|Sponge reef}} | |||
* {{annotated link|Pseudo-atoll}} | |||
==References== | ==References== | ||
{{ |
{{reflist}} | ||
* Butler, Steven. 1996. "Rod? Reel? Dynamite? A tough-love aid program takes aim at the devastation of the coral reefs". ''U.S. News and World Report'', 25 November 1996. | |||
==Further references== | |||
* Christie, P. 2005a. University of Washington, Lecture. 18 May 2005. | |||
* Christie, P. 2005b. University of Washington, Lecture. 4 May 2005. | |||
* {{cite journal | last1 = Clifton | first1 = Julian | year = 2003 | title = Prospects for Co-Management in Indonesia's Marine Protected Areas | journal = Marine Policy | volume = 27 | issue = 5| pages = 389–395 | doi = 10.1016/S0308-597X(03)00026-5}} | |||
* Courtney, Catherine and Alan White. 2000. ''Integrated Coastal Management in the Philippines''. Coastal Management; Taylor and Francis. | |||
* Fox, Helen. 2005. ''Experimental Assessment of Coral Reef Rehabilitation Following Blast Fishing''. The Nature Conservancy Coastal and Marine Indonesia Program. Blackwell Publishers Ltd, February 2005. | |||
* Gjertsen, Heidi. 2004. ''Can Habitat Protection Lead to Improvements in Human Well-Being? Evidence from Marine Protected Areas in the Philippines.'' | |||
* {{cite book|last1=Moyle |first1=PB |last2=Cech |first2=JJ |year=2003 |title=Fishes, An Introduction to Ichthyology |edition=5 |publisher=Benjamin Cummings |isbn=978-0-13-100847-2 |ref=harv}} | |||
* Sadovy, Y.J. ''Ecological Issues and the Trades in Live Reef Fishes, Part 1'' | |||
* . US EPA. | * . US EPA. | ||
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==External links== | ==External links== | ||
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{{Commons category|Coral reefs}} | {{Commons category|Coral reefs}} | ||
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* {{cite web|title = Coral Reef Factsheet|url = http://waittinstitute.org/coralreef/|access-date = June 8, 2015|publisher = Waitt Institute|archive-url = https://web.archive.org/web/20150609024654/http://waittinstitute.org/coralreef/|archive-date = June 9, 2015|url-status = dead}} | |||
*- At the Smithsonian Ocean Portal | |||
* | * overview at the Smithsonian Ocean Portal | ||
* {{Webarchive|url=https://web.archive.org/web/20131226001625/http://coral.aims.gov.au/info/about.jsp |date=26 December 2013 }} ''Australian Institute of Marine Science''. | |||
* | * | ||
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* | * {{Webarchive|url=https://web.archive.org/web/20120831082206/http://www.reefbase.org/ |date=31 August 2012 }} | ||
* Nova Southeastern University | * {{Webarchive|url=https://web.archive.org/web/20121023012451/http://www.nova.edu/ncri/ |date=October 23, 2012 }} Nova Southeastern University | ||
* | * {{Webarchive|url=https://web.archive.org/web/20130724124203/http://www.aquariumcouncil.org/ |date=24 July 2013 }} | ||
* University of Miami | * University of Miami | ||
* | *{{usurped|1=}} | ||
* {{Webarchive|url=https://web.archive.org/web/20110727042839/http://www.stanford.edu/group/microdocs/ |date=27 July 2011 }}: {{Webarchive|url=https://web.archive.org/web/20121024014723/http://www.stanford.edu/group/microdocs/typesofreefs.html |date=24 October 2012 }} & {{Webarchive|url=https://web.archive.org/web/20121024014829/http://www.stanford.edu/group/microdocs/reefstructure.html |date=24 October 2012 }} | |||
* | |||
* Active Florida environmental non-profit focusing on coral reef education and protection | |||
*: & | |||
* – Catlin Seaview Survey of reef, a database of images and other information | |||
*: Coral reef resources, images, education, threats, solutions | |||
*"" (archived). ], ''iBioSeminars'', 2011. | |||
* | |||
* | *". ], ''iBioSeminars'', 2011. | ||
* Living Reefs Foundation, Bermuda | |||
* {{cite web | |||
*'' by the ]. – {{YouTube|k9aWMIexrcs}}, featuring the report. | |||
|publisher=Science Daily | |||
|url=http://www.sciencedaily.com/releases/2009/06/090601111932.htm | |||
|date=June 3, 2009|title=In The Turf War Against Seaweed, Coral Reefs More Resilient Than Expected | |||
|accessdate=February, 2011}} | |||
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{{coastal geography}} | {{coastal geography}} | ||
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Latest revision as of 18:01, 21 December 2024
Outcrop of rock in the sea formed by the growth and deposit of stony coral skeletons
Marine habitats |
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Coastal habitats |
Ocean surface |
Open ocean |
Sea floor |
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
Coral belongs to the class Anthozoa in the animal phylum Cnidaria, which includes sea anemones and jellyfish. Unlike sea anemones, corals secrete hard carbonate exoskeletons that support and protect the coral. Most reefs grow best in warm, shallow, clear, sunny and agitated water. Coral reefs first appeared 485 million years ago, at the dawn of the Early Ordovician, displacing the microbial and sponge reefs of the Cambrian.
Sometimes called rainforests of the sea, shallow coral reefs form some of Earth's most diverse ecosystems. They occupy less than 0.1% of the world's ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, mollusks, worms, crustaceans, echinoderms, sponges, tunicates and other cnidarians. Coral reefs flourish in ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas.
Shallow tropical coral reefs have declined by 50% since 1950, partly because they are sensitive to water conditions. They are under threat from excess nutrients (nitrogen and phosphorus), rising ocean heat content and acidification, overfishing (e.g., from blast fishing, cyanide fishing, spearfishing on scuba), sunscreen use, and harmful land-use practices, including runoff and seeps (e.g., from injection wells and cesspools).
Coral reefs deliver ecosystem services for tourism, fisheries and shoreline protection. The annual global economic value of coral reefs has been estimated at anywhere from US$30–375 billion (1997 and 2003 estimates) to US$2.7 trillion (a 2020 estimate) to US$9.9 trillion (a 2014 estimate).
Though the shallow water tropical coral reefs are best known, there are also deeper water reef-forming corals, which live in colder water and in temperate seas.
Formation
Further information: Atoll, Fringing reef, and The Structure and Distribution of Coral ReefsMost coral reefs were formed after the Last Glacial Period when melting ice caused sea level to rise and flood continental shelves. Most coral reefs are less than 10,000 years old. As communities established themselves, the reefs grew upwards, pacing rising sea levels. Reefs that rose too slowly could become drowned, without sufficient light. Coral reefs are also found in the deep sea away from continental shelves, around oceanic islands and atolls. The majority of these islands are volcanic in origin. Others have tectonic origins where plate movements lifted the deep ocean floor.
In The Structure and Distribution of Coral Reefs, Charles Darwin set out his theory of the formation of atoll reefs, an idea he conceived during the voyage of the Beagle. He theorized that uplift and subsidence of Earth's crust under the oceans formed the atolls. Darwin set out a sequence of three stages in atoll formation. A fringing reef forms around an extinct volcanic island as the island and ocean floor subside. As the subsidence continues, the fringing reef becomes a barrier reef and ultimately an atoll reef.
- Darwin's theory starts with a volcanic island which becomes extinct
- As the island and ocean floor subside, coral growth builds a fringing reef, often including a shallow lagoon between the land and the main reef.
- As the subsidence continues, the fringing reef becomes a larger barrier reef further from the shore with a bigger and deeper lagoon inside.
- Ultimately, the island sinks below the sea, and the barrier reef becomes an atoll enclosing an open lagoon.
Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast to form fringing reefs, and can eventually grow to become a barrier reef.
Where the bottom is rising, fringing reefs can grow around the coast, but coral raised above sea level dies. If the land subsides slowly, the fringing reefs keep pace by growing upwards on a base of older, dead coral, forming a barrier reef enclosing a lagoon between the reef and the land. A barrier reef can encircle an island, and once the island sinks below sea level a roughly circular atoll of growing coral continues to keep up with the sea level, forming a central lagoon. Barrier reefs and atolls do not usually form complete circles but are broken in places by storms. Like sea level rise, a rapidly subsiding bottom can overwhelm coral growth, killing the coral and the reef, due to what is called coral drowning. Corals that rely on zooxanthellae can die when the water becomes too deep for their symbionts to adequately photosynthesize, due to decreased light exposure.
The two main variables determining the geomorphology, or shape, of coral reefs are the nature of the substrate on which they rest, and the history of the change in sea level relative to that substrate.
The approximately 20,000-year-old Great Barrier Reef offers an example of how coral reefs formed on continental shelves. Sea level was then 120 m (390 ft) lower than in the 21st century. As sea level rose, the water and the corals encroached on what had been hills of the Australian coastal plain. By 13,000 years ago, sea level had risen to 60 m (200 ft) lower than at present, and many hills of the coastal plains had become continental islands. As sea level rise continued, water topped most of the continental islands. The corals could then overgrow the hills, forming cays and reefs. Sea level on the Great Barrier Reef has not changed significantly in the last 6,000 years. The age of living reef structure is estimated to be between 6,000 and 8,000 years. Although the Great Barrier Reef formed along a continental shelf, and not around a volcanic island, Darwin's principles apply. Development stopped at the barrier reef stage, since Australia is not about to submerge. It formed the world's largest barrier reef, 300–1,000 m (980–3,280 ft) from shore, stretching for 2,000 km (1,200 mi).
Healthy tropical coral reefs grow horizontally from 1 to 3 cm (0.39 to 1.18 in) per year, and grow vertically anywhere from 1 to 25 cm (0.39 to 9.84 in) per year; however, they grow only at depths shallower than 150 m (490 ft) because of their need for sunlight, and cannot grow above sea level.
Material
As the name implies, coral reefs are made up of coral skeletons from mostly intact coral colonies. As other chemical elements present in corals become incorporated into the calcium carbonate deposits, aragonite is formed. However, shell fragments and the remains of coralline algae such as the green-segmented genus Halimeda can add to the reef's ability to withstand damage from storms and other threats. Such mixtures are visible in structures such as Eniwetok Atoll.
In the geologic past
The times of maximum reef development were in the Middle Cambrian (513–501 Ma), Devonian (416–359 Ma) and Carboniferous (359–299 Ma), owing to extinct order Rugosa corals, and Late Cretaceous (100–66 Ma) and Neogene (23 Ma–present), owing to order Scleractinia corals.
Not all reefs in the past were formed by corals: those in the Early Cambrian (542–513 Ma) resulted from calcareous algae and archaeocyathids (small animals with conical shape, probably related to sponges) and in the Late Cretaceous (100–66 Ma), when reefs formed by a group of bivalves called rudists existed; one of the valves formed the main conical structure and the other, much smaller valve acted as a cap.
Measurements of the oxygen isotopic composition of the aragonitic skeleton of coral reefs, such as Porites, can indicate changes in sea surface temperature and sea surface salinity conditions during the growth of the coral. This technique is often used by climate scientists to infer a region's paleoclimate.
Types
Since Darwin's identification of the three classical reef formations – the fringing reef around a volcanic island becoming a barrier reef and then an atoll – scientists have identified further reef types. While some sources find only three, Thomas lists "Four major forms of large-scale coral reefs" – the fringing reef, barrier reef, atoll and table reef based on Stoddart, D.R. (1969). Spalding et al. list four main reef types that can be clearly illustrated – the fringing reef, barrier reef, atoll, and "bank or platform reef"—and notes that many other structures exist which do not conform easily to strict definitions, including the "patch reef".
Fringing reef
Main article: Fringing reefA fringing reef, also called a shore reef, is directly attached to a shore, or borders it with an intervening narrow, shallow channel or lagoon. It is the most common reef type. Fringing reefs follow coastlines and can extend for many kilometres. They are usually less than 100 metres wide, but some are hundreds of metres wide. Fringing reefs are initially formed on the shore at the low water level and expand seawards as they grow in size. The final width depends on where the sea bed begins to drop steeply. The surface of the fringe reef generally remains at the same height: just below the waterline. In older fringing reefs, whose outer regions pushed far out into the sea, the inner part is deepened by erosion and eventually forms a lagoon. Fringing reef lagoons can become over 100 metres wide and several metres deep. Like the fringing reef itself, they run parallel to the coast. The fringing reefs of the Red Sea are "some of the best developed in the world" and occur along all its shores except off sandy bays.
Barrier reef
Barrier reefs are separated from a mainland or island shore by a deep channel or lagoon. They resemble the later stages of a fringing reef with its lagoon but differ from the latter mainly in size and origin. Their lagoons can be several kilometres wide and 30 to 70 metres deep. Above all, the offshore outer reef edge formed in open water rather than next to a shoreline. Like an atoll, it is thought that these reefs are formed either as the seabed lowered or sea level rose. Formation takes considerably longer than for a fringing reef, thus barrier reefs are much rarer.
The best known and largest example of a barrier reef is the Australian Great Barrier Reef. Other major examples are the Mesoamerican Barrier Reef System and the New Caledonian Barrier Reef. Barrier reefs are also found on the coasts of Providencia, Mayotte, the Gambier Islands, on the southeast coast of Kalimantan, on parts of the coast of Sulawesi, southeastern New Guinea and the south coast of the Louisiade Archipelago.
Platform reef
Platform reefs, variously called bank or table reefs, can form on the continental shelf, as well as in the open ocean, in fact anywhere where the seabed rises close enough to the surface of the ocean to enable the growth of zooxanthemic, reef-forming corals. Platform reefs are found in the southern Great Barrier Reef, the Swain and Capricorn Group on the continental shelf, about 100–200 km from the coast. Some platform reefs of the northern Mascarenes are several thousand kilometres from the mainland. Unlike fringing and barrier reefs which extend only seaward, platform reefs grow in all directions. They are variable in size, ranging from a few hundred metres to many kilometres across. Their usual shape is oval to elongated. Parts of these reefs can reach the surface and form sandbanks and small islands around which may form fringing reefs. A lagoon may form In the middle of a platform reef.
Platform reefs are typically situated within atolls, where they adopt the name "patch reefs" and often span a diameter of just a few dozen meters. In instances where platform reefs develop along elongated structures, such as old and weathered barrier reefs, they tend to arrange themselves in a linear formation. This is the case, for example, on the east coast of the Red Sea near Jeddah. In old platform reefs, the inner part can be so heavily eroded that it forms a pseudo-atoll. These can be distinguished from real atolls only by detailed investigation, possibly including core drilling. Some platform reefs of the Laccadives are U-shaped, due to wind and water flow.
Atoll
Main article: AtollAtolls or atoll reefs are a more or less circular or continuous barrier reef that extends all the way around a lagoon without a central island. They are usually formed from fringing reefs around volcanic islands. Over time, the island erodes away and sinks below sea level. Atolls may also be formed by the sinking of the seabed or rising of the sea level. A ring of reefs results, which enclose a lagoon. Atolls are numerous in the South Pacific, where they usually occur in mid-ocean, for example, in the Caroline Islands, the Cook Islands, French Polynesia, the Marshall Islands and Micronesia.
Atolls are found in the Indian Ocean, for example, in the Maldives, the Chagos Islands, the Seychelles and around Cocos Island. The entire Maldives consist of 26 atolls.
Other reef types or variants
- Apron reef – short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore. The initial stage of a fringing reef.
- Bank reef – isolated, flat-topped reef larger than a patch reef and usually on mid-shelf regions and linear or semi-circular in shape; a type of platform reef.
- Patch reef – common, isolated, comparatively small reef outcrop, usually within a lagoon or embayment, often circular and surrounded by sand or seagrass. Can be considered as a type of platform reef or as features of fringing reefs, atolls and barrier reefs. The patches may be surrounded by a ring of reduced seagrass cover referred to as a grazing halo.
- Ribbon reef – long, narrow, possibly winding reef, usually associated with an atoll lagoon. Also called a shelf-edge reef or sill reef.
- Drying reef – a part of a reef which is above water at low tide but submerged at high tide
- Habili – reef specific to the Red Sea; does not reach near enough to the surface to cause visible surf; may be a hazard to ships (from the Arabic for "unborn")
- Microatoll – community of species of corals; vertical growth limited by average tidal height; growth morphologies offer a low-resolution record of patterns of sea level change; fossilized remains can be dated using radioactive carbon dating and have been used to reconstruct Holocene sea levels
- Cays – small, low-elevation, sandy islands formed on the surface of coral reefs from eroded material that piles up, forming an area above sea level; can be stabilized by plants to become habitable; occur in tropical environments throughout the Pacific, Atlantic and Indian Oceans (including the Caribbean and on the Great Barrier Reef and Belize Barrier Reef), where they provide habitable and agricultural land
- Seamount or guyot – formed when a coral reef on a volcanic island subsides; tops of seamounts are rounded and guyots are flat; flat tops of guyots, or tablemounts, are due to erosion by waves, winds, and atmospheric processes
Zones
Coral reef ecosystems contain distinct zones that host different kinds of habitats. Usually, three major zones are recognized: the fore reef, reef crest, and the back reef (frequently referred to as the reef lagoon).
The three zones are physically and ecologically interconnected. Reef life and oceanic processes create opportunities for the exchange of seawater, sediments, nutrients and marine life.
Most coral reefs exist in waters less than 50 m deep. Some inhabit tropical continental shelves where cool, nutrient-rich upwelling does not occur, such as the Great Barrier Reef. Others are found in the deep ocean surrounding islands or as atolls, such as in the Maldives. The reefs surrounding islands form when islands subside into the ocean, and atolls form when an island subsides below the surface of the sea.
Alternatively, Moyle and Cech distinguish six zones, though most reefs possess only some of the zones.
The reef surface is the shallowest part of the reef. It is subject to surge and tides. When waves pass over shallow areas, they shoal, as shown in the adjacent diagram. This means the water is often agitated. These are the precise condition under which corals flourish. The light is sufficient for photosynthesis by the symbiotic zooxanthellae, and agitated water brings plankton to feed the coral.
The off-reef floor is the shallow sea floor surrounding a reef. This zone occurs next to reefs on continental shelves. Reefs around tropical islands and atolls drop abruptly to great depths and do not have such a floor. Usually sandy, the floor often supports seagrass meadows which are important foraging areas for reef fish.
The reef drop-off is, for its first 50 m, habitat for reef fish who find shelter on the cliff face and plankton in the water nearby. The drop-off zone applies mainly to the reefs surrounding oceanic islands and atolls.
The reef face is the zone above the reef floor or the reef drop-off. This zone is often the reef's most diverse area. Coral and calcareous algae provide complex habitats and areas that offer protection, such as cracks and crevices. Invertebrates and epiphytic algae provide much of the food for other organisms. A common feature on this forereef zone is spur and groove formations that serve to transport sediment downslope.
The reef flat is the sandy-bottomed flat, which can be behind the main reef, containing chunks of coral. This zone may border a lagoon and serve as a protective area, or it may lie between the reef and the shore, and in this case is a flat, rocky area. Fish tend to prefer it when it is present.
The reef lagoon is an entirely enclosed region, which creates an area less affected by wave action and often contains small reef patches.
However, the topography of coral reefs is constantly changing. Each reef is made up of irregular patches of algae, sessile invertebrates, and bare rock and sand. The size, shape and relative abundance of these patches change from year to year in response to the various factors that favor one type of patch over another. Growing coral, for example, produces constant change in the fine structure of reefs. On a larger scale, tropical storms may knock out large sections of reef and cause boulders on sandy areas to move.
Locations
See also: List of reefs
Coral reefs are estimated to cover 284,300 km (109,800 sq mi), just under 0.1% of the oceans' surface area. The Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs account for 7.6%.
Although corals exist both in temperate and tropical waters, shallow-water reefs form only in a zone extending from approximately 30° N to 30° S of the equator. Tropical corals do not grow at depths of over 50 meters (160 ft). The optimum temperature for most coral reefs is 26–27 °C (79–81 °F), and few reefs exist in waters below 18 °C (64 °F). When the net production by reef building corals no longer keeps pace with relative sea level and the reef structure permanently drowns a Darwin Point is reached. One such point exists at the northwestern end of the Hawaiian Archipelago; see Evolution of Hawaiian volcanoes#Coral atoll stage.
However, reefs in the Persian Gulf have adapted to temperatures of 13 °C (55 °F) in winter and 38 °C (100 °F) in summer. 37 species of scleractinian corals inhabit such an environment around Larak Island.
Deep-water coral inhabits greater depths and colder temperatures at much higher latitudes, as far north as Norway. Although deep water corals can form reefs, little is known about them.
The northernmost coral reef on Earth is located near Eilat, Israel. Coral reefs are rare along the west coasts of the Americas and Africa, due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas (the Humboldt, Benguela, and Canary Currents, respectively). Corals are seldom found along the coastline of South Asia—from the eastern tip of India (Chennai) to the Bangladesh and Myanmar borders—as well as along the coasts of northeastern South America and Bangladesh, due to the freshwater release from the Amazon and Ganges Rivers respectively.
Significant coral reefs include:
- The Great Barrier Reef—largest, comprising over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometers (1,600 mi) off Queensland, Australia
- The Mesoamerican Barrier Reef System—second largest, stretching 1,000 kilometers (620 mi) from Isla Contoy at the tip of the Yucatán Peninsula down to the Bay Islands of Honduras
- The New Caledonia Barrier Reef—second longest double barrier reef, covering 1,500 kilometers (930 mi)
- The Andros, Bahamas Barrier Reef—third largest, following the east coast of Andros Island, Bahamas, between Andros and Nassau
- The Red Sea—includes 6,000-year-old fringing reefs located along a 2,000 km (1,240 mi) coastline
- The Florida Reef Tract—largest continental US reef and the third-largest coral barrier reef, extends from Soldier Key, located in Biscayne Bay, to the Dry Tortugas in the Gulf of Mexico
- Blake Plateau has the world's largest known deep-water coral reef, comprising a 6.4 million acre reef that stretches from Miami to Charleston, S. C. Its discovery was announced in January 2024.
- Pulley Ridge—deepest photosynthetic coral reef, Florida
- Numerous reefs around the Maldives
- The Philippines coral reef area, the second-largest in Southeast Asia, is estimated at 26,000 square kilometres. 915 reef fish species and more than 400 scleractinian coral species, 12 of which are endemic are found there.
- The Raja Ampat Islands in Indonesia's Southwest Papua province offer the highest known marine diversity.
- Bermuda is known for its northernmost coral reef system, located at 32°24′N 64°48′W / 32.4°N 64.8°W / 32.4; -64.8. The presence of coral reefs at this high latitude is due to the proximity of the Gulf Stream. Bermuda coral species represent a subset of those found in the greater Caribbean.
- The world's northernmost individual coral reef is located in the Finlayson Channel, in the inside passage of British Columbia, Canada.
- The world's southernmost coral reef is at Lord Howe Island, in the Pacific Ocean off the east coast of Australia.
Coral
Main article: CoralWhen alive, corals are colonies of small animals embedded in calcium carbonate shells. Coral heads consist of accumulations of individual animals called polyps, arranged in diverse shapes. Polyps are usually tiny, but they can range in size from a pinhead to 12 inches (30 cm) across.
Reef-building or hermatypic corals live only in the photic zone (above 70 m), the depth to which sufficient sunlight penetrates the water.
Zooxanthellae
Coral polyps do not photosynthesize, but have a symbiotic relationship with microscopic algae (dinoflagellates) of the genus Symbiodinium, commonly referred to as zooxanthellae. These organisms live within the polyps' tissues and provide organic nutrients that nourish the polyp in the form of glucose, glycerol and amino acids. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Without their symbionts, coral growth would be too slow to form significant reef structures. Corals get up to 90% of their nutrients from their symbionts. In return, as an example of mutualism, the corals shelter the zooxanthellae, averaging one million for every cubic centimetre of coral, and provide a constant supply of the carbon dioxide they need for photosynthesis.
The varying pigments in different species of zooxanthellae give them an overall brown or golden-brown appearance and give brown corals their colors. Other pigments such as reds, blues, greens, etc. come from colored proteins made by the coral animals. Coral that loses a large fraction of its zooxanthellae becomes white (or sometimes pastel shades in corals that are pigmented with their own proteins) and is said to be bleached, a condition which, unless corrected, can kill the coral.
There are eight clades of Symbiodinium phylotypes. Most research has been conducted on clades A–D. Each clade contributes their own benefits as well as less compatible attributes to the survival of their coral hosts. Each photosynthetic organism has a specific level of sensitivity to photodamage to compounds needed for survival, such as proteins. Rates of regeneration and replication determine the organism's ability to survive. Phylotype A is found more in the shallow waters. It is able to produce mycosporine-like amino acids that are UV resistant, using a derivative of glycerin to absorb the UV radiation and allowing them to better adapt to warmer water temperatures. In the event of UV or thermal damage, if and when repair occurs, it will increase the likelihood of survival of the host and symbiont. This leads to the idea that, evolutionarily, clade A is more UV resistant and thermally resistant than the other clades.
Clades B and C are found more frequently in deeper water, which may explain their higher vulnerability to increased temperatures. Terrestrial plants that receive less sunlight because they are found in the undergrowth are analogous to clades B, C, and D. Since clades B through D are found at deeper depths, they require an elevated light absorption rate to be able to synthesize as much energy. With elevated absorption rates at UV wavelengths, these phylotypes are more prone to coral bleaching versus the shallow clade A.
Clade D has been observed to be high temperature-tolerant, and has a higher rate of survival than clades B and C during modern bleaching events.
Skeleton
Reefs grow as polyps and other organisms deposit calcium carbonate, the basis of coral, as a skeletal structure beneath and around themselves, pushing the coral head's top upwards and outwards. Waves, grazing fish (such as parrotfish), sea urchins, sponges and other forces and organisms act as bioeroders, breaking down coral skeletons into fragments that settle into spaces in the reef structure or form sandy bottoms in associated reef lagoons.
Typical shapes for coral species are named by their resemblance to terrestrial objects such as wrinkled brains, cabbages, table tops, antlers, wire strands and pillars. These shapes can depend on the life history of the coral, like light exposure and wave action, and events such as breakages.
Reproduction
External videos | |
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" Out of Tune – Breakdown of Coral Spawning Synchrony", Tom Shlesinger, Sep 5, 2019. |
Corals reproduce both sexually and asexually. An individual polyp uses both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. The reproductive cells are found on the mesenteries, membranes that radiate inward from the layer of tissue that lines the stomach cavity. Some mature adult corals are hermaphroditic; others are exclusively male or female. A few species change sex as they grow.
Internally fertilized eggs develop in the polyp for a period ranging from days to weeks. Subsequent development produces a tiny larva, known as a planula. Externally fertilized eggs develop during synchronized spawning. Polyps across a reef simultaneously release eggs and sperm into the water en masse. Spawn disperse over a large area. The timing of spawning depends on time of year, water temperature, and tidal and lunar cycles. Spawning is most successful given little variation between high and low tide. The less water movement, the better the chance for fertilization. The release of eggs or planula usually occurs at night and is sometimes in phase with the lunar cycle (three to six days after a full moon).
The period from release to settlement lasts only a few days, but some planulae can survive afloat for several weeks. During this process, the larvae may use several different cues to find a suitable location for settlement. At long distances sounds from existing reefs are likely important, while at short distances chemical compounds become important. The larvae are vulnerable to predation and environmental conditions. The lucky few planulae that successfully attach to substrate then compete for food and space.
Gallery of reef-building corals
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Other reef builders
Corals are the most prodigious reef-builders. However many other organisms living in the reef community contribute skeletal calcium carbonate in the same manner as corals. These include coralline algae, some sponges and bivalves. Reefs are always built by the combined efforts of these different phyla, with different organisms leading reef-building in different geological periods.
Coralline algae
Main article: Coralline algae See also: Coralline rockCoralline algae are important contributors to reef structure. Although their mineral deposition rates are much slower than corals, they are more tolerant of rough wave-action, and so help to create a protective crust over those parts of the reef subjected to the greatest forces by waves, such as the reef front facing the open ocean. They also strengthen the reef structure by depositing limestone in sheets over the reef surface.
Sponges
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"Sclerosponge" is the descriptive name for all Porifera that build reefs. In the early Cambrian period, Archaeocyatha sponges were the world's first reef-building organisms, and sponges were the only reef-builders until the Ordovician. Sclerosponges still assist corals building modern reefs, but like coralline algae are much slower-growing than corals and their contribution is (usually) minor.
In the northern Pacific Ocean cloud sponges still create deep-water mineral-structures without corals, although the structures are not recognizable from the surface like tropical reefs. They are the only extant organisms known to build reef-like structures in cold water.
Bivalves
See also: Bivalve reefOyster reefs are dense aggregations of oysters living in colonial communities. Other regionally-specific names for these structures include oyster beds and oyster banks. Oyster larvae require a hard substrate or surface to attach on, which includes the shells of old or dead oysters. Thus reefs can build up over time as new larvae settle on older individuals. Crassostrea virginica were once abundant in Chesapeake Bay and shorelines bordering the Atlantic coastal plain until the late nineteenth century. Ostrea angasi is a species of flat oyster that had also formed large reefs in South Australia.
Hippuritida, an extinct order of bivalves known as rudists, were major reef-building organisms during the Cretaceous. By the mid-Cretaceous, rudists became the dominant tropical reef-builders, becoming more numerous than scleractinian corals. During this period, ocean temperatures and saline levels—which corals are sensitive to—were higher than it is today, which may have contributed to the success of rudist reefs.
Gastropods
Some gastropods, like family Vermetidae, are sessile and cement themselves to the substrate, contributing to the reef building.
Darwin's paradox
Darwin's paradox"Coral... seems to proliferate when ocean waters are warm, poor, clear and agitated, a fact which Darwin had already noted when he passed through Tahiti in 1842. This constitutes a fundamental paradox, shown quantitatively by the apparent impossibility of balancing input and output of the nutritive elements which control the coral polyp metabolism.
Recent oceanographic research has brought to light the reality of this paradox by confirming that the oligotrophy of the ocean euphotic zone persists right up to the swell-battered reef crest. When you approach the reef edges and atolls from the quasidesert of the open sea, the near absence of living matter suddenly becomes a plethora of life, without transition. So why is there something rather than nothing, and more precisely, where do the necessary nutrients for the functioning of this extraordinary coral reef machine come from?" — Francis Rougerie
In The Structure and Distribution of Coral Reefs, published in 1842, Darwin described how coral reefs were found in some tropical areas but not others, with no obvious cause. The largest and strongest corals grew in parts of the reef exposed to the most violent surf and corals were weakened or absent where loose sediment accumulated.
Tropical waters contain few nutrients yet a coral reef can flourish like an "oasis in the desert". This has given rise to the ecosystem conundrum, sometimes called "Darwin's paradox": "How can such high production flourish in such nutrient poor conditions?"
Coral reefs support over one-quarter of all marine species. This diversity results in complex food webs, with large predator fish eating smaller forage fish that eat yet smaller zooplankton and so on. However, all food webs eventually depend on plants, which are the primary producers. Coral reefs typically produce 5–10 grams of carbon per square meter per day (gC·m·day) biomass.
One reason for the unusual clarity of tropical waters is their nutrient deficiency and drifting plankton. Further, the sun shines year-round in the tropics, warming the surface layer, making it less dense than subsurface layers. The warmer water is separated from deeper, cooler water by a stable thermocline, where the temperature makes a rapid change. This keeps the warm surface waters floating above the cooler deeper waters. In most parts of the ocean, there is little exchange between these layers. Organisms that die in aquatic environments generally sink to the bottom, where they decompose, which releases nutrients in the form of nitrogen (N), phosphorus (P) and potassium (K). These nutrients are necessary for plant growth, but in the tropics, they do not directly return to the surface.
Plants form the base of the food chain and need sunlight and nutrients to grow. In the ocean, these plants are mainly microscopic phytoplankton which drift in the water column. They need sunlight for photosynthesis, which powers carbon fixation, so they are found only relatively near the surface, but they also need nutrients. Phytoplankton rapidly use nutrients in the surface waters, and in the tropics, these nutrients are not usually replaced because of the thermocline.
Explanations
Around coral reefs, lagoons fill in with material eroded from the reef and the island. They become havens for marine life, providing protection from waves and storms.
Most importantly, reefs recycle nutrients, which happens much less in the open ocean. In coral reefs and lagoons, producers include phytoplankton, as well as seaweed and coralline algae, especially small types called turf algae, which pass nutrients to corals. The phytoplankton form the base of the food chain and are eaten by fish and crustaceans. Recycling reduces the nutrient inputs needed overall to support the community.
Corals also absorb nutrients, including inorganic nitrogen and phosphorus, directly from water. Many corals extend their tentacles at night to catch zooplankton that pass near. Zooplankton provide the polyp with nitrogen, and the polyp shares some of the nitrogen with the zooxanthellae, which also require this element.
Sponges live in crevices in the reefs. They are efficient filter feeders, and in the Red Sea they consume about 60% of the phytoplankton that drifts by. Sponges eventually excrete nutrients in a form that corals can use.
The roughness of coral surfaces is key to coral survival in agitated waters. Normally, a boundary layer of still water surrounds a submerged object, which acts as a barrier. Waves breaking on the extremely rough edges of corals disrupt the boundary layer, allowing the corals access to passing nutrients. Turbulent water thereby promotes reef growth. Without the access to nutrients brought by rough coral surfaces, even the most effective recycling would not suffice.
Deep nutrient-rich water entering coral reefs through isolated events may have significant effects on temperature and nutrient systems. This water movement disrupts the relatively stable thermocline that usually exists between warm shallow water and deeper colder water. Temperature regimes on coral reefs in the Bahamas and Florida are highly variable with temporal scales of minutes to seasons and spatial scales across depths.
Water can pass through coral reefs in various ways, including current rings, surface waves, internal waves and tidal changes. Movement is generally created by tides and wind. As tides interact with varying bathymetry and wind mixes with surface water, internal waves are created. An internal wave is a gravity wave that moves along density stratification within the ocean. When a water parcel encounters a different density it oscillates and creates internal waves. While internal waves generally have a lower frequency than surface waves, they often form as a single wave that breaks into multiple waves as it hits a slope and moves upward. This vertical breakup of internal waves causes significant diapycnal mixing and turbulence. Internal waves can act as nutrient pumps, bringing plankton and cool nutrient-rich water to the surface.
The irregular structure characteristic of coral reef bathymetry may enhance mixing and produce pockets of cooler water and variable nutrient content. Arrival of cool, nutrient-rich water from depths due to internal waves and tidal bores has been linked to growth rates of suspension feeders and benthic algae as well as plankton and larval organisms. The seaweed Codium isthmocladum reacts to deep water nutrient sources because their tissues have different concentrations of nutrients dependent upon depth. Aggregations of eggs, larval organisms and plankton on reefs respond to deep water intrusions. Similarly, as internal waves and bores move vertically, surface-dwelling larval organisms are carried toward the shore. This has significant biological importance to cascading effects of food chains in coral reef ecosystems and may provide yet another key to unlocking the paradox.
Cyanobacteria provide soluble nitrates via nitrogen fixation.
Coral reefs often depend on surrounding habitats, such as seagrass meadows and mangrove forests, for nutrients. Seagrass and mangroves supply dead plants and animals that are rich in nitrogen and serve to feed fish and animals from the reef by supplying wood and vegetation. Reefs, in turn, protect mangroves and seagrass from waves and produce sediment in which the mangroves and seagrass can root.
Biodiversity
Tube sponges attracting cardinal fishes, glassfishes and wrassesOver 4,000 species of fish inhabit coral reefs.Organisms can cover every square inch of a coral reef.Coral reefs form some of the world's most productive ecosystems, providing complex and varied marine habitats that support a wide range of organisms. Fringing reefs just below low tide level have a mutually beneficial relationship with mangrove forests at high tide level and sea grass meadows in between: the reefs protect the mangroves and seagrass from strong currents and waves that would damage them or erode the sediments in which they are rooted, while the mangroves and sea grass protect the coral from large influxes of silt, fresh water and pollutants. This level of variety in the environment benefits many coral reef animals, which, for example, may feed in the sea grass and use the reefs for protection or breeding.
Reefs are home to a variety of animals, including fish, seabirds, sponges, cnidarians (which includes some types of corals and jellyfish), worms, crustaceans (including shrimp, cleaner shrimp, spiny lobsters and crabs), mollusks (including cephalopods), echinoderms (including starfish, sea urchins and sea cucumbers), sea squirts, sea turtles and sea snakes. Aside from humans, mammals are rare on coral reefs, with visiting cetaceans such as dolphins the main exception. A few species feed directly on corals, while others graze on algae on the reef. Reef biomass is positively related to species diversity.
The same hideouts in a reef may be regularly inhabited by different species at different times of day. Nighttime predators such as cardinalfish and squirrelfish hide during the day, while damselfish, surgeonfish, triggerfish, wrasses and parrotfish hide from eels and sharks.
The great number and diversity of hiding places in coral reefs, i.e. refuges, are the most important factor causing the great diversity and high biomass of the organisms in coral reefs.
Coral reefs also have a very high degree of microorganism diversity compared to other environments.
Algae
Reefs are chronically at risk of algal encroachment. Overfishing and excess nutrient supply from onshore can enable algae to outcompete and kill the coral. Increased nutrient levels can be a result of sewage or chemical fertilizer runoff. Runoff can carry nitrogen and phosphorus which promote excess algae growth. Algae can sometimes out-compete the coral for space. The algae can then smother the coral by decreasing the oxygen supply available to the reef. Decreased oxygen levels can slow down calcification rates, weakening the coral and leaving it more susceptible to disease and degradation. Algae inhabit a large percentage of surveyed coral locations. The algal population consists of turf algae, coralline algae and macro algae. Some sea urchins (such as Diadema antillarum) eat these algae and could thus decrease the risk of algal encroachment.
Sponges
Sponges are essential for the functioning of the coral reef system. Algae and corals in coral reefs produce organic material. This is filtered through sponges which convert this organic material into small particles which in turn are absorbed by algae and corals. Sponges are essential to the coral reef system however, they are quite different from corals. While corals are complex and many celled while sponges are very simple organisms with no tissue. They are alike in that they are both immobile aquatic invertebrates but otherwise are completely different.
Types of sponges-
There are several different species of sea sponge. They come in multiple shapes and sizes and all have unique characteristics. Some types of sea sponges include; the tube sponge, vase sponge, yellow sponge, bright red tree sponge, painted tunicate sponge, and the sea squirt sponge.
Medicinal Qualities of Sea Sponges-
Sea sponges have provided the base for many life saving medications. Scientists began to study them in the 1940s and after a few years, discovered that sea sponges contain properties that can stop viral infections. The first drug developed from sea sponges was released in 1969.
Fish
Main article: Coral reef fishOver 4,000 species of fish inhabit coral reefs. The reasons for this diversity remain unclear. Hypotheses include the "lottery", in which the first (lucky winner) recruit to a territory is typically able to defend it against latecomers, "competition", in which adults compete for territory, and less-competitive species must be able to survive in poorer habitat, and "predation", in which population size is a function of postsettlement piscivore mortality. Healthy reefs can produce up to 35 tons of fish per square kilometre each year, but damaged reefs produce much less.
Invertebrates
Sea urchins, Dotidae and sea slugs eat seaweed. Some species of sea urchins, such as Diadema antillarum, can play a pivotal part in preventing algae from overrunning reefs. Researchers are investigating the use of native collector urchins, Tripneustes gratilla, for their potential as biocontrol agents to mitigate the spread of invasive algae species on coral reefs. Nudibranchia and sea anemones eat sponges.
A number of invertebrates, collectively called "cryptofauna", inhabit the coral skeletal substrate itself, either boring into the skeletons (through the process of bioerosion) or living in pre-existing voids and crevices. Animals boring into the rock include sponges, bivalve mollusks, and sipunculans. Those settling on the reef include many other species, particularly crustaceans and polychaete worms.
Seabirds
Coral reef systems provide important habitats for seabird species, some endangered. For example, Midway Atoll in Hawaii supports nearly three million seabirds, including two-thirds (1.5 million) of the global population of Laysan albatross, and one-third of the global population of black-footed albatross. Each seabird species has specific sites on the atoll where they nest. Altogether, 17 species of seabirds live on Midway. The short-tailed albatross is the rarest, with fewer than 2,200 surviving after excessive feather hunting in the late 19th century.
Other
Sea snakes feed exclusively on fish and their eggs. Marine birds, such as herons, gannets, pelicans and boobies, feed on reef fish. Some land-based reptiles intermittently associate with reefs, such as monitor lizards, the marine crocodile and semiaquatic snakes, such as Laticauda colubrina. Sea turtles, particularly hawksbill sea turtles, feed on sponges.
- Schooling reef fish
- Caribbean reef squid
- Banded coral shrimp
- Whitetip reef shark
- Green turtle
- Giant clam
- Soft coral, cup coral, sponges and ascidians
- Banded sea krait
- The shell of Latiaxis wormaldi, a coral snail
Ecosystem services
Coral reefs deliver ecosystem services to tourism, fisheries and coastline protection. The global economic value of coral reefs has been estimated to be between US$29.8 billion and $375 billion per year. About 500 million people benefit from ecosystem services provided by coral reefs.
The economic cost over a 25-year period of destroying one square kilometre of coral reef has been estimated to be somewhere between $137,000 and $1,200,000.
To improve the management of coastal coral reefs, the World Resources Institute (WRI) developed and published tools for calculating the value of coral reef-related tourism, shoreline protection and fisheries, partnering with five Caribbean countries. As of April 2011, published working papers covered St. Lucia, Tobago, Belize, and the Dominican Republic. The WRI was "making sure that the study results support improved coastal policies and management planning". The Belize study estimated the value of reef and mangrove services at $395–559 million annually.
Bermuda's coral reefs provide economic benefits to the Island worth on average $722 million per year, based on six key ecosystem services, according to Sarkis et al (2010).
Shoreline protection
Coral reefs protect shorelines by absorbing wave energy, and many small islands would not exist without reefs. Coral reefs can reduce wave energy by 97%, helping to prevent loss of life and property damage. Coastlines protected by coral reefs are also more stable in terms of erosion than those without. Reefs can attenuate waves as well as or better than artificial structures designed for coastal defence such as breakwaters. An estimated 197 million people who live both below 10 m elevation and within 50 km of a reef consequently may receive risk reduction benefits from reefs. Restoring reefs is significantly cheaper than building artificial breakwaters in tropical environments. Expected damages from flooding would double, and costs from frequent storms would triple without the topmost meter of reefs. For 100-year storm events, flood damages would increase by 91% to $US 272 billion without the top meter.
Fisheries
About six million tons of fish are taken each year from coral reefs. Well-managed reefs have an average annual yield of 15 tons of seafood per square kilometre. Southeast Asia's coral reef fisheries alone yield about $2.4 billion annually from seafood.
Threats
See also: Environmental issues with coral reefs, Coral bleaching, and Environmental threats to the Great Barrier ReefExternal videos | |
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Chasing Coral – inventing the first time-lapse camera to record bleaching events as they happen (Netflix, full episode) |
Since their emergence 485 million years ago, coral reefs have faced many threats, including disease, predation, invasive species, bioerosion by grazing fish, algal blooms, and geologic hazards. Recent human activities present new threats. From 2009 to 2018, coral reefs worldwide declined 14%.
Human activities that threaten coral include coral mining, bottom trawling, and the digging of canals and accesses into islands and bays, all of which can damage marine ecosystems if not done sustainably. Other localized threats include blast fishing, overfishing, coral overmining, and marine pollution, including use of the banned anti-fouling biocide tributyltin; although absent in developed countries, these activities continue in places with few environmental protections or poor regulatory enforcement. Chemicals in sunscreens may awaken latent viral infections in zooxanthellae and impact reproduction. However, concentrating tourism activities via offshore platforms has been shown to limit the spread of coral disease by tourists.
Greenhouse gas emissions present a broader threat through sea temperature rise and sea level rise, resulting in widespread coral bleaching and loss of coral cover. Climate change causes more frequent and more severe storms, also changes ocean circulation patterns, which can destroy coral reefs.Ocean acidification also affects corals by decreasing calcification rates and increasing dissolution rates, although corals can adapt their calcifying fluids to changes in seawater pH and carbonate levels to mitigate the impact. Volcanic and human-made aerosol pollution can modulate regional sea surface temperatures.
In 2011, two researchers suggested that "extant marine invertebrates face the same synergistic effects of multiple stressors" that occurred during the end-Permian extinction, and that genera "with poorly buffered respiratory physiology and calcareous shells", such as corals, were particularly vulnerable.
Corals respond to stress by "bleaching", or expelling their colorful zooxanthellate endosymbionts. Corals with Clade C zooxanthellae are generally vulnerable to heat-induced bleaching, whereas corals with the hardier Clade A or D are generally resistant, as are tougher coral genera like Porites and Montipora.
Every 4–7 years, an El Niño event causes some reefs with heat-sensitive corals to bleach, with especially widespread bleachings in 1998 and 2010. However, reefs that experience a severe bleaching event become resistant to future heat-induced bleaching, due to rapid directional selection. Similar rapid adaption may protect coral reefs from global warming.
A large-scale systematic study of the Jarvis Island coral community, which experienced ten El Niño-coincident coral bleaching events from 1960 to 2016, found that the reef recovered from almost complete death after severe events.
Protection
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Marine protected areas (MPAs) are areas designated because they provide various kinds of protection to ocean and/or estuarine areas. They are intended to promote responsible fishery management and habitat protection. MPAs can also encompass social and biological objectives, including reef restoration, aesthetics, biodiversity and economic benefits.
The effectiveness of MPAs is still debated. For example, a study investigating the success of a small number of MPAs in Indonesia, the Philippines and Papua New Guinea found no significant differences between the MPAs and unprotected sites. Furthermore, in some cases they can generate local conflict, due to a lack of community participation, clashing views of the government and fisheries, effectiveness of the area and funding. In some situations, as in the Phoenix Islands Protected Area, MPAs provide revenue to locals. The level of income provided is similar to the income they would have generated without controls. Overall, it appears the MPA's can provide protection to local coral reefs, but that clear management and sufficient funds are required.
The Caribbean Coral Reefs – Status Report 1970–2012, states that coral decline may be reduced or even reversed. For this overfishing needs to be stopped, especially fishing on species key to coral reefs, such as parrotfish. Direct human pressure on coral reefs should also be reduced and the inflow of sewage should be minimised. Measures to achieve this could include restricting coastal settlement, development and tourism. The report shows that healthier reefs in the Caribbean are those with large, healthy populations of parrotfish. These occur in countries that protect parrotfish and other species, like sea urchins. They also often ban fish trapping and spearfishing. Together these measures help creating "resilient reefs".
Protecting networks of diverse and healthy reefs, not only climate refugia, helps ensure the greatest chance of genetic diversity, which is critical for coral to adapt to new climates. A variety of conservation methods applied across marine and terrestrial threatened ecosystems makes coral adaption more likely and effective.
Designating a reef as a biosphere reserve, marine park, national monument or world heritage site can offer protections. For example, Belize's barrier reef, Sian Ka'an, the Galapagos islands, Great Barrier Reef, Henderson Island, Palau and Papahānaumokuākea Marine National Monument are world heritage sites.
In Australia, the Great Barrier Reef is protected by the Great Barrier Reef Marine Park Authority, and is the subject of much legislation, including a biodiversity action plan. Australia compiled a Coral Reef Resilience Action Plan. This plan consists of adaptive management strategies, including reducing carbon footprint. A public awareness plan provides education on the "rainforests of the sea" and how people can reduce carbon emissions.
Inhabitants of Ahus Island, Manus Province, Papua New Guinea, have followed a generations-old practice of restricting fishing in six areas of their reef lagoon. Their cultural traditions allow line fishing, but no net or spear fishing. Both biomass and individual fish sizes are significantly larger than in places where fishing is unrestricted.
Increased levels of atmospheric CO2 contribute to ocean acidification, which in turn damages coral reefs. To help combat ocean acidification, several countries have put laws in place to reduce greenhouse gases such as carbon dioxide. Many land use laws aim to reduce CO2 emissions by limiting deforestation. Deforestation can release significant amounts of CO2 absent sequestration via active follow-up forestry programs. Deforestation can also cause erosion, which flows into the ocean, contributing to ocean acidification. Incentives are used to reduce miles traveled by vehicles, which reduces carbon emissions into the atmosphere, thereby reducing the amount of dissolved CO2 in the ocean. State and federal governments also regulate land activities that affect coastal erosion. High-end satellite technology can monitor reef conditions.
The United States Clean Water Act puts pressure on state governments to monitor and limit run-off of polluted water.
Restoration
See also: Aquaculture of coral, Artificial reef, and Restoration ecologyCoral reef restoration has grown in prominence over the past several decades because of the unprecedented reef die-offs around the planet. Coral stressors can include pollution, warming ocean temperatures, extreme weather events, and overfishing. With the deterioration of global reefs, fish nurseries, biodiversity, coastal development and livelihood, and natural beauty are under threat. Fortunately, researchers have taken it upon themselves to develop a new field, coral restoration, in the 1970s–1980s
Coral farming
Coral aquaculture, also known as coral farming or coral gardening, is showing promise as a potentially effective tool for restoring coral reefs. The "gardening" process bypasses the early growth stages of corals when they are most at risk of dying. Coral seeds are grown in nurseries, then replanted on the reef. Coral is farmed by coral farmers whose interests range from reef conservation to increased income. Due to its straight forward process and substantial evidence of the technique having a significant effect on coral reef growth, coral nurseries became the most widespread and arguably the most effective method for coral restoration.
Coral gardens take advantage of a coral's natural ability to fragment and continuing to grow if the fragments are able to anchor themselves onto new substrates. This method was first tested by Baruch Rinkevich in 1995 which found success at the time. By today's standards, coral farming has grown into a variety of different forms, but still has the same goals of cultivating corals. Consequently, coral farming quickly replaced previously used transplantation methods or the act of physically moving sections or whole colonies of corals into a new area. Transplantation has seen success in the past and decades of experiments have led to a high success and survival rate. However, this method still requires the removal of corals from existing reefs. With the current state of reefs, this kind of method should generally be avoided if possible. Saving healthy corals from eroding substrates or reefs that are doomed to collapse could be a major advantage of utilizing transplantation.
Coral gardens generally take on the safe forms no matter where you go. It begins with the establishment of a nursery where operators can observe and care for coral fragments. It goes without saying that nurseries should be established in areas that are going to maximize growth and minimize mortality. Floating offshore coral trees or even aquariums are possible locations where corals can grow. After a location has been determined, collection and cultivation can occur.
The major benefit of using coral farms is it lowers polyp and juvenile mortality rates. By removing predators and recruitment obstacles, corals are able to mature without much hindrance. However, nurseries cannot stop climate stressors. Warming temperatures or hurricanes can still disrupt or even kill nursery corals.
Technology is becoming more popular in the coral farming process. Teams from the Reef Restoration and Adaptation Program (RRAP) have trialled coral counting technology utilizing a prototype robotic camera. The camera uses computer vision and learning algorithms to detect and count individual coral babies and track their growth and health in real time. This technology, with research led by QUT, is intended to be used during annual coral spawning events and will provide researchers with control that is not currently possible when mass-producing corals.
Creating substrates
Efforts to expand the size and number of coral reefs generally involve supplying substrate to allow more corals to find a home. Substrate materials include discarded vehicle tires, scuttled ships, subway cars and formed concrete, such as reef balls. Reefs grow unaided on marine structures such as oil rigs. In large restoration projects, propagated hermatypic coral on substrate can be secured with metal pins, superglue or milliput. Needle and thread can also attach A-hermatype coral to substrate.
Biorock is a substrate produced by a patented process that runs low voltage electrical currents through seawater to cause dissolved minerals to precipitate onto steel structures. The resultant white carbonate (aragonite) is the same mineral that makes up natural coral reefs. Corals rapidly colonize and grow at accelerated rates on these coated structures. The electrical currents also accelerate the formation and growth of both chemical limestone rock and the skeletons of corals and other shell-bearing organisms, such as oysters. The vicinity of the anode and cathode provides a high-pH environment which inhibits the growth of competitive filamentous and fleshy algae. The increased growth rates fully depend on the accretion activity. Under the influence of the electric field, corals display an increased growth rate, size and density.
Simply having many structures on the ocean floor is not enough to form coral reefs. Restoration projects must consider the complexity of the substrates they are creating for future reefs. Researchers conducted an experiment near Ticao Island in the Philippines in 2013 where several substrates in varying complexities were laid in the nearby degraded reefs. Large complexity consisted of plots that had both a human-made substrates of both smooth and rough rocks with a surrounding fence, medium consisted of only the human-made substrates, and small had neither the fence or substrates. After one month, researchers found that there was a positive correlation between structure complexity and recruitment rates of larvae. The medium complexity performed the best with larvae favoring rough rocks over smooth rocks. Following one year of their study, researchers visited the site and found that many of the sites were able to support local fisheries. They came to the conclusion that reef restoration could be done cost-effectively and will yield long term benefits given they are protected and maintained.
Relocation
One case study with coral reef restoration was conducted on the island of Oahu in Hawaii. The University of Hawaii operates a Coral Reef Assessment and Monitoring Program to help relocate and restore coral reefs in Hawaii. A boat channel from the island of Oahu to the Hawaii Institute of Marine Biology on Coconut Island was overcrowded with coral reefs. Many areas of coral reef patches in the channel had been damaged from past dredging in the channel.
Dredging covers corals with sand. Coral larvae cannot settle on sand; they can only build on existing reefs or compatible hard surfaces, such as rock or concrete. Because of this, the university decided to relocate some of the coral. They transplanted them with the help of United States Army divers, to a site relatively close to the channel. They observed little if any damage to any of the colonies during transport and no mortality of coral reefs was observed on the transplant site. While attaching the coral to the transplant site, they found that coral placed on hard rock grew well, including on the wires that attached the corals to the site.
No environmental effects were seen from the transplantation process, recreational activities were not decreased, and no scenic areas were affected.
As an alternative to transplanting coral themselves, juvenile fish can also be encouraged to relocate to existing coral reefs by auditory simulation. In damaged sections of the Great Barrier Reef, loudspeakers playing recordings of healthy reef environments were found to attract fish twice as often as equivalent patches where no sound was played, and also increased species biodiversity by 50%.
Heat-tolerant symbionts
Another possibility for coral restoration is gene therapy: inoculating coral with genetically modified bacteria, or naturally-occurring heat-tolerant varieties of coral symbiotes, may make it possible to grow corals that are more resistant to climate change and other threats. Warming oceans are forcing corals to adapt to unprecedented temperatures. Those that do not have a tolerance for the elevated temperatures experience coral bleaching and eventually mortality. There is already research that looks to create genetically modified corals that can withstand a warming ocean. Madeleine J. H. van Oppen, James K. Oliver, Hollie M. Putnam, and Ruth D. Gates described four different ways that gradually increase in human intervention to genetically modify corals. These methods focus on altering the genetics of the zooxanthellae within coral rather than the alternative.
The first method is to induce acclimatization of the first generation of corals. The idea is that when adult and offspring corals are exposed to stressors, the zooxanthellae will gain a mutation. This method is based mostly on the chance that the zooxanthellae will acquire the specific trait that will allow it to better survive in warmer waters. The second method focuses on identifying what different kinds of zooxanthellae are within the coral and configuring how much of each zooxanthella lives within the coral at a given age. Use of zooxanthellae from the previous method would only boost success rates for this method. However, this method would only be applicable to younger corals, for now, because previous experiments of manipulation zooxanthellae communities at later life stages have all failed. The third method focuses on selective breeding tactics. Once selected, corals would be reared and exposed to simulated stressors in a laboratory. The last method is to genetically modify the zooxanthellae itself. When preferred mutations are acquired, the genetically modified zooxanthellae will be introduced to an aposymbiotic poly and a new coral will be produced. This method is the most laborious of the fourth, but researchers believe this method should be utilized more and holds the most promise in genetic engineering for coral restoration.
Invasive algae
Hawaiian coral reefs smothered by the spread of invasive algae were managed with a two-prong approach: divers manually removed invasive algae, with the support of super-sucker barges. Grazing pressure on invasive algae needed to be increased to prevent the regrowth of the algae. Researchers found that native collector urchins were reasonable candidate grazers for algae biocontrol, to extirpate the remaining invasive algae from the reef.
Invasive algae in Caribbean reefs
Macroalgae, or better known as seaweed, has to potential to cause reef collapse because they can outcompete many coral species. Macroalgae can overgrow on corals, shade, block recruitment, release biochemicals that can hinder spawning, and potentially form bacteria harmful to corals. Historically, algae growth was controlled by herbivorous fish and sea urchins. Parrotfish are a prime example of reef caretakers. Consequently, these two species can be considered as keystone species for reef environments because of their role in protecting reefs.
Before the 1980s, Jamaica's reefs were thriving and well cared for, however, this all changed after Hurricane Allen occurred in 1980 and an unknown disease spread across the Caribbean. In the wake of these events, massive damage was caused to both the reefs and sea urchin population across Jamaican's reefs and into the Caribbean Sea. As little as 2% of the original sea urchin population survived the disease. Primary macroalgae succeeded the destroyed reefs and eventually larger, more resilient macroalgae soon took its place as the dominant organism. Parrotfish and other herbivorous fish were few in numbers because of decades of overfishing and bycatch at the time. Historically, the Jamaican coast had 90% coral cover and was reduced to 5% in the 1990s. Eventually, corals were able to recover in areas where sea urchin populations were increasing. Sea urchins were able to feed and multiply and clear off substrates, leaving areas for coral polyps to anchor and mature. However, sea urchin populations are still not recovering as fast as researchers predicted, despite being highly fecundate. It is unknown whether or not the mysterious disease is still present and preventing sea urchin populations from rebounding. Regardless, these areas are slowly recovering with the aid of sea urchin grazing. This event supports an early restoration idea of cultivating and releasing sea urchins into reefs to prevent algal overgrowth.
Microfragmentation and fusion
In 2014, Christopher Page, Erinn Muller, and David Vaughan from the International Center for Coral Reef Research & Restoration at Mote Marine Laboratory in Summerland Key, Florida developed a new technology called "microfragmentation", in which they use a specialized diamond band saw to cut corals into 1 cm fragments instead of 6 cm to advance the growth of brain, boulder, and star corals. Corals Orbicella faveolata and Montastraea cavernosa were outplanted off the Florida's shores in several microfragment arrays. After two years, O. faveolata had grown 6.5x its original size while M. cavernosa had grown nearly twice its size. Under conventional means, both corals would have required decades to reach the same size. It is suspected that if predation events had not occurred near the beginning of the experiment O. faveolata would have grown at least ten times its original size. By using this method, Mote Marine Laboratory successfully generated 25,000 corals within a single year, subsequently transplanting 10,000 of them into the Florida Keys. Shortly after, they discovered that these microfragments fused with other microfragments from the same parent coral. Typically, corals that are not from the same parent fight and kill nearby corals in an attempt to survive and expand. This new technology is known as "fusion" and has been shown to grow coral heads in just two years instead of the typical 25–75 years. After fusion occurs, the reef will act as a single organism rather than several independent reefs. Currently, there has been no published research into this method.
See also
- Deep-water coral — Corals living in the cold waters of deeper, darker parts of the oceans
- Mesophotic coral reef — Corals living in the mesopelagic or twilight zone
- Fossil Coral Reef – National Natural Landmark in Le Roy, New York
- Census of Coral Reefs – Field project of the Census of Marine Life
- Catlin Seaview Survey
- Coral reef organizations – U.S. Coral Reef Task ForcePages displaying wikidata descriptions as a fallback
- Sponge reef – Reefs produced by sea sponges.
- Pseudo-atoll – Island that encircles a lagoon
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Further references
- Coral Reef Protection: What Are Coral Reefs?. US EPA.
- UNEP. 2004. Coral Reefs in the South China Sea. UNEP/GEF/SCS Technical Publication No. 2.
- UNEP. 2007. Coral Reefs Demonstration Sites in the South China Sea. UNEP/GEF/SCS Technical Publication No. 5.
- UNEP, 2007. National Reports on Coral Reefs in the Coastal Waters of the South China Sea. UNEP/GEF/SCS Technical Publication No. 11.
External links
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Coral Reefs: Rainforests of the Sea ORG Educational films. |
- "Coral Reef Factsheet". Waitt Institute. Archived from the original on 9 June 2015. Retrieved 8 June 2015.
- Corals and Coral Reefs overview at the Smithsonian Ocean Portal
- About Corals Archived 26 December 2013 at the Wayback Machine Australian Institute of Marine Science.
- International Coral Reef Initiative
- Moorea Coral Reef Long Term Ecological Research Site (US NSF)
- ARC Centre of Excellence for Coral Reef Studies
- NOAA's Coral-List Listserver for Coral Reef Information and News
- NOAA's Coral Reef Conservation Program
- NOAA's Coral Reef Information System
- ReefBase: A Global Information System on Coral Reefs Archived 31 August 2012 at the Wayback Machine
- National Coral Reef Institute Archived October 23, 2012, at the Wayback Machine Nova Southeastern University
- Marine Aquarium Council Archived 24 July 2013 at the Wayback Machine
- NCORE National Center for Coral Reef Research University of Miami
- Science and Management of Coral Reefs in the South China Sea and Gulf of Thailand
- Microdocs Archived 27 July 2011 at the Wayback Machine: 4 kinds of Reef Archived 24 October 2012 at the Wayback Machine & Reef structure Archived 24 October 2012 at the Wayback Machine
- Reef Relief Active Florida environmental non-profit focusing on coral reef education and protection
- Global Reef Record – Catlin Seaview Survey of reef, a database of images and other information
- "Corals and Coral Reefs" (archived). Nancy Knowlton, iBioSeminars, 2011.
- Nancy Knowlton's Seminar: "Corals and Coral Reefs". Nancy Knowlton, iBioSeminars, 2011.
- About coral reefs Living Reefs Foundation, Bermuda
- Caribbean Coral Reefs – Status Report 1970-2012 by the IUCN. – Video on YouTube, featuring the report.
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