Editing Coral reef (section)

==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. [https://www.livingoceansfoundation.org/wp-content/uploads/2015/04/U10-Reef-Types-Background.pdf ''Unit 10: Reef Types''] 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>

===Fringing reef===
[[File:EilatFringingReef.jpg|thumb|left|Fringing reef at [[Eilat]] at the southern tip of [[Israel]]]]
{{main|Fringing reef}}
[[File:Saumriff1.png|thumb|Fringing reef]]
A fringing reef, also called a shore reef,<ref name=CRISG/> is directly attached to a shore,<ref>[https://www.pmfias.com/coral-reef-fringing-reefs-barrier-reefs-atolls/ ''Fringing Reefs (Shore Reefs)''] 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>[https://coral.org/coral-reefs-101/coral-reef-ecology/types-of-coral-reef-formations/ ''Types of Coral Reef Formations''] 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&nbsp;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 [[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, with outer regions pushed far out into the sea, the inner part is deepened by erosion and eventually forms a [[lagoon]].<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&nbsp;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.<ref>Hanauer, Eric. ''The Egyptian Red Sea: A Diver's Guide''. San Diego: Watersport, 1988, p. 74.</ref>

===Barrier reef===
[[File:Barriereriff.png|thumb|Barrier reef]]
Barrier reefs are separated from a mainland or island shore by a deep channel or [[lagoon]].<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&nbsp;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]].<ref name=CRA/><ref name=CRI>[https://www.coral-reef-info.com/types-of-coral-reefs.html ''Types of Coral Reefs''] {{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 [[Mesoamerican Barrier Reef System]] and the [[New Caledonian Barrier Reef]].<ref name=CRI/> Barrier reefs are also found on the coasts of [[Providencia (Colombia)|Providencia]],<ref name=CRI/> [[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===
[[File:Plattformriff.png|thumb|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.<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.&nbsp;1–85, pls.&nbsp;1–17 |date=Apr 1978}}</ref> on the continental shelf, about 100–200&nbsp;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.<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 [[Red Sea]] near [[Jeddah]]. 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 [[Lakshadweep|Laccadives]] are U-shaped, due to wind and water flow.

===Atoll===
{{main|Atoll}}
[[File:Coral atoll formation animation.gif|thumb|Formation of an atoll according to [[Charles Darwin]]]]
Atolls or [[atoll reef]]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 [[erosion|erodes]] 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 [[Caroline Islands]], the [[Cook Islands]], [[French Polynesia]], the [[Marshall Islands]] and [[Micronesia]].<ref name=CRI/>

Atolls are found in the Indian Ocean, for example, in the [[Maldives]], the [[Chagos Islands]], the [[Seychelles]] and around [[Cocos Island]].<ref name=CRI/> The entire Maldives consist of 26 atolls.<ref>[http://www.mymaldives.com/maldives/atolls/ ''Maldives Atolls''] at www.mymaldives.com. Retrieved 2 Feb 2018.</ref>

===Other reef types or variants===
[[File:Maldives small island.jpg|thumb|right|A small [[atoll]] in the [[Maldives]]]]
[[File:Maldives - Kurumba Island.jpg|thumb|right|Inhabited [[cay]] in the [[Maldives]]]]

* '''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>
* '''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 [[lagoon]] or [[embayment]], often circular and surrounded by sand or [[seagrass]]. 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 [[Red Sea]]; does not reach near enough to the surface to cause visible [[Breaking wave|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 [[Radiocarbon dating|radioactive carbon dating]] and have been used to reconstruct [[Holocene]] [[sea level]]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>
* '''[[Cay]]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 [[Pacific Ocean|Pacific]], [[Atlantic Ocean|Atlantic]] and [[Indian Ocean]]s (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