Old page wikitext, before the edit (old_wikitext) | '{{other uses}}
{{Taxobox
| name = Coral
| fossil_range = {{Fossil range|Cambrian|Recent}}
| image = Coral Outcrop Flynn Reef.jpg
| image_caption = A coral outcrop on the [[Great Barrier Reef]], [[Australia]]
| regnum = [[Animal]]ia
| phylum = [[Cnidaria]]
| classis = [[Anthozoa]]
| classis_authority = [[Christian Gottfried Ehrenberg|Ehrenberg]], 1831
| subdivision_ranks = Extant subclasses and orders
| subdivision =
* [[Octocorallia]]<ref>{{cite WoRMS |author= Hoeksema, Bert |year=2015 |title=Octocorallia |id=1341 |accessdate=2015-04-24 }}</ref>
** [[Alcyonacea]]
** [[Helioporacea]]
** [[Pennatulacea]]
* [[Hexacorallia]]<ref>{{cite WoRMS |author= Hoeksema, Bert |year=2015 |title=Hexacorallia |id=1340 |accessdate=2015-04-24 }}</ref>
** [[Actiniaria]]
** [[Antipatharia]]
** [[Corallimorpharia]]
** [[Scleractinia]]
** [[Zoantharia]]
* [[Ceriantharia]]<ref>{{cite WoRMS |author= Hoeksema, Bert |year=2016 |title=Ceriantharia |id=1361 |accessdate=2017-02-04 }}</ref>
** [[Penicillaria]]
** [[Spirularia]]
}}
'''Corals''' are [[marine invertebrates]] in the [[class (biology)|class]] [[Anthozoa]] of [[phylum]] [[Cnidaria]]. They typically live in compact [[Colony (biology)|colonies]] of many identical individual [[polyp]]s. The group includes the important [[Coral reef|reef]] builders that inhabit tropical [[ocean]]s and secrete [[calcium carbonate]] to form a hard skeleton.
A coral "group" is a colony of myriad [[cloning|genetically identical]] polyps. Each polyp is a sac-like animal typically only a few millimeters in diameter and a few centimeters in length. A set of [[tentacle]]s surround a central mouth opening. An [[exoskeleton]] is excreted near the base. Over many generations, the colony thus creates a large skeleton that is characteristic of the species. Individual heads grow by [[asexual reproduction]] of polyps. Corals also breed sexually by spawning: polyps of the same species release [[gamete]]s simultaneously over a period of one to several nights around a [[full moon]].
Although some corals can catch small [[fish]] and [[plankton]] using [[Cnidocyte|stinging cells]] on their tentacles, most corals obtain the majority of their energy and nutrients from [[photosynthesis|photosynthetic]] [[unicellular]] [[dinoflagellate]]s in the genus ''[[Symbiodinium]]'' that live within their tissues. These are commonly known as [[zooxanthellae]] and the corals that contain them are zooxanthellate corals. Such corals require sunlight and grow in clear, shallow water, typically at depths shallower than {{convert|60|m}}. Corals are major contributors to the physical structure of the [[coral reef]]s that develop in tropical and subtropical waters, such as the enormous [[Great Barrier Reef]] off the coast of [[Queensland]], Australia.
Other corals do not rely on zooxanthellae and can live in much deeper water, with the cold-water [[genus]] ''[[Lophelia]]'' surviving as deep as {{convert|3000|m}}.<ref name=Squires>{{cite journal | author=Squires, D.F. | year=1959 | title=Deep sea corals collected by the Lamont Geological Observatory. 1. Atlantic corals | journal = American Museum Novitates | volume=1965 | pages=1–42}}</ref> Some have been found on the [[Darwin Mounds]], north-west of [[Cape Wrath]], Scotland. Corals have also been found as far north as off the coast of [[Washington (state)|Washington State]] and the [[Aleutian Islands]].
{{TOC limit|3}}
==Taxonomy==
{{cladogram|title=
|caption=Phylogeny of Anthozoa
|clades={{clade| style=font-size:85%;line-height:75%
|label1= [[Hexacorallia]]
|1={{clade
|1=[[Actiniaria]]
|2=[[Antipatharia]]
|3=[[Corallimorpharia]]
|4=[[Scleractinia]]
|5=[[Zoantharia]]
}}
|label2= [[Octocorallia]]
|2={{clade
|1=[[Alcyonacea]]
|2=[[Helioporacea]]
|3=[[Pennatulacea]]
}}
|label3= [[Ceriantharia]]
|3={{clade
|1=[[Penicillaria]]
|2=[[Spirularia]]
}}
}}
}}
In his ''Scala Naturae'', [[Aristotle]] classified corals as "zoophyta" ("plant-animals"), animals that had characteristics of plants and were therefore hypothetically in between animals and plants. The Persian polymath [[Al-Biruni]] (d. 1048) classified sponges and corals as animals, arguing that they respond to touch.<ref name="Egerton">{{cite book |last=Egerton |first=Frank N. |title=Roots of Ecology: Antiquity to Haeckel |year=2012 |publisher=University of California Press |isbn=0-520-95363-0 |page=24}}</ref> Nevertheless, people believed corals to be plants until the eighteenth century, when [[William Herschel]] used a microscope to establish that coral had the characteristic thin cell membranes of an [[animal]].<ref name=Ep2>''[[The Light of Reason]]'' 8 August 2006 02:00 BBC Four</ref>
The [[phylogeny]] of Anthozoans is not clearly understood and a number of different models have been proposed. Within the Hexacorallia, the sea anemones, coral anemones and stony corals may constitute a [[monophyletic]] grouping united by their eight-fold [[Symmetry in biology|symmetry]] and [[cnidocyte]] trait. The Octocorallia appears to be monophyletic, and primitive members of this group may have been [[stolon]]ate.<ref name=Ruppert /> The [[cladogram]] presented here comes from a 2014 study by Stampar ''et al.'' which was based on the divergence of [[mitochondrial DNA]] within the group and on nuclear markers.<ref name=Stampar />
Corals are classified in the [[class (biology)|class]] [[Anthozoa]] of the [[phylum]] [[Cnidaria]]. They are divided into three subclasses, [[Hexacorallia]], [[Octocorallia]],<ref>{{cite WoRMS |author= Hoeksema, Bert |year=2015 |title=Anthozoa |id=1292 |accessdate=2015-04-24|db=}}</ref> and [[Tube-dwelling anemone|Ceriantharia]].<ref name=Stampar>{{cite journal |author1=Stampar, S.N. |author2=Maronna, M.M. |author3=Kitahara, M.V. |author4=Reimer, J.D. |author5=Morandini, A.C. |year=2014 | title = Fast-Evolving Mitochondrial DNA in Ceriantharia: A Reflection of Hexacorallia Paraphyly? | journal = PLoS ONE | volume = 9 | issue = 1 | pages = e86612 | pmid = 24475157 | doi=10.1371/journal.pone.0086612 | pmc=3903554 }}</ref><ref name=Chen>{{cite journal |author1=Chen, C. A. |author2=Odorico, D. M. |author3=ten Lohuis, M. |author4=Veron, J. E. N. |author5=Miller, D. J. |year=1995 | title = Systematic relationships within the Anthozoa (Cnidaria: Anthozoa) using the 5'-end of the 28S rDNA | journal = Molecular Phylogenetics and Evolution | volume = 4 | issue = 2 | pages = 175–83 | pmid = 7663762 | url = http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B6WNH-45R889V-14-1&_cdi=6963&_user=10&_orig=search&_coverDate=06%2F30%2F1995&_qd=1&_sk=999959997&view=c&wchp=dGLbVzz-zSkzV&md5=531282d4acffe5b53431d2dcb91df8a8&ie=/sdarticle.pdf | doi = 10.1006/mpev.1995.1017}}</ref> The Hexacorallia include the stony corals, the [[sea anemone]]s and the [[zoanthids]]. These groups have [[polyp]]s that generally have 6-fold symmetry. The Octocorallia include [[blue coral]], [[soft coral]]s, [[sea pen]]s, and [[gorgonian]]s (sea fans and sea whips). These groups have polyps with 8-fold symmetry, each polyp having eight tentacles and eight [[Mesentery (zoology)|mesenteries]]. Ceriantharia are the tube-dwelling anemones.<ref name=Ruppert>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |pages=132–48 }}</ref>
[[Fire coral]]s are not true corals, being in the order [[Anthomedusa]] (sometimes known as Anthoathecata) of the class [[Hydrozoa]].<ref>{{cite WoRMS |author=Schuchert, Peter |year=2015 |title=Milleporidae Fleming, 1828 |id=196235 |accessdate=2015-04-24 }}</ref>
==Anatomy==
[[File:Coral polyp.jpg|thumb|Anatomy of a stony coral polyp]]
Corals are [[Sessility (motility)|sessile]] animals in the class [[Anthozoa]] and differ from most other cnidarians in not having a [[Medusa (biology)|medusa]] stage in their life cycle. The body unit of the animal is a [[polyp]]. Most corals are colonial, the initial polyp budding to produce another and the colony gradually developing from this small start. In stony corals, also known as hard corals, the polyps produce a skeleton composed of [[calcium carbonate]] to strengthen and protect the organism. This is deposited by the polyps and by the [[coenosarc]], the living tissue that connects them. The polyps sit in cup-shaped depressions in the skeleton known as [[corallite]]s. Colonies of stony coral are very variable in appearance; a single species may adopt an encrusting, plate-like, bushy, columnar or massive solid structure, the various forms often being linked to different types of habitat, with variations in light level and water movement being significant.<ref name=Ruppert/>
In soft corals, there is no stony skeleton but the tissues are often toughened by the presence of tiny skeletal elements known as sclerites, which are made from calcium carbonate. Soft corals are very variable in form and most are colonial. A few soft corals are [[stolon]]ate, but the polyps of most are connected by sheets of coenosarc. In some species this is thick and the polyps are deeply embedded. Some soft corals are encrusting or form lobes. Others are tree-like or whip-like and have a central axial skeleton embedded in the tissue matrix. This is composed either of a fibrous protein called [[gorgonin]] or of a calcified material. In both stony and soft corals, the polyps can be retracted, with stony corals relying on their hard skeleton and [[cnidocyte]]s for defence against predators, with soft corals generally relying on chemical defences in the form of toxic substances present in the tissues known as [[terpenoid]]s.<ref name=Ruppert/>
[[File:Montastrea cavernosa.jpg|thumb|''[[Montastraea cavernosa]]'' polyps with tentacles extended]]
The polyps of stony corals have six-fold symmetry while those of soft corals have eight. The mouth of each polyp is surrounded by a ring of tentacles. In stony corals these are cylindrical and taper to a point, but in soft corals they are pinnate with side branches known as pinnules. In some tropical species these are reduced to mere stubs and in some they are fused to give a paddle-like appearance.<ref name=Sprung>{{cite book |title=Corals: A quick reference guide |last=Sprung |first=Julian |year=1999 |publisher=Ricordea Publishing |isbn=1-883693-09-8 |page=145 }}</ref> In most corals, the tentacles are retracted by day and spread out at night to catch plankton and other small organisms. Shallow water species of both stony and soft corals can be [[zooxanthella]]te, the corals supplementing their plankton diet with the products of photosynthesis produced by these [[Symbiosis|symbionts]].<ref name=Ruppert/> The polyps interconnect by a complex and well-developed system of [[gastrovascular]] canals, allowing significant sharing of nutrients and symbionts.<ref name=Gateno>{{cite journal |author1=D. Gateno |author2=A. Israel |author3=Y. Barki |author4=B. Rinkevich | title=Gastrovascular Circulation in an Octocoral: Evidence of Significant Transport of Coral and Symbiont Cells | journal=The Biological Bulletin | year=1998 | pages=178–86 | volume=194 | issue=2 | url=http://www.biolbull.org/cgi/reprint/194/2/178 | doi=10.2307/1543048 | jstor=1543048 | publisher=Marine Biological Laboratory}}</ref>
==Ecology==
===Feeding===
Polyps feed on a variety of small organisms, from microscopic zooplankton to small fish. The polyp's tentacles immobilize or kill prey using their nematocysts. These cells carry [[venom]] which they rapidly release in response to contact with another organism. A dormant nematocyst discharges in response to nearby prey touching the trigger (cnidocil). A flap (operculum) opens and its stinging apparatus fires the barb into the prey. The venom is injected through the hollow filament to immobilise the prey; the tentacles then manoeuvre the prey to the mouth.<ref>{{cite web |title=Coral Feeding Habits |url=http://coralreef.noaa.gov/aboutcorals/coral101/feedinghabits/ |publisher=NOAA |accessdate=25 April 2015}}</ref>
The tentacles then contract to bring the prey into the stomach. Once the prey is digested, the stomach reopens, allowing the elimination of waste products and the beginning of the next hunting cycle. They can scavenge drifting organic molecules and dissolved organic molecules.<ref name=murph/>{{rp|24}}
===Intracellular symbionts===
Many corals, as well as other [[cnidaria]]n groups such as ''[[Aiptasia]]'' (a [[sea anemone]]) form a [[symbiotic]] relationship with a class of [[dinoflagellate]] [[algae]], [[zooxanthellae]] of the genus ''[[Symbiodinium]]''.<ref name=murph/>{{rp|24}} ''Aiptasia'', a familiar pest among coral reef aquarium hobbyists, serves as a valuable [[model organism]] in the study of cnidarian-algal symbiosis. Typically, each polyp harbors one species of algae. Via photosynthesis, these provide energy for the coral, and aid in [[calcification]].<ref name=MilneBay>{{cite web|author1=Madl, P. |author2=Yip, M. | year = 2000 | url = http://biophysics.sbg.ac.at/png/png3.htm | title = Field Excursion to Milne Bay Province – Papua New Guinea| accessdate = 2006-03-31}}</ref> As much as 30% of the tissue of a polyp may be algal material.<ref name=murph>{{cite book |title=Coral Reefs: Cities Under The Seas |last=Murphy |first=Richard C. |year=2002 |isbn=0-87850-138-X |publisher=The Darwin Press}}</ref>{{rp|23}}
The algae benefit from a safe place to live and consume the polyp's [[carbon dioxide]] and nitrogenous waste. Due to the strain the algae can put on the polyp, stress on the coral often drives them to eject the algae. Mass ejections are known as [[coral bleaching]], because the algae contribute to coral's brown coloration; other colors, however, are due to host coral pigments, such as [[green fluorescent protein]]s (GFPs). Ejection increases the polyp's chance of surviving short-term stress—they can regain algae, possibly of a different species at a later time. If the stressful conditions persist, the polyp eventually dies.<ref name=Toller>{{cite journal |author1=W. W. Toller |author2=R. Rowan |author3=N. Knowlton | title=Repopulation of Zooxanthellae in the Caribbean Corals ''Montastraea annularis'' and ''M. faveolata'' following Experimental and Disease-Associated Bleaching | journal=The Biological Bulletin | year=2001 | pages=360–73 | volume=201 | url=http://www.biolbull.org/cgi/content/full/201/3/360 | doi = 10.2307/1543614 | pmid=11751248 | issue=3 | jstor=1543614 | publisher=Marine Biological Laboratory}}</ref>
==Reproduction==
Corals can be both [[Gonochorism|gonochoristic]] (unisexual) and [[Hermaphroditism|hermaphroditic]], each of which can reproduce sexually and asexually. Reproduction also allows coral to settle in new areas.
===Sexual===
[[File:Coral Life Cycles ZP.svg|thumb|400px|Life cycles of broadcasters and brooders]]
Corals predominantly reproduce [[sexual reproduction|sexually]]. About 25% of [[hermatypic coral]]s (stony corals) form single sex ([[gonochoristic]]) colonies, while the rest are [[hermaphroditic]].<ref name=Veron>{{cite book | author = Veron, J.E.N. | year = 2000
| title = Corals of the World. Vol 3 | edition = 3rd | publisher = Australian Institute of Marine Sciences and CRR Qld Pty Ltd.
| location = Australia | isbn = 0-642-32236-8}}</ref>
====Broadcasters====
About 75% of all hermatypic corals "broadcast spawn" by releasing [[gamete]]s—[[egg (biology)|eggs]] and [[sperm]]—into the water to spread offspring. The gametes fuse during fertilization to form a microscopic [[larva]] called a [[planula]], typically pink and elliptical in shape. A typical coral colony forms several thousand larvae per year to overcome the odds against formation of a new colony.<ref name=Barnes99>{{cite book | last1= Barnes |first1=R. and |first2=R. |last2=Hughes | year = 1999 | title = An Introduction to Marine Ecology | edition = 3rd | pages = 117–41 | publisher = Blackwell | location = Malden, MA | isbn = 0-86542-834-4}}</ref>
[[File:Stony coral spawning 2.jpg|thumb|A male [[great star coral]], ''Montastraea cavernosa'', releasing sperm into the water.]]
[[Reproductive synchrony|Synchronous spawning]] is very typical on the coral reef, and often, even when multiple [[species]] are present, all corals spawn on the same night. This synchrony is essential so male and female gametes can meet. Corals rely on environmental cues, varying from species to species, to determine the proper time to release gametes into the water. The cues involve temperature change, [[Lunar phase|lunar cycle]], [[day length]], and possibly chemical signalling.<ref name=Veron /> Synchronous spawning may form hybrids and is perhaps involved in coral [[speciation]].<ref name=Hatta>{{cite journal |author1=Hatta, M. |author2=Fukami, H. |author3=Wang, W. |author4=Omori, M. |author5=Shimoike, K. |author6=Hayashibara, T. |author7=Ina, Y. |author8=Sugiyama, T. | title=Reproductive and genetic evidence for a reticulate evolutionary theory of mass spawning corals | journal=Molecular Biology and Evolution | year=1999 | pages=1607–13 | volume=16 | issue=11 | url=http://mbe.oxfordjournals.org/content/16/11/1607.full.pdf | format=PDF | pmid=10555292 | doi=10.1093/oxfordjournals.molbev.a026073}}</ref> The immediate cue is most often sunset, which cues the release.<ref name=Veron /> The spawning event can be visually dramatic, clouding the usually clear water with gametes.
====Brooders====
Brooding species are most often ahermatypic (not reef-building) in areas of high current or wave action. Brooders release only sperm, which is negatively buoyant, sinking on to the waiting egg carriers who harbor unfertilized eggs for weeks. Synchronous spawning events sometimes occurs even with these species.<ref name=Veron /> After fertilization, the corals release planula that are ready to settle.<ref name=MilneBay />
====Planulae====
[[Planula]] larvae exhibit positive [[phototaxis]], swimming towards light to reach surface waters, where they drift and grow before descending to seek a hard surface to which they can attach and begin a new colony. They also exhibit positive [[sonotaxis]], moving towards sounds that emanate from the reef and away from open water.<ref>{{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. |year=2010 |title=Coral Larvae Move toward Reef Sounds |journal=PLoS ONE |volume=5 |issue=5 |pages=e10660 |pmid=20498831 |doi=10.1371/journal.pone.0010660 |laysummary=http://www.sciencedaily.com/releases/2010/05/100514171908.htm |laysource=ScienceDaily |laydate=May 16, 2010 |pmc=2871043}}</ref> High failure rates afflict many stages of this process, and even though millions of gametes are released by each colony, few new colonies form.<!--thousands of gametes or millions?--> The time from spawning to settling is usually two to three days, but can be up to two months.<ref name=Jones>{{cite book |author1=Jones, O.A. |author2=R. Endean. | year = 1973 | title = Biology and Geology of Coral Reefs | pages = 205–45
| publisher = Harcourt Brace Jovanovich | location = New York, USA | isbn = 0-12-389602-9}}</ref> The larva grows into a polyp and eventually becomes a coral head by asexual budding and growth.
===Asexual===
[[File:Orbicella annularis - calices.jpg|thumb|upright|Basal plates (calices) of ''Orbicella annularis'' showing multiplication by budding (small central plate) and division (large double plate)]]
[[File:AuloporaDevonianSilicaShale.jpg|thumb|upright|Tabulate coral ''[[Aulopora]]'' ([[Devonian]]) showing initial budding]]
Within a coral head, the genetically identical polyps reproduce [[asexual reproduction|asexually]], either by [[budding]] (gemmation) or by dividing, whether longitudinally or transversely.
Budding involves splitting a smaller polyp from an adult.<ref name=Barnes99 /> As the new polyp grows, it forms [[:Image:Coral polyp.jpg|its body parts]]. The distance between the new and adult polyps grows, and with it, the coenosarc (the common body of the colony). Budding can be intratentacular, from its oral discs, producing same-sized polyps within the ring of tentacles, or extratentacular, from its base, producing a smaller polyp.
Division forms two polyps that each become as large as the original. Longitudinal division begins when a polyp broadens and then divides its coelenteron (body), effectively splitting along its length. The mouth divides and new tentacles form. The two polyps thus created then generate their missing body parts and exoskeleton. Transversal division occurs when polyps and the exoskeleton divide transversally into two parts. This means one has the basal disc (bottom) and the other has the oral disc (top); the new polyps must separately generate the missing pieces.
Asexual reproduction offers the benefits of high reproductive rate, delaying senescence, and replacement of dead modules, as well as geographical distribution.<ref>{{cite book |title=Hawaiian Coral Reef Ecology |year=1998 |last=Gulko | first=David |publisher=Mutual Publishing |location=Honolulu, Hawaii |isbn=1-56647-221-0 |page=10}}</ref>
===Colony division===
Whole colonies can reproduce asexually, forming two colonies with the same genotype. The possible mechanisms include fission, bailout and fragmentation. Fission occurs in some corals, especially among the family [[Fungiidae]], where the colony splits into two or more colonies during early developmental stages. Bailout occurs when a single polyp abandons the colony and settles on a different substrate to create a new colony. Fragmentation involves individuals broken from the colony during storms or other disruptions. The separated individuals can start new colonies.<ref name="SheppardDavy2009">{{cite book |last1=Sheppard |first1=Charles R.C.|last2=Davy |first2=Simon K. |last3=Pilling |first3=Graham M. |title=The Biology of Coral Reefs |url=https://books.google.com/books?id=toIeBQAAQBAJ&pg=PT78 |date=25 June 2009|publisher=OUP Oxford|isbn=978-0-19-105734-2 |pages=78–81}}</ref>
==Reefs==
[[File:Coral reef locations.jpg|thumb|380px|Locations of coral reefs around the world]]
{{main article|Coral reef}}
{{see also|Coral reef fish|List of reefs}}
Many corals in the order [[Scleractinia]] are [[Hermatypic coral|hermatypic]], meaning that they are involved in building reefs. Most such corals obtain some of their energy from [[zooxanthellae]] in the genus ''Symbiodinium''. These are [[symbiosis|symbiotic]] photosynthetic [[dinoflagellate]]s which require sunlight; reef-forming corals are therefore found mainly in shallow water. They secrete calcium carbonate to form hard skeletons that become the framework of the reef. However, not all reef-building corals in shallow water contain zooxanthellae, and some deep water species, living at depths to which light cannot penetrate, form reefs but do not harbour the symbionts.<ref name=Schuhmacher>{{cite journal |author1=Schuhmacher, Helmut |author2=Zibrowius, Helmut |year=1985 |title=What is hermatypic? |journal=Coral Reefs |volume=4 |issue=1 |pages=1–9 |doi=10.1007/BF00302198 |bibcode=1985CorRe...4....1S}}</ref>
[[File:Hertshoon.jpg|thumb|left|[[Staghorn coral]] (''Acropora cervicornis'') is an important hermatypic coral from the Caribbean]]
There are various types of shallow-water coral reef, including fringing reefs, barrier reefs and atolls; most occur in tropical and subtropical seas. They are very slow-growing, adding perhaps one centimetre (0.4 in) in height each year. The [[Great Barrier Reef]] is thought to have been laid down about two million years ago. Over time, corals fragment and die, sand and rubble accumulates between the corals, and the shells of clams and other molluscs decay to form a gradually evolving calcium carbonate structure.<ref>{{cite encyclopedia|author=MSN Encarta |year=2006 |title=Great Barrier Reef |url=http://encarta.msn.com/encyclopedia_761575831/Great_Barrier_Reef.html |accessdate=April 25, 2015 |archiveurl=http://www.webcitation.org/5kwqDXqi5?url=http://encarta.msn.com/encyclopedia_761575831/Great_Barrier_Reef.html |archivedate=November 1, 2009 |deadurl=yes |df= }}</ref> Coral reefs are extremely diverse marine [[ecosystem]]s hosting over 4,000 species of fish, massive numbers of cnidarians, [[Mollusca|molluscs]], [[crustacean]]s, and many other animals.<ref name=Spalding>{{cite book |author1=Spalding, Mark |author2=Ravilious, Corinna |author3=Green, Edmund | year = 2001 | title = World Atlas of Coral Reefs | pages = 205–45 | publisher = University of California Press and UNEP/WCMC | location = Berkeley, CA | isbn = 0-520-23255-0}}</ref>
==Evolutionary history==
[[File:RugosaOrdovician.jpg|thumb|Solitary rugose coral (''Grewingkia'') in three views; Ordovician, southeastern Indiana]]
Although corals first appeared in the [[Cambrian]] period,<ref name=Pratt>{{cite book | last=Pratt | first=B.R. | author2=Spincer, B.R., R.A. Wood and A.Yu. Zhuravlev | title=Ecology of the Cambrian Radiation | year=2001 | url=ftp://gis.dipbsf.uninsubria.it/zoo/The%20Ecology%20of%20the%20Cambrian%20Radiation%20-%20Andrey%20Zhuravlev.pdf | accessdate=2007-04-06 | publisher=Columbia University Press | isbn=0-231-10613-0 | page=259 | chapter=12: Ecology and Evolution of Cambrian Reefs }}</ref> some {{Ma|542}}, [[fossil]]s are extremely rare until the [[Ordovician]] period, 100 million years later, when [[Rugosa|rugose]] and [[tabulate coral]]s became widespread. [[Paleozoic]] corals often contained numerous endobiotic symbionts.<ref name="VinnMotus2008">{{cite journal | doi=10.1666/07-056.1 | title=The earliest endosymbiotic mineralized tubeworms from the Silurian of Podolia, Ukraine | year=2008 | author=Vinn, O. | author2=Mõtus, M.-A. | journal=Journal of Paleontology | volume=82 | issue=2 | pages=409–14 | url=https://www.researchgate.net/publication/222089801_The_earliest_endosymbiotic_mineralized_tubeworms_from_the_Silurian_of_Podolia_Ukraine | accessdate=2014-06-11}}</ref><ref name="VinnMotus2012">{{cite journal | title=Diverse early endobiotic coral symbiont assemblage from the Katian (Late Ordovician) of Baltica | year=2012 | author=Vinn, O. | author2=Mõtus, M.-A. | journal=Palaeogeography, Palaeoclimatology, Palaeoecology | volume=321–322 | pages=137–41 |doi=10.1016/j.palaeo.2012.01.028 | url=https://www.researchgate.net/publication/255569552_Diverse_early_endobiotic_coral_symbiont_assemblage_from_the_Katian_%28Late_Ordovician%29_of_Baltica | accessdate=2014-06-11}}</ref>
Tabulate corals occur in [[limestone]]s and calcareous [[shale]]s of the Ordovician and [[Silurian]] periods, and often form low cushions or branching masses of [[calcite]] alongside rugose corals. Their numbers began to decline during the middle of the Silurian period, and they became extinct at the end of the [[Permian]] period, {{Ma|250}}.<ref>{{cite web|title=Introduction to the Tabulata|url=http://www.ucmp.berkeley.edu/cnidaria/tabulata.html|publisher=UCMP Berkeley|accessdate=25 April 2015}}</ref>
Rugose or horn corals became dominant by the middle of the Silurian period, and became extinct early in the [[Triassic]] period. The rugose corals existed in solitary and colonial forms, and were also composed of calcite.<ref>{{cite web|title=Introduction to the Rugosa|url=http://www.ucmp.berkeley.edu/cnidaria/rugosa.html|publisher=UCMP Berkeley|accessdate=25 April 2015}}</ref>
The [[scleractinia]]n corals filled the niche vacated by the extinct rugose and tabulate species. Their fossils may be found in small numbers in rocks from the Triassic period, and became common in the [[Jurassic]] and later periods.<ref>{{cite web|title=Evolutionary history |url=http://coral.aims.gov.au/info/evolution.jsp |website=AIMS |accessdate=25 April 2015}}</ref> Scleractinian skeletons are composed of a form of calcium carbonate known as [[aragonite]].<ref name=Ries>{{cite journal | author=Ries, J.B., Stanley, S.M., Hardie, L.A. | date=July 2006 | title=Scleractinian corals produce calcite, and grow more slowly, in artificial Cretaceous seawater | journal=Geology | volume=34 | issue =7 | pages=525–28 | doi=10.1130/G22600.1 |last2=Stanley |last3=Hardie}}</ref> Although they are geologically younger than the tabulate and rugose corals, the aragonite of their skeletons is less readily preserved, and their fossil record is accordingly less complete.
{{Coral fossil record timeline}}
At certain times in the geological past, corals were very abundant. Like modern corals, these ancestors built reefs, some of which ended as great structures in [[sedimentary rocks]]. Fossils of fellow reef-dwellers algae, sponges, and the remains of many [[Echinoderm|echinoids]], [[brachiopod]]s, [[bivalve]]s, [[gastropod]]s, and [[trilobite]]s appear along with coral fossils. This makes some corals useful [[index fossil]]s.<ref>{{cite web |last1=Alden |first1=Andrew |title=Index Fossils |url=http://geology.about.com/od/glossaryofgeology/g/Index-Fossils.htm |publisher=About education |accessdate=25 April 2015}}</ref> Coral fossils are not restricted to reef remnants, and many solitary fossils may be found elsewhere, such as ''Cyclocyathus'', which occurs in England's [[Gault clay]] formation.
==Status==
{{Main article|Environmental issues with coral reefs}}
===Threats===
[[File:Reef0484.jpg|thumb|upright|A healthy coral reef has a striking level of biodiversity in many forms of marine life.]]
Coral reefs are under stress around the world.<ref name="Coral reefs around the world">{{cite news |url=https://www.theguardian.com/environment/interactive/2009/sep/02/coral-world-interactive |title=Coral reefs around the world |publisher=[[Guardian.co.uk]] |date=2 September 2009}}</ref> In particular, coral mining, [[agricultural runoff|agricultural]] and [[urban runoff]], [[pollution]] (organic and inorganic), [[overfishing]], [[blast fishing]], disease, and the digging of [[canal]]s and access into islands and bays are localized threats to coral ecosystems. Broader threats are sea temperature rise, sea level rise and [[pH]] changes from [[ocean acidification]], all associated with [[greenhouse gas]] emissions.<ref name=cra10>{{cite web|title=Threats to Coral Reefs|url=http://www.coral.org/resources/about_coral_reefs/threats_to_coral_reefs|publisher=[[Coral Reef Alliance]]|year=2010|accessdate=5 December 2011|deadurl=yes|archiveurl=https://web.archive.org/web/20111201035325/http://www.coral.org/resources/about_coral_reefs/threats_to_coral_reefs|archivedate=1 December 2011|df=}}</ref> In 1998, 16% of the world's reefs died as a result of increased water temperature.<ref>[http://blogs.ei.columbia.edu/2011/06/13/losing-our-coral-reefs/ Losing Our Coral Reefs – Eco Matters – State of the Planet]. Blogs.ei.columbia.edu. Retrieved on 2011-11-01.</ref>
Approximately 10% of the world's coral reefs are dead.<ref name="Kleypas, J.A. 2006">{{Cite journal |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. |last6=Robbins |year=2006 |title=Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers: A guide for Future Research |publisher=[[National Science Foundation]], [[NOAA]], & [[United States Geological Survey]] |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=235–76 |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 human-related activities.<ref>{{cite book |last=Burke |first=Lauretta |title=Reefs at risk revisited |year=2011 |publisher=World Resources Institute |location=Washington, DC |isbn=978-1-56973-762-0 |page=38 |author2=Reytar, K. |author3=Spalding, M. |author4=Perry, A. }}</ref> The threat to reef health is particularly strong in [[Southeast Asia]], where 80% of reefs are [[endangered species|endangered]].<ref>{{cite web|last1=Bryant|first1=Dirk|last2=Burke|first2=Lauretta|last3=McManus|first3=John|last4=Spalding|first4=Mark|title=Reefs at Risk: A Map-Based Indicator of Threats to the World's Coral Reef|url=http://coralreef.noaa.gov/aboutcrcp/strategy/reprioritization/wgroups/resources/climate/resources/reefsatrisk.pdf|publisher=NOAA|accessdate=25 April 2015}}</ref> Over 50% of the world's [[coral reef]]s may be destroyed by 2030; as a result, most nations protect them through environmental laws.<ref name=Norlander>{{cite journal | author= Norlander | title= Coral crisis! Humans are killing off these bustling underwater cities. Can coral reefs be saved? (Life science: corals) | journal=Science World | date=8 December 2003 | url=http://www.thefreelibrary.com/Coral+crisis!+Humans+are+killing+off+these+bustling+underwater...-a0112022348}}</ref>
In the Caribbean and tropical Pacific, direct contact between ~40–70% of common seaweeds and coral causes bleaching and death to the coral via transfer of [[lipid]]-soluble [[metabolite]]s.<ref>{{cite journal |author=Rasher DB, Hay ME |title=Chemically rich seaweeds poison corals when not controlled by herbivores |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=107 |issue=21 |pages=9683–88 |date=May 2010 |pmid=20457927 |pmc=2906836 |doi=10.1073/pnas.0912095107|last2=Hay }}</ref> Seaweed and algae proliferate given adequate [[nutrients]] and limited grazing by [[herbivore]]s such as [[parrotfish]].
Water temperature changes of more than 1–2 °C (1.8–3.6 °F) or [[salinity]] changes can kill some species of coral. Under such environmental stresses, corals expel their [[Symbiodinium]]; without them coral tissues reveal the white of their skeletons, an event known as [[coral bleaching]].<ref name=Hoegh>{{cite journal | author=Hoegh-Guldberg, O. | title=Climate change, coral bleaching and the future of the world's coral reefs | journal=Marine and Freshwater Research | year=1999 | pages=839–66 | volume=50 | issue=8 | url=http://www.reef.edu.au/ohg/res-pic/HG%20papers/Hoegh-Guldberg%201999.pdf |format=PDF| doi=10.1071/MF99078 | authorlink=Ove Hoegh-Guldberg (biologist)}}</ref>
Submarine springs found along the coast of Mexico's [[Yucatán Peninsula]] produce water with a naturally low pH (relatively high acidity) providing conditions similar to those expected to become widespread as the oceans absorb carbon dioxide.<ref name=Stephens>{{cite web |last1=Stephens |first1=Tim |title=Submarine springs offer preview of ocean acidification effects on coral reefs |url=http://news.ucsc.edu/2011/11/coral-reefs.html |publisher=University of California Santa Cruz |date=28 November 2011 |accessdate=25 April 2015}}</ref> Surveys discovered multiple species of live coral that appeared to tolerate the acidity. The colonies were small and patchily distributed, and had not formed structurally complex reefs such as those that compose the nearby [[Mesoamerican Barrier Reef System]].<ref name=Stephens/>
===Protection===
{{Main article|Coral reef protection}}
[[Marine Protected Area|Marine Protected Areas (MPAs)]], [[Biosphere reserves]], [[marine park]]s, [[national monument]]s [[world heritage]] status, [[Fisheries management|fishery management]] and [[habitat (ecology)|habitat protection]] can protect reefs from anthropogenic damage.<ref>{{cite web |title=Phoenix Rising |publisher=National Geographic Magazine |date=January 2011 |accessdate=April 30, 2011
|url=http://ngm.nationalgeographic.com/2011/01/phoenix-islands/stone-text}}</ref>
Many governments now prohibit removal of coral from reefs, and inform coastal residents about reef protection and ecology. While local action such as habitat restoration and herbivore protection can reduce local damage, the longer-term threats of acidification, temperature change and sea-level rise remain a challenge.<ref name=cra10/>
To eliminate destruction of corals in their indigenous regions, projects have been started to grow corals in non-tropical countries.<ref>[http://www.ecodeco.nl/html/applications.htm EcoDeco EcologicalTechnology] {{webarchive|url=https://web.archive.org/web/20110307104000/http://www.ecodeco.nl/html/applications.htm |date=2011-03-07 }}. Ecodeco.nl. Retrieved on 2011-11-29.</ref><ref>[http://www.koraalwetenschap.nl/content/view/277/1/ KoralenKAS project] {{webarchive|url=https://web.archive.org/web/20120426021608/http://www.koraalwetenschap.nl/content/view/277/1/ |date=2012-04-26 }}. Koraalwetenschap.nl. Retrieved on 2011-11-29.</ref>
==Relation to humans==
Local economies near major coral reefs benefit from an abundance of fish and other marine creatures as a food source. Reefs also provide recreational [[scuba diving]] and [[snorkeling]] tourism. These activities can damage coral but international projects such as [[Green Fins]] that encourage dive and snorkel centres to follow a Code of Conduct have been proven to mitigate these risks.<ref>{{cite journal |last1=Hunt |first1=Chloe V. |last2=Harvey |first2=James J. |last3=Miller |first3=Anne |last4=Johnson |first4=Vivienne |last5=Phongsuwan |first5=Niphon |year=2013 |title=The Green Fins approach for monitoring and promoting environmentally sustainable scuba diving operations in South East Asia |journal=Ocean & Coastal Management |volume=78 |pages=35–44 |doi=10.1016/j.ocecoaman.2013.03.004}}</ref>
Live coral is highly sought after for [[aquarium|aquaria]]. Soft corals are easier to maintain in captivity than hard corals.<ref>{{cite web |url=http://aquadaily.com/2008/12/05/eight-great-soft-corals-for-new-reefkeepers/ |title=Eight great soft corals for new reefkeepers|accessdate=2009-01-02|date=2008-12-05|publisher=AquaDaily}}</ref>
===Jewelry===
[[File:6-Strand Necklace, Navajo (Native American), ca. 1920s, 71.57.1.jpg|thumb|upright=0.6|6-strand necklace, [[Navajo people|Navajo]] (Native American), ca. 1920s, [[Brooklyn Museum]]]]
{{main article|Coral (precious)}}
Corals' many colors give it appeal for necklaces and other [[jewelry]]. Intensely red coral is prized as a gemstone. Sometimes called fire coral, it is not the same as [[fire coral]]. Red coral is very rare because of [[overharvesting]].<ref>{{cite news |title= Coral makes a splash|first= Melissa|last= Magsaysay|url= http://articles.latimes.com/2009/jun/21/image/ig-coral21|newspaper= Los Angeles Times|date= June 21, 2009|accessdate=January 12, 2013}}</ref>
Always considered a precious mineral, "the Chinese have long associated red coral with auspiciousness and longevity because of its color and its resemblance to deer antlers (so by association, virtue, long life, and high rank".<ref>Welch, Patricia Bjaaland, ''Chinese Art: A Guide to Motifs and Visual Imagery''. Tokyo, Rutland and Singapore: Tuttle, 2008, p. 61</ref> It reached its height of popularity during the Manchu or Qing Dynasty (1644-1911) when it was almost exclusively reserved for the emperor's use either in the form of coral beads (often combined with pearls) for court jewelry or as decorative [[Penjing]] (decorative miniature mineral trees). Coral was known as ''shanhu'' in Chinese. The "early-modern 'coral network' [began in] the Mediterranean Sea [and found its way] to Qing China via the English [[East India Company]]".<ref>Lacey, Pippa, "The Coral Network: The trade of red coral to the Qing imperial court in the eighteenth century" in ''The Global Lives of Things'', ed. by Anne Gerritsen and Giorgio Aiello, London: Rutledge, 2016, p. 81</ref> There were strict rules regarding its use in a code established by the [[Qianlong Emperor]] in 1759.
===Medicine===
[[Image:ViennaDioscoridesCoral.jpg|thumb|left|Depiction of coral in the [[Juliana Anicia Codex]], a copy, written in [[Constantinople]] in 515 AD, of [[Dioscorides]]' 1st century AD [[Greek language|Greek]] work. The facing page states that coral can be used to treat ulcers.<ref>Folio 391, [[Juliana Anicia Codex]]</ref>]]
In medicine, chemical compounds from corals are used to treat cancer, AIDS and pain, and for other uses. Coral skeletons, e.g. ''[[Isididae]]'' are also used for [[bone graft]]ing in humans.<ref name="wiley">{{cite journal |url=http://www3.interscience.wiley.com/journal/112672000/abstract |title=Biomaterial structure in deep-sea bamboo coral (Anthozoa: Gorgonacea: Isididae) |journal=Materialwissenschaft und Werkstofftechnik|volume=37|issue=6|pages=552–57|publisher=www3.interscience.wiley.com|accessdate=2009-05-11|last=H. Ehrlich, P. Etnoyer, S. D. Litvinov|doi= 10.1002/mawe.200600036|year=2006|last2=Etnoyer|first2=P.|last3=Litvinov|first3=S. D.|last4=Olennikova|first4=M.M.
|last5=Domaschke|first5=H.|last6=Hanke|first6=T.|last7=Born|first7=R.|last8=Meissner|first8=H.|last9=Worch|first9=H.|display-authors=etal}}</ref>
Coral Calx, known as Praval Bhasma in [[Sanskrit]], is widely used in traditional system of [[Ayurveda|Indian medicine]] as a supplement in the treatment of a variety of bone metabolic disorders associated with calcium deficiency.<ref>{{cite journal |author=Reddy PN, Lakshmana M, Udupa UV |title=Effect of Praval bhasma (Coral calx), a natural source of rich calcium on bone mineralization in rats |journal=Pharmacological Research |volume=48 |issue=6 |pages=593–99 |date=December 2003 |pmid=14527824 |doi=10.1016/S1043-6618(03)00224-X|last2=Lakshmana |last3=Udupa }}</ref> In classical times ingestion of pulverized coral, which consists mainly of the weak base [[calcium carbonate]], was recommended for calming stomach ulcers by [[Galen]] and [[Dioscorides]].<ref>Pedanius Dioscorides – Der Wiener Dioskurides, Codex medicus Graecus 1 der Österreichischen Nationalbibliothek Graz: Akademische Druck- und Verlagsanstalt 1998 fol. 391 verso (Band 2), Kommentar S. 47 und 52. {{ISBN|3-201-01725-6}}</ref>
===Construction===
[[File:Syringoporid.jpg|thumb|Tabulate coral (a syringoporid); Boone limestone (Lower [[Carboniferous]]) near Hiwasse, Arkansas, scale bar is 2.0 cm.]]
Coral reefs in places such as the East African coast are used as a source of [[building material]].<ref name="Pouwels2002">{{cite book |last=Pouwels |first=Randall L.|title=Horn and Crescent: Cultural Change and Traditional Islam on the East African Coast, 800–1900 |url=https://books.google.com/books?id=iyw-_NMk0bgC&pg=PA26 |date=6 June 2002 |publisher=Cambridge University Press |isbn=978-0-521-52309-7 |page=26}}</ref> Ancient (fossil) coral limestone, notably including the [[Coral Rag Formation]] of the hills around [[Oxford]] (England), was once used as a building stone, and can be seen in some of the oldest buildings in that city including the Saxon tower of [[St Michael at the Northgate]], St. George's Tower of [[Oxford Castle]], and the mediaeval walls of the city.<ref>{{cite web |title=Strategic Stone Study: A Building Stone Atlas of Oxfordshire |url=https://www.bgs.ac.uk/downloads/start.cfm?id=1617 |publisher=English Heritage |accessdate=23 April 2015 |date=March 2011}}</ref>
===Climate research===
Annual growth bands in some corals, such as the [[deep sea]] [[bamboo coral]]s (''Isididae''), may be among the first signs of the effects of ocean acidification on marine life.<ref>{{cite web |url=http://www.noaanews.noaa.gov/stories2009/20090305_coral.html|title=National Oceanic and Atmospheric Administration – New Deep-Sea Coral Discovered on NOAA-Supported Mission |publisher=www.noaanews.noaa.gov |accessdate=2009-05-11}}</ref> The growth rings allow [[Geology|geologists]] to construct year-by-year chronologies, a form of [[incremental dating]], which underlie high-resolution records of past [[paleoclimatology|climatic]] and [[paleoecology|environmental]] changes using [[geochemistry|geochemical]] techniques.<ref name=Schrag>{{cite journal |author1=Schrag, D.P. |author2=Linsley, B.K. | title=Corals, chemistry, and climate | journal=Science | year=2002 | pages=277–78 | volume=296 | issue=8 | pmid=11951026 | doi= 10.1126/science.1071561}}</ref>
Certain species form communities called [[microatoll]]s, which are colonies whose top is dead and mostly above the water line, but whose perimeter is mostly submerged and alive. Average [[tide]] level limits their height. By analyzing the various growth morphologies, microatolls offer a low resolution record of sea level change. Fossilized microatolls can also be dated using [[Radiocarbon dating]]. Such methods can help to reconstruct [[Holocene]] [[sea level]]s.<ref name=Smithers>{{cite journal |last1=Smithers |first1=Scott G. |last2=Woodroffe |first2=Colin 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>
Increasing sea temperatures in tropical regions (~1 degree C) the last century have caused major coral bleaching, death, and therefore shrinking coral populations since although they are able to adapt and acclimate, it is uncertain if this evolutionary process will happen quickly enough to prevent major reduction of their numbers.<ref name="Hoegh-Guldberg">{{cite journal | author=Hoegh-Guldberg O. | title=Climate change, coral bleaching and the future of the world's coral reefs | journal=Marine and Freshwater Research | year=1999 | pages=839–99 | volume=50 | issue=8 | doi=10.1071/mf99078}}</ref>
Though coral have large sexually-reproducing populations, their evolution can be slowed by abundant [[asexual reproduction]].<ref name="Hughes et al.">{{cite journal |author1=Hughes, T. |author2=Baird, A. |author3=Bellwood, D. |author4=Card, M. |author5=Connolly, S. |author6=Folke, C. |author7=Grosberg, R. |author8=Hoegh-Guldberg, O. |author9=Jackson, J. |author10=Klepas, J. |author11=Lough, J. |author12=Marshall, P. |author13=Nystrom, M. |author14=Palumbi, S. |authorlink14=Stephen Palumbi |author15=Pandolfi, J. |author16=Rosen, B. |author17=and Roughgarden, J. | title=Climate change, human impacts, and the resilience of coral reefs | journal=Science | year=2003 | pages=929–33 | volume=301 | issue=5635 | doi=10.1126/science.1085046| pmid=12920289 }}</ref> [[Gene flow]] is variable among coral species.<ref name="Hughes et al."/> According to the [[biogeography]] of coral species gene flow cannot be counted on as a dependable source of adaptation as they are very stationary organisms. Also, coral longevity might factor into their adaptivity.<ref name="Hughes et al."/>
However, [[adaptation to climate change]] has been demonstrated in many cases. These are usually due to a shift in coral and zooxanthellae [[genotype]]s. These shifts in [[allele frequency]] have progressed toward more tolerant types of zooxanthellae.<ref name=Parmesan>{{cite journal | author=Parmesan, C. | title=Ecological and evolutionary responses to recent climate change | journal= Annual Review of Ecology, Evolution, and Systematics | year=2006 | pages=637–69 | volume=37 | doi=10.1146/annurev.ecolsys.37.091305.110100}}</ref> Scientists found that a certain [[scleractinia]]n zooxanthella is becoming more common where sea temperature is high.<ref name=Baker>{{cite journal | author=Baker, A. | title= Corals' adaptive response to climate change |journal=Nature | year=2004 | page=741 | volume=430 | issue= 7001 | doi=10.1038/430741a}}</ref><ref name="Donner et al.">{{cite journal | author= Donner, S., Skirving, W., Little, C., Oppenheimer, M., and Hoegh-Guldenberg | title= Global assessment of coral bleaching and required rates of adaptation under climate change | journal=Global Change Biology | year=2005 | pages=2251–65 | volume=11 | issue= 12 | doi=10.1111/j.1365-2486.2005.01073.x}}</ref> Symbionts able to tolerate warmer water seem to photosynthesise more slowly, implying an evolutionary trade-off.<ref name="Donner et al."/>
In the Gulf of Mexico, where sea temperatures are rising, cold-sensitive [[Staghorn coral|staghorn]] and [[elkhorn coral]] have shifted in location.<ref name="Parmesan"/>
Not only have the symbionts and specific species been shown to shift, but there seems to be a certain growth rate favorable to selection. Slower-growing but more heat-tolerant corals have become more common.<ref name="Baskett et al.">{{cite journal |author1=Baskett, M. |author2=Gaines, S. |author3=Nisbet, R. |last-author-amp=yes | title= Symbiont diversity may help coral reefs survive moderate climate change | journal=Ecological Applications | year=2009 | pages=3–17 | volume=19 | issue= 1 | doi=10.1890/08-0139.1| pmid= 19323170 }}</ref> The changes in temperature and acclimation are complex. Some reefs in current shadows represent a refugium location that will help them adjust to the disparity in the environment even if eventually the temperatures may rise more quickly there than in other locations.<ref name="McClanahan et al.">{{cite journal |author1=McClanahan, T. |author2=Ateweberhan, M. |author3=Muhando, C. |author4=Maina, J. |author5= Mohammed, M. |last-author-amp=yes | title= Effects of Climate and Seawater Temperature Variation on Coral Bleaching and Morality | journal=Ecological Monographs | year=2007 | pages=503–25 | volume=77 | issue= 4 | doi=10.1890/06-1182.1}}</ref> This [[vicariance|separation of populations]] by climatic barriers causes a [[realized niche]] to shrink greatly in comparison to the old [[fundamental niche]].
==== Geochemistry ====
Corals are shallow, colonial organisms that integrate [[δ18O|δ<sup>18</sup>O]] and trace elements into their skeletal [[aragonite]] ([[Polymorphism (materials science)|polymorph]] of [[calcite]]) crystalline structures, as they grow. Geochemistry anomalies within the crystalline structures of corals represent functions of temperature, salinity and oxygen isotopic composition. Such geochemical analysis can help with climate modeling.<ref>{{cite journal|last1=Kilbourne|first1=K. Halimeda|last2=Quinn|first2=Terrence M.|last3=Taylor|first3=Frederick W.|last4=Delcroix|first4=Thierry|last5=Gouriou|first5=Yves |year=2004 |title=El Niño-Southern Oscillation-related salinity variations recorded in the skeletal geochemistry of a ''Porites'' coral from Espiritu Santo, Vanuatu |journal=Paleoceanography |volume=19 |issue=4 |pages=PA4002 |doi=10.1029/2004PA001033 |bibcode=2004PalOc..19.4002K}}</ref>
===== Strontium/calcium ratio anomaly =====
Time can be attributed to coral geochemistry anomalies by correlating [[strontium]]/[[calcium]] minimums with [[sea surface temperature|sea surface temperature (SST)]] maximums to data collected from [http://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/Nino34/ NINO 3.4 SSTA].<ref name="Ren, L. 2002">{{cite journal|last1=Ren|first1=Lei|last2=Linsley|first2=Braddock K.|last3=Wellington|first3=Gerard M.|last4=Schrag|first4=Daniel P.|last5=Hoegh-guldberg|first5=Ove |year=2003 |title=Deconvolving the δ<sup>18</sup>O seawater component from subseasonal coral δ<sup>18</sup>O and Sr/Ca at Rarotonga in the southwestern subtropical Pacific for the period 1726 to 1997 |journal=Geochimica et Cosmochimica Acta |volume=67 |issue=9 |pages=1609–21 |doi=10.1016/S0016-7037(02)00917-1 |bibcode=2003GeCoA..67.1609R}}</ref>
<!-- [[WP:NFCC]] violation: [[File:Linsley2006 figure1.png|thumb|The position of the [[South Pacific convergence zone]] as a function of precipitation and salinity]] -->
===== Oxygen isotope anomaly =====
The comparison of coral strontium/calcium minimums with sea surface temperature maximums, data recorded from [http://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/Nino34/ NINO 3.4 SSTA], time can be correlated to coral strontium/calcium and [[Δ18O|δ<sup>18</sup>O]] variations. To confirm accuracy of the annual relationship between Sr/Ca and [[Δ18O|δ<sup>18</sup>O]] variations, a perceptible association to annual coral growth rings confirms the age conversion. [[Geochronology]] is established by the blending of Sr/Ca data, growth rings, and [[Stable isotope ratio|stable isotope]] data. [[El Nino-Southern Oscillation|El Nino-Southern Oscillation (ENSO)]] is directly related to climate fluctuations that influence coral [[Δ18O|δ<sup>18</sup>O]] ratio from local salinity variations associated with the position of the [[South Pacific convergence zone|South Pacific convergence zone (SPCZ)]] and can be used for [[El Niño Southern Oscillation|ENSO]] modeling.<ref name="Ren, L. 2002"/>
===== Sea surface temperature and sea surface salinity =====
[[File:Global Sea Surface Temperature - GPN-2003-00032.jpg|thumb|Global sea surface temperature (SST)]]
The global moisture budget is primarily being influenced by tropical sea surface temperatures from the position of the [[Intertropical Convergence Zone]] (ITCZ).<ref>{{cite journal|last1=Wu|first1=Henry C.|last2=Linsley|first2=Braddock K.|last3=Dassié|first3=Emilie P.|last4=Schiraldi|first4=Benedetto|last5=deMenocal|first5=Peter B. |year=2013 |title=Oceanographic variability in the South Pacific Convergence Zone region over the last 210 years from multi-site coral Sr/Ca records |journal=Geochemistry, Geophysics, Geosystems |volume=14 |issue=5 |pages=1435–53 |doi=10.1029/2012GC004293}}</ref> The [[Southern Hemisphere]] has a unique meteorological feature positioned in the southwestern Pacific Basin called the [[South Pacific convergence zone|South Pacific Convergence Zone (SPCZ)]], which contains a perennial position within the Southern Hemisphere. During [[El Niño Southern Oscillation|ENSO]] warm periods, the [[South Pacific convergence zone|SPCZ]] reverses orientation extending from the equator down south through [[Solomon Islands]], [[Vanuatu]], [[Fiji]] and towards the French [[Polynesian islands|Polynesian Islands]]; and due east towards [[South America]] affecting geochemistry of corals in tropical regions.<ref>{{cite journal|last1=Kiladis|first1=George N.|last2=von Storch|first2=Hans|last3=van Loon|first3=Harry |year=1989 |title=Origin of the South Pacific Convergence Zone |journal=Journal of Climate |volume=2 |issue=10 |pages=1185–95 |doi=10.1175/1520-0442(1989)002<1185:OOTSPC>2.0.CO;2}}</ref>
Geochemical analysis of skeletal coral can be linked to sea surface salinity (SSS) and [[sea surface temperature]] (SST), from [http://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/Nino34/ El Nino 3.4 SSTA] data, of tropical oceans to seawater [[Δ18O|δ<sup>18</sup>O]] ratio anomalies from corals. [[El Niño Southern Oscillation|ENSO]] phenomenon can be related to variations in sea surface salinity (SSS) and [[sea surface temperature|sea surface temperature (SST)]] that can help model tropical climate activities.<ref name="Lukas, R. 1991">{{cite journal|last1=Lukas|first1=Roger|last2=Lindstrom|first2=Eric |year=1991 |title=The mixed layer of the western equatorial Pacific Ocean|journal=Journal of Geophysical Research|volume=96 |issue=S1 |pages=3343–58 |doi=10.1029/90JC01951 |bibcode=1991JGR....96.3343L}}</ref>
===== Limited climate research on current species =====
[[File:Porites lutea.jpg|thumb|Genus: ''Porites lutea'']]
Climate research on live coral species is limited to a few studied species. Studying ''[[Porites]]'' coral provides a stable foundation for geochemical interpretations that is much simpler to physically extract data in comparison to ''[[Platygyra]]'' species where the complexity of ''[[Platygyra]]'' species skeletal structure creates difficulty when physically sampled, which happens to be one of the only multidecadal living coral records used for coral [[paleoclimate]] modeling.<ref name="Lukas, R. 1991"/>
===Aquaria===
{{main article|Reef aquarium}}
[[File:Zoanthus-dragon-eye.jpg|right|thumb|This dragon-eye zoanthid is a popular source of color in reef tanks]]
The saltwater fishkeeping hobby has increasingly expanded, over recent years, to include [[reef tank]]s, fish tanks that include large amounts of [[live rock]] on which coral is allowed to grow and spread.<ref>[http://www.advancedaquarist.com/2011/1/corals Aquarium Corals: Collection and Aquarium Husbandry of Northeast Pacific Non-Photosynthetic Cnidaria]. Advancedaquarist.com (2011-01-14). Retrieved on 2016-06-13.</ref> These tanks are either kept in a natural-like state, with algae (sometimes in the form of an [[algae scrubber]]) and a deep sand bed providing filtration,<ref>[http://reefkeeping.com/issues/2008-10/newbie/index.php Reefkeeping 101 – Various Nutrient Control Methods]. Reefkeeping.com. Retrieved on 2016-06-13.</ref> or as "show tanks", with the rock kept largely bare of the algae and [[microfauna]] that would normally populate it,<ref>[http://saltaquarium.about.com/od/aquariummaintenancecare/a/sandlrcleaning.htm Aquarium Substrate & Live Rock Clean Up Tips]. Saltaquarium.about.com. Retrieved on 2016-06-13.</ref> in order to appear neat and clean.
The most popular kind of coral kept is [[soft coral]], especially [[zoanthid]]s and mushroom corals, which are especially easy to grow and propagate in a wide variety of conditions, because they originate in enclosed parts of reefs where water conditions vary and lighting may be less reliable and direct.<ref>[http://marinebio.org/oceans/coral-reefs.asp Coral Reefs]. Marinebio.org. Retrieved on 2016-06-13.</ref> More serious fishkeepers may keep small polyp [[stony coral]], which is from open, brightly lit reef conditions and therefore much more demanding, while large polyp stony coral is a sort of compromise between the two.
===Aquaculture===
{{main article|Aquaculture of coral}}
[[Coral aquaculture]], also known as ''coral farming'' or ''coral gardening'', is the cultivation of corals for commercial purposes or coral reef restoration. Aquaculture is showing promise as a potentially effective tool for restoring [[coral reef]]s, 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 = 162–66 | doi=10.1016/j.jembe.2011.01.005| last2 = Izhaki | last3 = Rinkevich }}</ref><ref name="Pomeroy">{{cite journal |last1=Pomeroy |first1=Robert S. |last2=Parks |first2=John E. |last3=Balboa |first3=Cristina M. |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=111–30 |doi=10.1016/j.marpol.2004.09.001}}</ref><ref name="Rinkevich">{{cite journal|author=Rinkevich B |year=2008 |title=Management of coral reefs: We have gone wrong when neglecting active reef restoration |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 |dead-url=yes |archive-date=2013-05-23 |format=PDF |journal=Marine pollution bulletin |volume=56 |issue=11 |pages=1821–24 |doi=10.1016/j.marpolbul.2008.08.014 |pmid=18829052 }}</ref> The process bypasses the early growth stages of corals when they are most at risk of dying. Coral fragments known as "seeds" are grown in nurseries then replanted on the reef.<ref name="Ferse">{{cite journal |last1=Ferse |first1=Sebastian C.A. |year=2010|title=Poor Performance of Corals Transplanted onto Substrates of Short Durability |journal=Restoration Ecology |volume=18 |issue=4 |pages=399–407 |doi=10.1111/j.1526-100X.2010.00682.x}}</ref> Coral is farmed by coral farmers who live locally to the reefs and farm for reef [[Conservation movement|conservation]] or for income. It is also farmed by scientists for research, by businesses for the supply of the live and ornamental coral trade and by private [[aquarium]] hobbyists.
==Gallery==
''Further images: [[commons:Category:Coral reefs]] and [[commons:Category:Corals]]''
<gallery mode=packed>>
File:Mushroom Coral (Fungia) Top Macro 91.JPG| ''[[Fungia]]'' sp. skeleton
File:Eusmilia fastigiata large.jpg|Polyps of ''[[Eusmilia fastigiata]]''
File:Dendrogyra cylindrus (pillar coral) (San Salvador Island, Bahamas) 1 (15513345363).jpg|[[Pillar coral]], ''Dendrogyra cylindricus''
File:Brain coral.jpg|[[Brain coral]], ''[[Diploria labyrinthiformis]]''
File:Brain coral spawning.jpg|Brain coral spawning
File:Stony coral spawning 3.jpg|Brain coral releasing eggs
File:EilatFringingReef.jpg|Fringing [[coral reef]] off the coast of [[Eilat]], [[Israel]].
</gallery>
==References==
{{reflist|28em}}
==Sources==
* {{cite book|author1=Allen, G.R |author2=R. Steene | title=Indo-Pacific Coral Reef Field Guide | publisher = | date=1994 | isbn=981-00-5687-7}}
* {{cite book| author=Calfo, Anthony | title=Book of Coral Propagation | publisher= | date= | isbn=0-9802365-0-9}}
* {{cite book|author1=Colin, P.L. |author2=C. Arneson | title=Tropical Pacific Invertebrates
| publisher = | date=1995 | isbn=0-9645625-0-2}}
* {{cite book| author=Fagerstrom, J.A. | title=The Evolution of Reef Communities | publisher = | date=1987 | isbn=0-471-81528-4}}
* {{cite book| author=Gosliner, T., D. Behrens & G. Williams | title=Coral Reef Animals of the Indo-Pacific, Animals Life from Africa to Hawai'i (invertebrates)| publisher = | date=1996 | isbn=0-930118-21-9}}
* {{cite book| author=Nybakken, J.W. | title=Marine Biology, An Ecological Approach | publisher = | date=2004 | isbn=0-8053-4582-5}}
* {{cite book| author=Redhill, Surrey | title=Corals of the World: Biology and Field Guide | publisher = | date= }}
* {{cite book|author1=Segaloff, Nat |author2=Paul Erickson | title=A Reef Comes to Life. Creating an Undersea Exhibit | publisher = | date=1991 | isbn=0-531-10994-1}}
* {{cite book |last1=Sheppard |first1=Charles R.C.|last2=Davy |first2=Simon K. |last3=Pilling |first3=Graham M. |title=The Biology of Coral Reefs |url=https://books.google.com/books?id=toIeBQAAQBAJ&pg=PT78 |date=25 June 2009 |publisher=OUP Oxford|isbn=978-0-19-105734-2}}
* {{cite book| author=Veron, J.E.N. | title=Corals of Australia and the Indo-Pacific | publisher = | date=1993 | isbn=0-8248-1504-1}}
* {{cite book| author=Wells, Susan | title=Coral Reefs of the World | publisher= | date= }}
==External links==
{{wikispecies|Anthozoa|Coral}}
{{Commons category multi|Coral|Anthozoa}}
* [http://ocean.si.edu/ocean-life-ecosystems/coral-reefs Coral Reefs] The Ocean Portal by the [[Smithsonian Institution]]
* [[NOAA]] CoRIS – [http://www.coris.noaa.gov/about/ Coral Reef Biology]
* [[NOAA]] Ocean Service Education – [http://www.oceanservice.noaa.gov/education/kits/corals/welcome.html Corals]
* {{cite web|title= Coral Factsheet |url= http://waittinstitute.org/coral/ |accessdate= 2017-02-04 |publisher = Waitt Institute }}
* {{cite web|title= What is a coral? |url= http://www.stanford.edu/group/microdocs/whatisacoral.html |accessdate= 2017-02-04|publisher= Stanford microdocs project}}
{{good article}}
{{Corals}}
{{Living things in culture}}
[[Category:Anthozoa]]
[[Category:Coral reefs]]' |
