Editing Coral (section)

===Intracellular symbionts===
Many corals, as well as other [[cnidaria]]n groups such as [[sea anemone]]s form a [[symbiotic]] relationship with a class of [[dinoflagellate]] [[algae]], [[zooxanthellae]] of the genus ''[[Symbiodinium]]'', which can form as much as 30% of the tissue of a polyp.<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}}</ref>{{rp|23–24}} Typically, each polyp harbors one species of alga, and coral species show a preference for ''[[Symbiodinium]]''.<ref>{{cite journal|last1=Yuyama|first1=Ikuko|title=Comparing the Effects of Symbiotic Algae (Symbiodinium) Clades C1 and D on Early Growth Stages of Acropora tenuis|journal=PLOS ONE|date=2014|volume=9|issue=6|pages=e98999|doi=10.1371/journal.pone.0098999|pmid=24914677|pmc=4051649|bibcode=2014PLoSO...998999Y|doi-access=free}}</ref> Young corals are not born with zooxanthellae, but acquire the algae from the surrounding environment, including the water column and local sediment.<ref>{{cite journal|last1=Yamashita|first1=Hiroshi|title=Establishment of Coral–Algal Symbiosis Requires Attraction and Selection|journal=PLOS ONE|date=2014|volume=9|issue=5|pages=e97003|doi=10.1371/journal.pone.0097003|pmid=24824794|pmc=4019531|bibcode=2014PLoSO...997003Y|doi-access=free}}</ref> The main benefit of the zooxanthellae is their ability to photosynthesize which supplies corals with the products of photosynthesis, including glucose, glycerol, also amino acids, which the corals can use for energy.<ref>{{cite web|title=Zooxanthellae...What's That?|url=https://oceanservice.noaa.gov/education/kits/corals/coral02_zooxanthellae.html|website=NOAA Ocean Service Education|publisher=National Oceanic and Atmospheric Administration|access-date=1 December 2017|archive-date=13 April 2020|archive-url=https://web.archive.org/web/20200413062742/https://oceanservice.noaa.gov/education/kits/corals/coral02_zooxanthellae.html|url-status=dead}}</ref> Zooxanthellae also benefit corals by aiding in [[calcification]], for the coral skeleton, and waste removal.<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 |access-date=2006-03-31 |archive-date=2020-05-11 |archive-url=https://web.archive.org/web/20200511062206/http://biophysics.sbg.ac.at/png/png3.htm |url-status=dead }}</ref><ref>{{cite book|last1=van de Plaasche|first1=Orson|title=Sea-level research: a manual for the collection and evaluation of data|date=1986|publisher=Geo Books|location=Norwich, UK|isbn=978-94-010-8370-6|page=196}}</ref> In addition to the soft tissue, [[microbiome]]s are also found in the coral's mucus and (in stony corals) the skeleton, with the latter showing the greatest microbial richness.<ref>{{Cite web|url=https://www.psu.edu/news/research/story/corals-and-their-microbiomes-evolved-together/|title=Corals and their microbiomes evolved together &#124; Penn State University|website=psu.edu}}</ref>

The zooxanthellae benefit from a safe place to live and consume the polyp's [[carbon dioxide]], phosphate and nitrogenous waste. Stressed corals will eject their zooxanthellae, a process that is becoming increasingly common due to strain placed on coral by rising ocean temperatures. Mass ejections are known as [[coral bleaching]] because the algae contribute to coral coloration; some 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 and if the stress subsides 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 | s2cid=7765487 | access-date=2006-03-30 | archive-url=https://web.archive.org/web/20060225043356/http://www.biolbull.org/cgi/content/full/201/3/360 | archive-date=2006-02-25 | url-status=dead }}</ref> Zooxanthellae are located within the coral cytoplasm and due to the algae's photosynthetic activity the internal pH of the coral can be raised; this behavior indicates that the zooxanthellae are responsible to some extent for the metabolism of their host corals.<ref>{{cite journal|last1=Brownlee|first1=Colin|title=pH regulation in symbiotic anemones and corals: A delicate balancing act|journal=Proceedings of the National Academy of Sciences of the United States of America|date=2009|volume=106|issue=39|pages=16541–16542|doi=10.1073/pnas.0909140106|pmid=19805333|pmc=2757837|bibcode=2009PNAS..10616541B|doi-access=free}}</ref> Stony Coral Tissue Loss Disease has been associated with the breakdown of host-zooxanthellae physiology.<ref>Landsberg et al., "Stony Coral Tissue Loss Disease in Florida Is Associated With Disruption of Host–Zooxanthellae Physiology".</ref> Moreover, Vibrio bacterium are known to have virulence traits used for host coral tissue damage and photoinhibition of algal symbionts.<ref>de O Santos et al., "Genomic and Proteomic Analyses of the Coral Pathogen Vibrio Coralliilyticus Reveal a Diverse Virulence Repertoire".</ref> Therefore, both coral and their symbiotic microorganisms could have evolved to harbour traits resistant to disease and transmission.