Coral bleaching#Artificial assistance

File:Coral Bleaching.jpg

File:Climate change threats to coral reefs.png will affect coral reef ecosystems, through sea level rise, changes to the frequency and intensity of tropical storms, and altered ocean circulation patterns. When combined, all of these impacts dramatically alter ecosystem function, as well as the goods and services coral reef ecosystems provide.{{Cite web |last=US Department of Commerce |first=National Oceanic and Atmospheric Administration |title=How does climate change affect coral reefs? |url=https://oceanservice.noaa.gov/facts/coralreef-climate.html |access-date=2024-02-19 |website=oceanservice.noaa.gov |language=EN-US}} ]]

File:Zooxanthellae.jpg, the microscopic algae that lives inside coral, gives it colour and provides it with food through photosynthesis]]

The corals that form the great reef ecosystems of tropical seas depend upon a symbiotic relationship with algae-like single-celled flagellate protozoa called zooxanthellae that live within their tissues and give the coral its coloration. The zooxanthellae provide the coral with nutrients through photosynthesis, a crucial factor in the clear and nutrient-poor tropical waters. In exchange, the coral provides the zooxanthellae with the carbon dioxide and ammonium needed for photosynthesis. Negative environmental conditions, such as abnormally warm or cool temperatures, high light, and even some microbial diseases, can lead to the breakdown of the coral/zooxanthellae symbiosis.{{Cite book |editor-last1=Dubinzk |editor-first1=Z. |editor-last2=Stambler |editor-first2=N. |last=Lesser |first=M.P. |title=Coral Reefs: An Ecosystem in Transition |pages=405–419 |date=2010 |publisher=Springer |location=Dordrecht |isbn=978-94-007-0114-4 |doi=10.1007/978-94-007-0114-4_23 |chapter=Coral Bleaching: Causes and Mechanisms}} To ensure short-term survival, the coral-polyp then consumes or expels the zooxanthellae. This leads to a lighter or completely white appearance, hence the term "bleached".{{Cite journal |year=1999 |title=Climate change, coral bleaching and the future of the world's coral reefs |journal=Marine and Freshwater Research |volume=50 |issue=8 |pages=839–66 |doi=10.1071/MF99078 |last1=Hoegh-Guldberg |first1=Ove |author-link=Ove Hoegh-Guldberg (biologist) |doi-access=free}} Under mild stress conditions, some corals may appear bright blue, pink, purple, or yellow instead of white, due to the continued or increased presence of the coral cells' intrinsic pigment molecules, a phenomenon known as "colourful bleaching". As the zooxanthellae provide up to 90 percent of the coral's energy needs through products of photosynthesis, after expelling, the coral may begin to starve.

Coral can survive short-term disturbances, but if the conditions that lead to the expulsion of the zooxanthellae persist, the coral's chances of survival diminish. In order to recover from bleaching, the zooxanthellae have to re-enter the tissues of the coral polyps and restart photosynthesis to sustain the coral as a whole and the ecosystem that depends on it.{{Cite journal |vauthors=Nir O, Gruber DF, Shemesh E, Glasser E, Tchernov D |title=Seasonal mesophotic coral bleaching of Stylophora pistillata in the Northern Red Sea |journal=PLOS ONE |volume=9 |issue=1 |pages=e84968 |date=15 January 2014 |pmid=24454772 |pmc=3893136 |doi=10.1371/journal.pone.0084968 |bibcode=2014PLoSO...984968N |doi-access=free }}

If the coral polyps die of starvation after bleaching, they will decay. The hard coral species will then leave behind their calcium carbonate skeletons, which will be taken over by algae, effectively blocking coral regrowth. Eventually, the coral skeletons will erode, causing the reef structure to collapse.{{Citation needed|date=May 2021}}

File:CoralBleaching.jpg

Coral bleaching may be caused by a number of factors. While localized triggers lead to localized bleaching, the large-scale coral bleaching events of recent years have been triggered by global warming. Under the increased carbon dioxide concentration expected in the 21st century, corals are expected to become increasingly rare on reef systems.{{Cite journal |vauthors=Hoegh-Guldberg O, Mumby PJ, Hooten AJ, Steneck RS, Greenfield P, Gomez E, Harvell CD, Sale PF, Edwards AJ, Caldeira K, Knowlton N, Eakin CM, Iglesias-Prieto R, Muthiga N, Bradbury RH, Dubi A, Hatziolos ME |display-authors=6 |title=Coral reefs under rapid climate change and ocean acidification |journal=Science |volume=318 |issue=5857 |pages=1737–42 |date=December 2007 |pmid=18079392 |doi=10.1126/science.1152509 |bibcode=2007Sci...318.1737H |citeseerx=10.1.1.702.1733 |s2cid=12607336 }} Coral reefs located in warm, shallow water with low water flow have been more affected than reefs located in areas with higher water flow.{{Cite journal |last1=Baker |first1=Andrew |last2=Glynn |first2=Peter |last3=Riegl |first3=Bernhard |name-list-style=vanc |year=2008 |title=Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook |journal=Estuarine, Coastal and Shelf Science |volume=80 |issue=4 |pages=435–471 |bibcode=2008ECSS...80..435B |doi=10.1016/j.ecss.2008.09.003}} Marine heatwaves caused by the El Nino Southern Oscillation have been found to be one of the main causes of widespread coral bleaching and consequent coral mortality.{{Cite journal |last1=De |first1=Kalyan |last2=Nanajkar |first2=Mandar |last3=Mote |first3=Sambhaji |last4=Ingole |first4=Baban |date=2023-01-01 |title=Reef on the edge: resilience failure of marginal patch coral reefs in Eastern Arabian Sea under recurrent coral bleaching, coral diseases, and local stressors |url=https://doi.org/10.1007/s11356-022-22651-3 |journal=Environmental Science and Pollution Research |language=en |volume=30 |issue=3 |pages=7288–7302 |doi=10.1007/s11356-022-22651-3 |pmid=36031676 |bibcode=2023ESPR...30.7288D |issn=1614-7499}}

File:Colorful Coral Bleaching.jpg

File:EL18p-Réunion.jpg

• increased water temperature (marine heatwaves, most commonly due to global warming), or reduced water temperatures{{Cite press release |title=Reef 'at risk in climate change' |publisher=The University of Queensland |date=6 April 2007 |url=https://www.uq.edu.au/news/article/2007/04/reef-risk-climate-change |access-date=2 August 2016 |archive-date=13 September 2016 |archive-url=https://web.archive.org/web/20160913172127/https://www.uq.edu.au/news/article/2007/04/reef-risk-climate-change |url-status=live }}Anthony, K. 2007; Berkelmans{{Cite journal |vauthors=Saxby T, Dennison WC, Hoegh-Guldberg O |title=Photosynthetic responses of the coral Montipora digitata to cold temperature stress |doi=10.3354/meps248085 |journal=Marine Ecology Progress Series |volume=248 |pages=85–97 |year=2003 |bibcode=2003MEPS..248...85S |doi-access=free }}{{Cite journal |vauthors=Marimuthu N, Jerald Wilson J, Vinithkumar NV, Kirubagaran R |title=Coral reef recovery status in south Andaman Islands after the bleaching event 2010 |journal=Journal of Ocean University of China |date=9 November 2012 |volume=12 |issue=1 |pages=91–96 |doi=10.1007/s11802-013-2014-2 |bibcode=2013JOUC...12...91M |s2cid=89531419 }}
• increased solar irradiance (photosynthetically active radiation and ultraviolet light)
• increased sedimentation (due to silt runoff){{Cite journal |vauthors=Rogers CS | title=Responses of coral reefs and reef organisms to sedimentation |journal=Marine Ecology Progress Series |volume=62 |year=1990 |pages=185–202 |doi=10.3354/meps062185 |bibcode=1990MEPS...62..185R |doi-access=free }}
• bacterial infections{{Cite journal |vauthors=Kushmaro A, Rosenberg E, Fine M, Loya Y |title=Bleaching of the coral Oculina patagonica by Vibrio AK-1 |journal=Marine Ecology Progress Series |volume=147 |year=1997 |pages=159–65 |doi=10.3354/meps147159 |bibcode=1997MEPS..147..159K |doi-access=free }}
• changes in salinity{{Cite journal |last1=Hoegh-Guldberg |first1=Ove |author-link=Ove Hoegh-Guldberg (biologist) |last2=Smith |first2=G.Jason |name-list-style=vanc |title=The effect of sudden changes in temperature, light and salinity on the population density and export of zooxanthellae from the reef corals Stylophora pistillata Esper and Seriatopora hystrix Dana |journal=Journal of Experimental Marine Biology and Ecology |volume=129 |issue=3 |year=1989 |pages=279–303 |doi=10.1016/0022-0981(89)90109-3 |bibcode=1989JEMBE.129..279H }}
• herbicides{{Cite journal |vauthors=Jones RJ, Muller J, Haynes D, Schreiber U |title=Effects of herbicides diuron and atrazine on corals of the Great Barrier Reef, Australia |journal=Marine Ecology Progress Series |volume=251 |year=2003 |pages=153–167 |doi=10.3354/meps251153 |bibcode=2003MEPS..251..153J |doi-access=free }}
• extreme low tide and exposure{{Cite journal |vauthors=Anthony KR, Kerswell AP |title=Coral mortality following extreme low tides and high solar radiation |journal=Marine Biology |volume=151 |issue=5 |year=2007 |pages=1623–31 |doi=10.1007/s00227-006-0573-0 |bibcode=2007MarBi.151.1623A |s2cid=84328751 }}
• cyanide fishing{{Cite journal |last1=Jones |first1=Ross J. |last2=Hoegh-Guldberg |first2=Ove |author-link2=Ove Hoegh-Guldberg (biologist) |name-list-style=vanc |title=Effects of cyanide on coral photosynthesis:implications for identifying the cause of coral bleaching and for assessing the environmental effects of cyanide fishing |journal=Marine Ecology Progress Series |volume=177 |year=1999 |pages=83–91 |doi=10.3354/meps177083 |bibcode=1999MEPS..177...83J |doi-access=free }}
• elevated sea levels due to global warming (Watson){{clarify|date=August 2016}}
• mineral dust from African dust storms caused by drought{{Cite web |title=Coral Mortality and African Dust |url=http://coastal.er.usgs.gov/african_dust/ |url-status=dead |archive-url=https://web.archive.org/web/20120502091350/http://coastal.er.usgs.gov/african_dust/ |archive-date=2 May 2012 |access-date=10 June 2007 |website=U. S. Geological Survey}}
• pollutants such as oxybenzone, butylparaben, octyl methoxycinnamate, or enzacamene: four common sunscreen ingredients that are nonbiodegradable and can wash off of skin{{Cite web |title=Protect Yourself, Protect The Reef! The impacts of sunscreens on our coral reefs |url=http://cdhc.noaa.gov/_docs/Site%20Bulletin_Sunscreen_final.pdf |publisher=U.S. National Park Service |access-date=1 July 2013 |archive-date=13 February 2013 |archive-url=https://web.archive.org/web/20130213222809/http://cdhc.noaa.gov/_docs/Site%20Bulletin_Sunscreen_final.pdf |url-status=live}}{{Cite web |url=http://www.badgerbalm.com/s-35-coral-reef-safe-sunscreen.aspx|title=Coral Reef Safe Sunscreen |website=badgerbalm.com |access-date=24 March 2014 |archive-date=24 March 2014 |archive-url=https://web.archive.org/web/20140324220654/http://www.badgerbalm.com/s-35-coral-reef-safe-sunscreen.aspx |url-status=live}}{{Cite journal |vauthors=Danovaro R, Bongiorni L, Corinaldesi C, Giovannelli D, Damiani E, Astolfi P, Greci L, Pusceddu A |title=Sunscreens cause coral bleaching by promoting viral infections |journal=Environmental Health Perspectives |volume=116 |issue=4 |pages=441–7 |date=April 2008 |pmid=18414624 |pmc=2291018 |doi=10.1289/ehp.10966 }}{{Cite journal |vauthors=Downs CA, Kramarsky-Winter E, Fauth JE, Segal R, Bronstein O, Jeger R, Lichtenfeld Y, Woodley CM, Pennington P, Kushmaro A, Loya Y |title=Toxicological effects of the sunscreen UV filter, benzophenone-2, on planulae and in vitro cells of the coral, Stylophora pistillata |journal=Ecotoxicology |volume=23 |issue=2 |pages=175–91 |date=March 2014 |pmid=24352829 |doi=10.1007/s10646-013-1161-y |bibcode=2014Ecotx..23..175D |s2cid=1505199 }}
• ocean acidification due to elevated levels of CO₂ caused by air pollution{{Cite journal |vauthors=Anthony KR, Kline DI, Diaz-Pulido G, Dove S, Hoegh-Guldberg O |title=Ocean acidification causes bleaching and productivity loss in coral reef builders |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=105 |issue=45 |pages=17442–6 |date=November 2008 |pmid=18988740 |pmc=2580748 |doi=10.1073/pnas.0804478105 |bibcode=2008PNAS..10517442A |doi-access=free }}
• being exposed to oil or other chemical spills{{Cite web |url=https://response.restoration.noaa.gov/about/media/how-do-oil-spills-affect-coral-reefs.html|title=How Do Oil Spills Affect Coral Reefs? |website=response.restoration.noaa.gov |access-date=24 April 2018 |archive-date=24 April 2018 |archive-url=https://web.archive.org/web/20180424135634/https://response.restoration.noaa.gov/about/media/how-do-oil-spills-affect-coral-reefs.html |url-status=live}}
• changes in water chemistry, particularly an imbalance in the ratio of the macronutrients nitrate and phosphate{{Cite journal |last1=Wiedenmann |first1=Jörg |last2=D'Angelo |first2=Cecilia |last3=Smith |first3=Edward G. |last4=Hunt |first4=Alan N. |last5=Legiret |first5=François-Eric |last6=Postle |first6=Anthony D. |last7=Achterberg |first7=Eric P. |date=February 2013 |title=Nutrient enrichment can increase the susceptibility of reef corals to bleaching |url=https://www.nature.com/articles/nclimate1661 |journal=Nature Climate Change |language=en |volume=3 |issue=2 |pages=160–164 |doi=10.1038/nclimate1661 |bibcode=2013NatCC...3..160W |issn=1758-6798}}
• meteorological conditions{{Cite journal |last1=Richards |first1=Lara Shania |last2=Siems |first2=Steven Thomas |last3=Huang |first3=Yi |last4=Zhao |first4=Wenhui |last5=Harrison |first5=Daniel Patrick |last6=Manton |first6=Michael John |last7=Reeder |first7=Michael John |date=2024-10-12 |title=The meteorological drivers of mass coral bleaching on the central Great Barrier Reef during the 2022 La Niña |journal=Scientific Reports |language=en |volume=14 |issue=1 |pages=23867 |doi=10.1038/s41598-024-74181-2 |issn=2045-2322 |pmc=11470093 |pmid=39394244}}

{{See also|Effects of climate change on oceans}}

Extreme bleaching events are directly linked with climate-induced phenomena that increase ocean temperature, such as El Niño-Southern Oscillation (ENSO).{{Cite journal |last1=Baker |first1=Andrew C. |last2=Glynn |first2=Peter W. |last3=Riegl |first3=Bernhard |date=December 2008 |title=Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook |url=https://doi.org/10.1016/j.ecss.2008.09.003 |journal=Estuarine, Coastal and Shelf Science |volume=80 |issue=4 |pages=435–471 |doi=10.1016/j.ecss.2008.09.003 |bibcode=2008ECSS...80..435B |issn=0272-7714}} The warming ocean surface waters can lead to bleaching of corals which can cause serious damage and coral death. The IPCC Sixth Assessment Report in 2022 found that: "Since the early 1980s, the frequency and severity of mass coral bleaching events have increased sharply worldwide".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: [https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Chapter03.pdf Chapter 3: Oceans and Coastal Ecosystems and Their Services]. In: [https://www.ipcc.ch/report/ar6/wg2/ Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 379–550, doi:10.1017/9781009325844.005.{{rp|416}} Coral reefs, as well as other shelf-sea ecosystems, such as rocky shores, kelp forests, seagrasses, and mangroves, have recently undergone mass mortalities from marine heatwaves.{{rp|381}} It is expected that many coral reefs will "undergo irreversible phase shifts due to marine heatwaves with global warming levels >1.5°C".{{rp|382}}

This problem was already identified in 2007 by the Intergovernmental Panel on Climate Change (IPCC) as the greatest threat to the world's reef systems.{{Cite book |author=IPCC |chapter=Summary for policymakers |chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-spm.pdf |veditors=Parry ML, Canziani OF, Palutikof JP, van der Linden PJ, Hanson CE |title=Climate Change 2007: impacts, adaptation and vulnerability: contribution of Working Group II to the fourth assessment report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press |location=Cambridge, UK |year=2007 |pages=7–22 |isbn=978-0-521-70597-4 |access-date=8 July 2009 |archive-date=13 January 2018 |archive-url=https://web.archive.org/web/20180113141313/http://www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-spm.pdf |url-status=live }}{{Cite book |vauthors=Fischlin A, Midgley GF, Price JT, Leemans R, Gopal B, Turley C, Rounsevell MD, Dube OP, Tarazona J, Velichko AA |chapter=Ch 4. Ecosystems, their properties, goods and services |chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-chapter4.pdf |veditors=Parry ML, Canziani OF, Palutikof JP, van der Linden PJ, Hanson CE |title=Climate Change 2007: impacts, adaptation and vulnerability: contribution of Working Group II to the fourth assessment report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press |location=Cambridge, UK |year=2007 |pages=211–72 |isbn=978-0-521-70597-4 |access-date=8 July 2009 |archive-date=11 October 2017 |archive-url=https://web.archive.org/web/20171011185727/http://www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-chapter4.pdf |url-status=live }}

The Great Barrier Reef experienced its first major bleaching event in 1998. Since then, bleaching events have increased in frequency, with three events occurring in the years 2016–2020.{{Cite news |last1=Davidson |first1=Jordan |date=25 March 2020 |title=Great Barrier Reef Has Third Major Bleaching Event in Five Years |agency=Ecowatch |url=https://www.ecowatch.com/coral-bleaching-great-barrier-reef-2645576557.html |access-date=27 March 2020}} Bleaching is predicted to occur three times a decade on the Great Barrier Reef if warming is kept to 1.5 °C, increasing every other year to 2 °C.{{cite journal |last1=McWhorter |first1=Jennifer K. |last2=Halloran |first2=Paul R. |last3=Roff |first3=George |last4=Skirving |first4=William J. |last5=Perry |first5=Chris T. |last6=Mumby |first6=Peter J. |title=The importance of 1.5°C warming for the Great Barrier Reef |journal=Global Change Biology |date=February 2022 |volume=28 |issue=4 |pages=1332–1341 |doi=10.1111/gcb.15994 |pmid=34783126 |bibcode=2022GCBio..28.1332M |hdl=10871/127948 |s2cid=244131267 |hdl-access=free }}

With the increase of coral bleaching events worldwide, National Geographic noted in 2017, "In the past three years, 25 reefs—which comprise three-fourths of the world's reef systems—experienced severe bleaching events in what scientists concluded was the worst-ever sequence of bleachings to date."{{Cite web |url=https://news.nationalgeographic.com/2017/06/coral-reef-bleaching-global-warming-unesco-sites/|title=Coral Reefs Could Be Gone in 30 Years |date=2017-06-23 |website=National Geographic News |access-date=2019-05-07 |archive-date=7 May 2019 |archive-url=https://web.archive.org/web/20190507044023/https://news.nationalgeographic.com/2017/06/coral-reef-bleaching-global-warming-unesco-sites/ |url-status=dead}}

In a study conducted on the Hawaiian mushroom coral Lobactis scutaria, researchers discovered that higher temperatures and elevated levels of photosynthetically active radiation (PAR) had a detrimental impact on its reproductive physiology. The purpose of this study was to investigate the survival of reef-building corals in their natural habitat, as coral reproduction is being hindered by the effects of climate change.{{Cite journal |last1=Bouwmeester |first1=Jessica |last2=Daly |first2=Jonathan |last3=Zuchowicz |first3=Nikolas |last4=Lager |first4=Claire |last5=Henley |first5=E. Michael |last6=Quinn |first6=Mariko |last7=Hagedorn |first7=Mary |date=2023-01-05 |title=Solar radiation, temperature and the reproductive biology of the coral Lobactis scutaria in a changing climate |url=http://dx.doi.org/10.1038/s41598-022-27207-6 |journal=Scientific Reports |volume=13 |issue=1 |page=246 |doi=10.1038/s41598-022-27207-6 |pmid=36604569 |issn=2045-2322|pmc=9816315 |bibcode=2023NatSR..13..246B }}

File:Keppelbleaching.jpg coral with normal coral in the background]]

Elevated sea water temperatures are the main cause of mass bleaching events.{{Cite journal |last2=Glynn |first2=Peter W. |last3=Riegl |first3=Bernhard |name-list-style=vanc |year=2008 |title=Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook |journal=Estuarine, Coastal and Shelf Science |volume=80 |issue=4 |pages=435–71 |bibcode=2008ECSS...80..435B |doi=10.1016/j.ecss.2008.09.003 |last1=Baker |first1=Andrew C.}} Sixty major episodes of coral bleaching have occurred between 1979 and 1990,{{Cite journal |last1=Chumkiew |first1=Sirilak |last2=Jaroensutasinee |first2=Mullica |last3=Jaroensutasinee |first3=Krisanadej |name-list-style=vanc |title=Impact of Global Warming on Coral Reefs |journal=Walailak Journal of Science and Technology |volume=8 |issue=2 |year=2011 |pages=111–29 |url=http://wjst.wu.ac.th/index.php/wjst/article/view/17 |access-date=2 August 2016 |archive-date=6 August 2016 |archive-url=https://web.archive.org/web/20160806175300/http://wjst.wu.ac.th/index.php/wjst/article/view/17 |url-status=live }}{{Cite journal |vauthors=Huppert A, Stone L |title=Chaos in the Pacific's coral reef bleaching cycle |journal=The American Naturalist |volume=152 |issue=3 |pages=447–59 |date=September 1998 |pmid=18811451 |doi=10.1086/286181 |bibcode=1998ANat..152..447H |s2cid=29245066 }} with the associated coral mortality affecting reefs in every part of the world. In 2016, the longest coral bleaching event was recorded.{{Cite news |last=McDermott |first=Amy |date=22 June 2016 |title=Coral bleaching event is longest on record |url=https://www.sciencenews.org/article/coral-bleaching-event-longest-record |newspaper=Science News |access-date=25 July 2016 |archive-date=16 August 2016 |archive-url=https://web.archive.org/web/20160816161024/https://www.sciencenews.org/article/coral-bleaching-event-longest-record |url-status=live }} The longest and most destructive coral bleaching event was because of the El Niño that occurred from 2014 to 2017.{{Cite journal |vauthors=Albright R |title=Can We Save the Corals? |journal=Scientific American |volume=318 |issue=1 |pages=42–49 |date=December 2017 |pmid=29257818 |doi=10.1038/scientificamerican0118-42 |bibcode=2017SciAm.318a..42A }} During this time, over 70 percent of the coral reefs around the world have become damaged.

Factors that influence the outcome of a bleaching event include stress-resistance which reduces bleaching, tolerance to the absence of zooxanthellae, and how quickly new coral grows to replace the dead. Due to the patchy nature of bleaching, local climatic conditions such as shade or a stream of cooler water can reduce bleaching incidence. Coral and zooxanthellae health and genetics also influence bleaching.{{Cite book |last1=Marshall |first1=Paul |last2=Schuttenberg |first2=Heidi |name-list-style=vanc |title=A Reef Manager's Guide to Coral Bleaching |publisher=Great Barrier Reef Marine Park Authority |year=2006 |location=Townsville, Australia |pages=78–79 |url=http://www.gbrmpa.gov.au/__data/assets/pdf_file/0013/4450/Gbrmpa-ReefManagersGuidetoCoralBleaching.pdf |isbn=978-1-876945-40-4 |access-date=23 May 2014 |archive-date=13 February 2014 |archive-url=https://web.archive.org/web/20140213071105/http://www.gbrmpa.gov.au/__data/assets/pdf_file/0013/4450/Gbrmpa-ReefManagersGuidetoCoralBleaching.pdf |url-status=live }}

Large coral colonies such as Porites are able to withstand extreme temperature shocks, while fragile branching corals such Acropora are far more susceptible to stress following a temperature change.{{Cite journal |last1=Baird |first1=Ah |last2=Marshall |first2=Pa |date=2002 |title=Mortality, growth and reproduction in scleractinian corals following bleaching on the Great Barrier Reef |url=http://www.int-res.com/abstracts/meps/v237/p133-141/ |journal=Marine Ecology Progress Series |language=en |volume=237 |pages=133–141 |doi=10.3354/meps237133 |bibcode=2002MEPS..237..133B |issn=0171-8630|doi-access=free }} Corals consistently exposed to low-stress levels may be more resistant to bleaching.Gabriel D. Grinmsditch and Rodney V. Salm, [http://data.iucn.org/dbtw-wpd/edocs/2006-042.pdf Coral Reef Resilience and Resistance to Bleaching] {{Webarchive|url=https://web.archive.org/web/20121028140722/http://data.iucn.org/dbtw-wpd/edocs/2006-042.pdf |date=28 October 2012 }}, "IUCN: The World Conservation Union", 2006{{page needed|date=August 2016}}{{Cite journal |vauthors=Iguchi A, Ozaki S, Nakamura T, Inoue M, Tanaka Y, Suzuki A, Kawahata H, Sakai K |title=Effects of acidified seawater on coral calcification and symbiotic algae on the massive coral Porites australiensis |journal=Marine Environmental Research |volume=73 |pages=32–6 |date=February 2012 |pmid=22115919 |doi=10.1016/j.marenvres.2011.10.008 |bibcode=2012MarER..73...32I }}

Scientists believe that the oldest known bleaching was that of the Late Devonian (Frasnian/Famennian), also triggered by the rise of sea surface temperatures. It resulted in the demise of the largest coral reefs in the Earth's history.{{Cite journal |last1=Bridge |first1=Tom C. L. |last2=Baird |first2=Andrew H. |last3=Pandolfi |first3=John M. |last4=McWilliam |first4=Michael J. |last5=Zapalski |first5=Mikołaj K. |date=2022-01-26 |title=Functional consequences of Palaeozoic reef collapse |journal=Scientific Reports |language=en |volume=12 |issue=1 |pages=1386 |doi=10.1038/s41598-022-05154-6 |pmid=35082318 |pmc=8792005 |bibcode=2022NatSR..12.1386B |issn=2045-2322}}{{Cite journal |vauthors=Zapalski MK, Nowicki J, Jakubowicz M, Berkowski B |year=2017 |title=Tabulate corals across the Frasnian/Famennian boundary: architectural turnover and its possible relation to ancient photosymbiosis |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=487 |pages=416–429 |doi=10.1016/j.palaeo.2017.09.028 |bibcode=2017PPP...487..416Z }}

According to Clive Wilkinson of Global Coral Reef Monitoring Network of Townsville, Australia, in 1998 the mass bleaching event that occurred in the Indian Ocean region was due to the rising of sea temperatures by 2 °C coupled with the strong El Niño event in 1997–1998.{{Cite journal |last=Wilkinson |first=C. P. |date=1998 |title=The 1997–1998 Mass Bleaching Event Around the World |url=https://aquadocs.org/handle/1834/545 |language=en |website=AquaDocs }}

In April 2024 a 4th global coral bleaching event was confirmed by NOAA{{Cite journal |last1=McWhorter |first1=Jennifer K. |last2=Halloran |first2=Paul R. |last3=Roff |first3=George |last4=Mumby |first4=Peter J. |date=2024-04-16 |title=Climate change impacts on mesophotic regions of the Great Barrier Reef |journal=Proceedings of the National Academy of Sciences |language=en |volume=121 |issue=16 |pages=e2303336121 |doi=10.1073/pnas.2303336121 |pmid=38588432 |pmc=11032494 |bibcode=2024PNAS..12103336M |issn=0027-8424|hdl=10871/135524 |hdl-access=free }}{{Cite web |date=2024-04-15 |title=NOAA confirms 4th global coral bleaching event {{!}} National Oceanic and Atmospheric Administration |url=https://www.noaa.gov/news-release/noaa-confirms-4th-global-coral-bleaching-event |access-date=2024-04-16 |website=www.noaa.gov |language=en}}{{Cite news |date=2024-04-15 |title=Coral bleaching: Fourth global mass stress episode underway - US scientists |url=https://www.bbc.com/news/science-environment-68814016 |access-date=2024-04-16 |language=en-GB}} The share of affected coral reefs worldwide by each of the four bleaching events has been estimated to be 20%, 35%, 56% and 54%.{{Cite web |title=State of the Oceans 2024 report |url=https://www.statista.com/site/state-of-the-oceans |access-date=2024-08-03 |website=German Ocean Foundation (Deutsche meeresstiftung) & Statista |language=en}}{{Cite web |date=2024-06-07 |title=Infographic: The Extent of Global Coral Bleaching Events |url=https://www.statista.com/chart/32383/the-extent-of-global-coral-bleaching-events |access-date=2024-08-03 |website=Statista Daily Data |language=en}}

Preceding this, the second major coral bleaching crisis of this decade began in February 2023, affecting reefs across 54 nations in all major ocean basins. This event has led to severe damage, with coral mortalities reaching up to 93% in areas like the Pacific coast near Mexico. The economic implications are profound, as coral reefs contribute approximately $2.7 trillion annually to the global economy, including $36 billion from tourism alone. Although a forthcoming shift to a La Niña phase may offer some relief, regions such as Florida have already experienced complete die-offs in some reefs, where temperatures have risen to 101°F (38.3°C). Moreover, the Great Barrier Reef is undergoing its fifth extensive bleaching event since 2016, underscoring the persistent and serious risks these vital ecosystems face.{{Cite news |date=2024-04-16 |title=Heat Stress Is Plunging the World's Coral Reefs Into Crisis |url=https://www.bloomberg.com/news/articles/2024-04-16/record-ocean-temperatures-are-plunging-the-world-s-coral-reefs-into-crisis |access-date=2024-04-16 |work=Bloomberg.com |language=en}}

File:GBReef TempChlorophyll 200602.jpg showing that the warmest water (top picture) coincides with the coral reefs (lower picture), setting up conditions that can cause coral bleaching.]]

File:Lascar Diving at the The Great Barrier Reef (4559842029).jpg

Coral bleaching events and the subsequent loss of coral coverage often result in the decline of fish diversity. The loss of diversity and abundance in herbivorous fish particularly affect coral reef ecosystems.{{Cite journal |last1=Pratchett |first1=Morgan S. |last2=Hoey |first2=Andrew S. |last3=Wilson |first3=Shaun K. |last4=Messmer |first4=Vanessa |last5=Graham |first5=Nicholas A. J. |date=2011-09-01 |title=Changes in Biodiversity and Functioning of Reef Fish Assemblages following Coral Bleaching and Coral Loss |journal=Diversity |language=en |volume=3 |issue=3 |pages=424–452 |doi=10.3390/d3030424 |issn=1424-2818 |doi-access=free |hdl=10754/334624 |hdl-access=free }} As mass bleaching events occur more frequently, fish populations will continue to homogenize. Smaller and more specialized fish species that fill particular ecological niches that are crucial for coral health are replaced by more generalized species. The loss of specialization likely contributes to the loss of resilience in coral reef ecosystems after bleaching events.{{Cite web |title=The Hidden Coral Crisis: Loss of Fish Diversity After Bleaching Strikes |url=https://www.newsdeeply.com/oceans/articles/2018/04/10/the-hidden-coral-crisis-loss-of-fish-diversity-after-bleaching-strikes |access-date=2020-07-02 |website=Oceans |date=10 April 2018 |language=en |archive-date=26 June 2020 |archive-url=https://web.archive.org/web/20200626182853/https://www.newsdeeply.com/oceans/articles/2018/04/10/the-hidden-coral-crisis-loss-of-fish-diversity-after-bleaching-strikes |url-status=live}}

According to Brian Skoloff of The Christian Science Monitor, "If the reefs vanished, experts say, hunger, poverty and political instability could ensue."Skoloff, Brian (26 March 2010) [http://www.csmonitor.com/From-the-news-wires/2010/0326/Death-of-coral-reefs-could-devastate-nations Death of coral reefs could devastate nations] {{Webarchive|url=https://web.archive.org/web/20121113194547/http://www.csmonitor.com/From-the-news-wires/2010/0326/Death-of-coral-reefs-could-devastate-nations |date=13 November 2012 }}, The Christian Science Monitor Since countless sea life depend on the reefs for shelter and protection from predators, the extinction of the reefs would ultimately create a domino effect that would trickle down to the many human societies that depend on those fish for food and livelihood. There has been a 44% decline in coral reefs over the last 20 years in the Florida Keys and up to 80% in the Caribbean alone.{{Cite web |date=5 December 2012 |title=Endangered Coral Reefs Die as Ocean Temperatures Rise and Water Turns Acidic |url=https://www.pbs.org/newshour/bb/climate-change-jan-june13-pledge_06-04/ |url-status=dead |archive-url=https://web.archive.org/web/20171012191456/http://www.pbs.org/newshour/bb/climate-change-jan-june13-pledge_06-04/ |archive-date=12 October 2017 |website=PBS Newshour}}

Coral reefs provide various ecosystem services, one of which is being a natural fishery, as many frequently consumed commercial fish spawn or live out their juvenile lives in coral reefs around the tropics.{{Cite journal |last1=Speers |first1=Ann E. |last2=Besedin |first2=Elena Y. |last3=Palardy |first3=James E. |last4=Moore |first4=Chris |name-list-style=vanc |date=1 August 2016|title=Impacts of climate change and ocean acidification on coral reef fisheries: An integrated ecological–economic model |journal=Ecological Economics |volume=128 |pages=33–43 |doi=10.1016/j.ecolecon.2016.04.012|bibcode=2016EcoEc.128...33S }}{{Cite journal |last1=Chen |first1=Ping-Yu |last2=Chen |first2=Chi-Chung |last3=Chu |first3=LanFen |last4=McCarl |first4=Bruce |name-list-style=vanc |date=1 January 2015 |title=Evaluating the economic damage of climate change on global coral reefs |journal=Global Environmental Change |volume=30 |pages=12–20 |doi=10.1016/j.gloenvcha.2014.10.011|bibcode=2015GEC....30...12C }}{{Cite journal |vauthors=Teh LS, Teh LC, Sumaila UR |title=A Global Estimate of the Number of Coral Reef Fishers |journal=PLOS ONE |volume=8 |issue=6 |pages=e65397 |date=19 June 2013 |pmid=23840327 |pmc=3686796 |doi=10.1371/journal.pone.0065397 |bibcode=2013PLoSO...865397T |doi-access=free }} Thus, reefs are a popular fishing site and are an important source of income for fishers, especially small, local fisheries. As coral reef habitat decreases due to bleaching, reef associated fish populations also decrease, which affects fishing opportunities. A model from one study by Speers et al. calculated direct losses to fisheries from decreased coral cover to be around $49–69 billion, if human societies continue to emit high levels of greenhouse gases. But, these losses could be reduced for a consumer surplus benefit of about $14–20 billion, if societies chose to emit a lower level of greenhouse gases instead. These economic losses also have important political implications, as they fall disproportionately on developing countries where the reefs are located, namely in Southeast Asia and around the Indian Ocean.{{Cite journal |vauthors=Wolff NH, Donner SD, Cao L, Iglesias-Prieto R, Sale PF, Mumby PJ |title=Global inequities between polluters and the polluted: climate change impacts on coral reefs |journal=Global Change Biology |volume=21 |issue=11 |pages=3982–94 |date=November 2015 |pmid=26234736 |doi=10.1111/gcb.13015 |bibcode=2015GCBio..21.3982W |s2cid=23157593 }} It would cost more for countries in these areas to respond to coral reef loss as they would need to turn to different sources of income and food, in addition to losing other ecosystem services such as ecotourism. A study completed by Chen et al. suggested that the commercial value of reefs decreases by almost 4% every time coral cover decreases by 1% because of losses in ecotourism and other potential outdoor recreational activities.

Coral reefs also act as a protective barrier for coastlines by reducing wave impact, which lowers the damage from storms, erosions, and flooding. Countries that lose this natural protection will lose more money because of the increased susceptibility of storms. This indirect cost, combined with the lost revenue from tourism, will result in enormous economic effects.

The US National Oceanic and Atmospheric Administration (NOAA) monitors for bleaching "hot spots", areas where sea surface temperature rises 1 °C or more above the long-term monthly average. The "hot spots" are the locations in which thermal stress is measured, and with the development of Degree Heating Week (DHW), the coral reef's thermal stress is monitored.{{Cite journal |last1=Liu |first1=Gang |last2=Strong |first2=Alan E. |last3=Skirving |first3=William |s2cid=128559504 |name-list-style=vanc |date=15 April 2003 |title=Remote sensing of sea surface temperatures during 2002 Barrier Reef coral bleaching |journal=Eos, Transactions American Geophysical Union |volume=84 |issue=15 |pages=137–141 |doi=10.1029/2003EO150001 |bibcode=2003EOSTr..84..137L|doi-access=free }}{{Cite journal |vauthors=McClanahan TR, Ateweberhan M, Sebastián CR, Graham NJ, Wilson SK, Bruggemann JH, Guillaume MM |date=1 September 2007 |title=Predictability of coral bleaching from synoptic satellite and in situ temperature observations |journal=Coral Reefs |volume=26 |issue=3 |pages=695–701 |doi=10.1007/s00338-006-0193-7 |s2cid=7435285}} Global coral bleaching is being detected earlier due to the satellite remote sensing of the rise of sea temperatures.Liu, Gang & Strong, Alan & Skirving, William & Arzayus, Felipe. (2005). [https://www.researchgate.net/publication/284342045 Overview of NOAA coral reef watch program's near-real time satellite global coral bleaching monitoring activities] {{Webarchive|url=https://web.archive.org/web/20180930033623/https://www.researchgate.net/publication/284342045 |date=30 September 2018 }}. Proc 10th Int Coral Reef Symp. 1. pp. 1783–1793. It is necessary to monitor the high temperatures because coral bleaching events are affecting coral reef reproduction and normal growth capacity, as well as it weakening corals, eventually leading to their mortality. This system detected the worldwide 1998 bleaching event,{{Cite web |title=NOAA Hotspots |date=19 October 2006 |url=http://coral.aoml.noaa.gov/pipermail/coral-list/2006-October/003757.html |publisher=coral.aoml.noaa.gov |access-date=1 November 2007 |archive-date=16 July 2011 |archive-url=https://web.archive.org/web/20110716212139/http://coral.aoml.noaa.gov/pipermail/coral-list/2006-October/003757.html |url-status=live }}{{Cite web |title=Pro-opinion of NOAA Hotspots |url=http://www.osdpd.noaa.gov |access-date=23 July 2021 |archive-date=12 May 2015 |archive-url=https://web.archive.org/web/20150512062553/http://www.osdpd.noaa.gov/ |url-status=live }} that corresponded to the 1997–98 El Niño event.{{Cite web |last=NOAA Coral Reef Watch |title=Methodology, Product Description, and Data Availability of Coral Reef Watch Operational and Experimental Satellite Coral Bleaching Monitoring Products |url=http://coralreefwatch.noaa.gov/satellite/methodology/methodology.php#sst |publisher=NOAA |access-date=27 February 2014 |archive-date=7 March 2014 |archive-url=https://web.archive.org/web/20140307055310/http://coralreefwatch.noaa.gov/satellite/methodology/methodology.php#sst |url-status=live}} Currently, 190 reef sites around the globe are monitored by the NOAA, and send alerts to research scientists and reef managers via the NOAA Coral Reef Watch (CRW) website.{{Cite journal |vauthors=Maynard JA, Johnson JE, Marshall PA, Eakin CM, Goby G, Schuttenberg H, Spillman CM |title=A strategic framework for responding to coral bleaching events in a changing climate |journal=Environmental Management |volume=44 |issue=1 |pages=1–11 |date=July 2009 |pmid=19434447 |doi=10.1007/s00267-009-9295-7 |bibcode=2009EnMan..44....1M |s2cid=30321497 }} By monitoring the warming of sea temperatures, the early warnings of coral bleaching alert reef managers to prepare for and draw awareness to future bleaching events. The first mass global bleaching events were recorded in 1998 and 2010, which was when the El Niño caused the ocean temperatures to rise and worsened the corals living conditions. The 2014–2017 El Niño was recorded to be the longest and most damaging to the corals, which harmed over 70% of our coral reefs. Over two-thirds of the Great Barrier Reef have been reported to be bleached or dead.

To accurately monitoring the extent and evolution of bleaching events, scientist are using underwater photogrammetric techniques to create accurate orthophoto of coral reefs transects and AI-assisted image segmentation with open source tools like TagLab to identify from these photos the health status of the corals.{{Cite journal |last1=Kopecky |first1=Kai L. |last2=Pavoni |first2=Gaia |last3=Nocerino |first3=Erica |last4=Brooks |first4=Andrew J. |last5=Corsini |first5=Massimiliano |last6=Menna |first6=Fabio |last7=Gallagher |first7=Jordan P. |last8=Capra |first8=Alessandro |last9=Castagnetti |first9=Cristina |last10=Rossi |first10=Paolo |last11=Gruen |first11=Armin |last12=Neyer |first12=Fabian |last13=Muntoni |first13=Alessandro |last14=Ponchio |first14=Federico |last15=Cignoni |first15=Paolo |date=August 2023 |title=Quantifying the Loss of Coral from a Bleaching Event Using Underwater Photogrammetry and AI-Assisted Image Segmentation |journal=Remote Sensing |language=en |volume=15 |issue=16 |pages=4077 |doi=10.3390/rs15164077 |bibcode=2023RemS...15.4077K |issn=2072-4292 |doi-access=free |hdl=11380/1316375 |hdl-access=free }}File:Ocean Acidification.jpg]

Increasing ocean acidification due to rises in carbon dioxide levels exacerbates the bleaching effects of thermal stress. Acidification affects the corals' ability to create calcareous skeletons, essential to their survival.{{Cite news |last=Lang |first=Susan |title=Major international study warns global warming is destroying coral reefs and calls for 'drastic actions' |url=http://www.news.cornell.edu/stories/Dec07/climate.kills.coral.sl.html |access-date=8 August 2011 |newspaper=Cornell Chronicle |date=13 December 2007 |archive-date=6 August 2011 |archive-url=https://web.archive.org/web/20110806070338/http://www.news.cornell.edu/stories/Dec07/climate.kills.coral.sl.html |url-status=live}}{{Cite journal |last=Kleypas |first=J. A. |author-link=Joan Kleypas |date=1999-04-02 |title=Geochemical Consequences of Increased Atmospheric Carbon Dioxide on Coral Reefs |url=https://www.science.org/doi/10.1126/science.284.5411.118 |journal=Science |volume=284 |issue=5411 |pages=118–120 |doi=10.1126/science.284.5411.118 |pmid=10102806 |bibcode=1999Sci...284..118K |access-date=10 June 2021 |archive-date=23 July 2021 |archive-url=https://web.archive.org/web/20210723092515/https://science.sciencemag.org/content/284/5411/118 |url-status=live}} This is because ocean acidification decreases the amount of carbonate ion in the water, making it more difficult for corals to absorb the calcium carbonate they need for the skeleton. As a result, the resilience of reefs goes down, while it becomes easier for them to erode and dissolve.{{Cite book |title=Coral Reefs of the Eastern Tropical Pacific |last1=Manzello |first1=Derek P. |last2=Eakin |first2=C. Mark |last3=Glynn |first3=Peter W. |chapter=Effects of Global Warming and Ocean Acidification on Carbonate Budgets of Eastern Pacific Coral Reefs |name-list-style=vanc |date=2017 |publisher=Springer, Dordrecht |isbn=9789401774987 |series=Coral Reefs of the World |volume=8 |pages=517–533 |doi=10.1007/978-94-017-7499-4_18}} In addition, the increase in CO₂ allows herbivore overfishing and nutrification to change coral-dominated ecosystems to algal-dominated ecosystems.{{Cite journal |last1=Anthony |first1=Kenneth R. N. |last2=Maynard |first2=Jeffrey A. |last3=Diaz-Pulido |first3=Guillermo |last4=Mumby |first4=Peter J. |last5=Marshall |first5=Paul A. |last6=Cao |first6=Long |last7=Hoegh-Guldberg |first7=Ove |author-link7=Ove Hoegh-Guldberg (biologist) |name-list-style=vanc |date=1 May 2011 |title=Ocean acidification and warming will lower coral reef resilience |journal=Global Change Biology |volume=17 |issue=5 |pages=1798–1808 |doi=10.1111/j.1365-2486.2010.02364.x |pmc=3597261 |bibcode=2011GCBio..17.1798A}} A recent study from the Atkinson Center for a Sustainable Future found that with the combination of acidification and temperature rises, the levels of CO₂ could become too high for coral to survive in as little as 50 years.

File:Bleached coral (24577819729).jpg in Australia.]]Zooxanthellae are a type of dinoflagellate that live within the cytoplasm of many marine invertebrates.{{Cite web |title=Zooxanthella {{!}} Definition of Zooxanthella by Oxford Dictionary on Lexico.com also meaning of Zooxanthella |url=https://www.lexico.com/en/definition/zooxanthella |access-date=2020-11-10 |website=Lexico Dictionaries {{!}} English |language=en |archive-date=16 November 2020 |archive-url=https://web.archive.org/web/20201116082118/https://www.lexico.com/en/definition/zooxanthella |url-status=dead}} Members of the phylum Dinoflagellata, they are round microalgae that share a symbiotic relationship with their host. They are also part of the genus Symbiodinium and Kingdom Alveolata. These organisms are phytoplankton and therefore photosynthesize. The host organism harnesses the products of photosynthesis, i.e. oxygen, sugar, etc., and in exchange, the zooxanthellae are offered housing and protection, as well as carbon dioxide, phosphates, and other essential inorganic compounds that help them to survive and thrive. Zooxanthellae share 95% of the products of photosynthesis with their host coral.{{Cite journal |last=Smith |first=D.J |year=2005 |title=Is photoinhibition of zooxanthellae photosynthesis the primary cause of thermal bleaching in corals?|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1529-8817.2003.00895.x |access-date=9 November 2020 |journal=Global Change Biology |volume=11 |issue=1 |pages=1–11 |doi=10.1111/j.1529-8817.2003.00895.x |bibcode=2005GCBio..11....1S |s2cid=42629591 |archive-date=20 November 2020 |archive-url=https://web.archive.org/web/20201120025830/https://onlinelibrary.wiley.com/doi/full/10.1111/j.1529-8817.2003.00895.x |url-status=live}} According to a study done by D.J. Smith et al., photoinhibition is a likely factor in coral bleaching.{{Cite journal |last=Smith |first=D.J |year=2005 |title=Is photoinhibition of zooxanthellae photosynthesis the primary cause of thermal bleaching in corals? |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1529-8817.2003.00895.x |journal=Global Change Biology |volume=11 |issue=1 |page=1 |bibcode=2005GCBio..11....1S |doi=10.1111/j.1529-8817.2003.00895.x |s2cid=42629591 |via=Online Library |access-date=23 July 2021 |archive-date=28 November 2020 |archive-url=https://web.archive.org/web/20201128024639/https://onlinelibrary.wiley.com/doi/10.1111/j.1529-8817.2003.00895.x |url-status=live}} It also suggests that the hydrogen peroxide produced in zooxanthealle plays a role in signaling themselves to flee the corals. Photo-inhibition of Zooxanthellae can be caused by exposure to UV filters found in personal care products.{{Cite journal |last1=Zhong |first1=Xin |last2=Downs |first2=Craig A. |last3=Che |first3=Xingkai |last4=Zhang |first4=Zishan |last5=Li |first5=Yiman |last6=Liu |first6=Binbin |last7=Li |first7=Qingming |last8=Li |first8=Yuting |last9=Gao |first9=Huiyuan |date=2019-11-01 |title=The toxicological effects of oxybenzone, an active ingredient in suncream personal care products, on prokaryotic alga Arthrospira sp. and eukaryotic alga Chlorella sp. |url=http://www.sciencedirect.com/science/article/pii/S0166445X19305934 |journal=Aquatic Toxicology |language=en |volume=216 |pages=105295 |doi=10.1016/j.aquatox.2019.105295 |pmid=31561136 |bibcode=2019AqTox.21605295Z |s2cid=202862335 |issn=0166-445X |access-date=20 November 2020 |archive-date=23 July 2021 |archive-url=https://web.archive.org/web/20210723092509/https://www.sciencedirect.com/science/article/abs/pii/S0166445X19305934 |url-status=live}} In a study done by Zhong et al., Oxybenzone (BP-3) had the most negative effects on zooxanthellae health. The combination of temperature increase and presence of UV filters in the ocean has further decreased zooxanthellae health.{{Cite journal |last1=Wijgerde |first1=Tim |last2=van Ballegooijen |first2=Mike |last3=Nijland |first3=Reindert |last4=van der Loos |first4=Luna |last5=Kwadijk |first5=Christiaan |last6=Osinga |first6=Ronald |last7=Murk |first7=Albertinka |last8=Slijkerman |first8=Diana |date=2019-12-20 |title=Adding insult to injury: Effects of chronic oxybenzone exposure and elevated temperature on two reef-building corals |url=http://dx.doi.org/10.1101/2019.12.19.882332 |access-date=2020-11-20 |journal=bioRxiv |doi=10.1101/2019.12.19.882332 |s2cid=214573850 |archive-date=23 July 2021 |archive-url=https://web.archive.org/web/20210723092550/https://www.biorxiv.org/content/10.1101/2019.12.19.882332v1 |url-status=live}} The combination of UV filters and higher temperatures led to an additive effect on photo-inhibition and overall stress on coral species.

Following bleaching events, there has been a rise in the global disease outbreak among coral populations. This is due to the weakened state of the corals that makes them susceptible to infection caused by disease-carrying pathogens. Infectious bacteria of the species Vibrio shiloi are the bleaching agent of Oculina patagonica in the Mediterranean Sea, causing this effect by attacking the zooxanthellae.{{Cite journal |title=Bacterial infection and coral bleaching |journal=Nature |volume=380 |page=396 |year=1996 |doi=10.1038/380396a0 |vauthors=Kushmaro A, Loya Y, Fine M, Rosenberg E |issue=6573 |bibcode=1996Natur.380..396K |s2cid=31033320 |doi-access=free }}{{Cite journal |last1=Sheridan |first1=Christopher |last2=Kramarsky-Winter |first2=Esti |name-list-style=vanc |title=Diseases in coral aquaculture: causes, implications and preventions |journal=Aquaculture |year=2013 |volume=396 |pages=124–135 |doi=10.1016/j.aquaculture.2013.02.037 |last3=Sweet |first3=Michael |last4=Kushmaro |first4=Ariel |last5=Leal |first5=Miguel Costa |bibcode=2013Aquac.396..124S |s2cid=55637399 }} V. shiloi is infectious only during warm periods. Elevated temperature increases the virulence of V. shiloi, which then become able to adhere to a beta-galactoside-containing receptor in the surface mucus of the host coral.{{Cite journal |vauthors=Rosenberg E, Ben-Haim Y |title=Microbial diseases of corals and global warming |journal=Environmental Microbiology |volume=4 |issue=6 |pages=318–26 |date=June 2002 |pmid=12071977 |doi=10.1046/j.1462-2920.2002.00302.x |bibcode=2002EnvMi...4..318R }}{{Cite journal |vauthors=Sutherland KP, Porter J, Torres C |title=Disease and Immunity in Caribbean and Indo-pacific Zooxanthellate Corals |journal=Marine Ecology Progress Series |volume=266 |pages=273–302 |year=2004 |doi=10.3354/meps266273 |bibcode=2004MEPS..266..273S |doi-access=free }} V. shiloi then penetrates the coral's epidermis, multiplies, and produces both heat-stable and heat-sensitive toxins, which affect zooxanthellae by inhibiting photosynthesis and causing lysis.{{Citation needed|date=May 2021}}

During the summer of 2003, coral reefs in the Mediterranean Sea appeared to gain resistance to the pathogen, and further infection was not observed.{{Cite journal |vauthors=Reshef L, Koren O, Loya Y, Zilber-Rosenberg I, Rosenberg E |title=The coral probiotic hypothesis |journal=Environmental Microbiology |volume=8 |issue=12 |pages=2068–73 |date=December 2006 |pmid=17107548 |doi=10.1111/j.1462-2920.2006.01148.x |bibcode=2006EnvMi...8.2068R |citeseerx=10.1.1.627.6120 }} The main hypothesis for the emerged resistance is the presence of symbiotic communities of protective bacteria living in the corals. The bacterial species capable of lysing V. shiloi had not been identified as of 2011.{{Citation needed|date=May 2021}}

{{Update section|date=April 2022|reason=2022 bleaching}}{{See also|Environmental threats to the Great Barrier Reef}}

The Great Barrier Reef along the coast of Australia experienced bleaching events in 1980, 1982, 1992, 1994, 1998, 2002, 2006, 2016, 2017, 2022 and 2024.{{Cite book |title=Climate Change 2007: impacts, adaptation and vulnerability: contribution of Working Group II to the fourth assessment report of the Intergovernmental Panel on Climate Change |vauthors=Hennessy K, Fitzharris B, Bates BC, Harvey N, Howden M, Hughes L, Salinger J, Warrick R |publisher=Cambridge University Press |year=2007 |isbn=978-0-521-70597-4 |veditors=Parry ML, Canziani OF, Palutikof JP, van der Linden PJ, Hanson CE |location=Cambridge, UK |pages=507–40 |chapter=Ch 11. Australia and New Zealand |access-date=8 July 2009 |chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-chapter11.pdf |archive-url=https://web.archive.org/web/20090310150719/http://www.ipcc.ch/pdf/assessment-report/ar4/wg2/ar4-wg2-chapter11.pdf |archive-date=10 March 2009 |url-status=dead}}{{Cite web |last=Plumer |first=Brad |date=31 March 2016 |title=The unprecedented coral bleaching disaster at the Great Barrier Reef, explained |url=https://www.vox.com/2016/3/30/11332636/great-barrier-reef-coral-bleaching |url-status=live |archive-url=https://web.archive.org/web/20170430034706/https://www.vox.com/2016/3/30/11332636/great-barrier-reef-coral-bleaching |archive-date=30 April 2017 |access-date=13 June 2017 |website=Vox Energy & Environment}}{{Cite web |last1=Cantin |first1=Neal |last2=Gilmour |first2=James |date=23 January 2025 |title=Coral bleaching events |url=https://www.aims.gov.au/research-topics/environmental-issues/coral-bleaching/coral-bleaching-events |access-date=23 January 2025 |website=Australian Institute of Marine Science}} Some locations suffered severe damage, with up to 90% mortality.{{Cite book |last1=Johnson |first1=Johanna E |url=http://www.gbrmpa.gov.au/resources-and-publications/publications/climate-change-and-the-great-barrier-reef-a-vulnerability-assessment |title=Climate change and the Great Barrier Reef: a vulnerability assessment |last2=Marshall |first2=Paul A |publisher=Great Barrier Reef Marine Park Authority |year=2007 |isbn=978-1-876945-61-9 |location=Townsville, Qld. |archive-url=https://web.archive.org/web/20140125180404/http://www.gbrmpa.gov.au/resources-and-publications/publications/climate-change-and-the-great-barrier-reef-a-vulnerability-assessment |archive-date=25 January 2014 |url-status=dead |name-list-style=vanc}} The most widespread and intense events occurred in the summers of 1998 and 2002, with 42% and 54%, respectively, of reefs bleached to some extent, and 18% strongly bleached.{{Cite book |url=http://www.hutten.org/fw/docs/319.pdf |title=Global Climate Change and Coral Bleaching on the Great Barrier Reef |vauthors=Done T, Whetton P, Jones R, Berkelmans R, Lough J, Skirving W, Wooldridge S |publisher=Queensland Government Department of Natural Resources and Mines |year=2003 |isbn=978-0-642-32220-3 |archive-url=https://web.archive.org/web/20110927221700/http://www.hutten.org/fw/docs/319.pdf |archive-date=27 September 2011 |url-status=dead}}{{Cite journal |last1=Berkelmans |first1=Ray |last2=De'ath |first2=Glenn |last3=Kininmonth |first3=Stuart |last4=Skirving |first4=William J. |name-list-style=vanc |year=2004 |title=A comparison of the 1998 and 2002 coral bleaching events on the Great Barrier Reef: spatial correlation, patterns, and predictions |journal=Coral Reefs |volume=23 |issue=1 |pages=74–83 |doi=10.1007/s00338-003-0353-y |s2cid=26415495}} However, coral losses on the reef between 1995 and 2009 were largely offset by growth of new corals.{{Cite journal |vauthors=Osborne K, Dolman AM, Burgess SC, Johns KA |date=March 2011 |title=Disturbance and the dynamics of coral cover on the Great Barrier Reef (1995–2009) |journal=PLOS ONE |volume=6 |issue=3 |pages=e17516 |bibcode=2011PLoSO...617516O |doi=10.1371/journal.pone.0017516 |pmc=3053361 |pmid=21423742 |doi-access=free}} An overall analysis of coral loss found that coral populations on the Great Barrier Reef had declined by 50.7% from 1985 to 2012, but with only about 10% of that decline attributable to bleaching, and the remaining 90% caused about equally by tropical cyclones and by predation by crown-of-thorns starfishes.{{Cite journal |vauthors=De'ath G, Fabricius KE, Sweatman H, Puotinen M |date=October 2012 |title=The 27-year decline of coral cover on the Great Barrier Reef and its causes |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=109 |issue=44 |pages=17995–9 |bibcode=2012PNAS..10917995D |doi=10.1073/pnas.1208909109 |pmc=3497744 |pmid=23027961 |doi-access=free}}

A global mass coral bleaching has been occurring since 2014 because of the highest recorded temperatures plaguing oceans. These temperatures have caused the most severe and widespread coral bleaching ever recorded in the Great Barrier reef. The most severe bleaching in 2016 occurred near Port Douglas. In late November 2016, surveys of 62 reefs showed that long term heat stress from climate change caused a 29% loss of shallow water coral. The highest coral death and reef habitat loss was inshore and mid-shelf reefs around Cape Grenville and Princess Charlotte Bay.Final Report: 2016 Coral Bleaching Event on Great Barrier Reef . Great Barrier Reef Marine Park Authority Townsville, 2017, pp. 24–24, Final Report: 2016 Coral Bleaching Event on Great Barrier Reef .

The IPCC's moderate warming scenarios (B1 to A1T, 2 °C by 2100, IPCC, 2007, Table SPM.3, p. 13{{Cite book |author=IPCC |title=Climate change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press |year=2007 |veditors=Solomon S, Qin D, Manning M, Chen Z, Marquis M, Averyt KB, Tignor M, Miller HL |author-link6=Kristen Averyt|location=Cambridge, UK |pages=1–18 |chapter=Summary for policymakers |access-date=8 July 2009 |chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf |archive-url=https://web.archive.org/web/20170507093020/http://www.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-spm.pdf |archive-date=7 May 2017 |url-status=live}}) forecast that corals on the Great Barrier Reef are very likely to regularly experience summer temperatures high enough to induce bleaching.

A study from early 2024 tracked 462 colonies of corals at One Tree Island after they were affected by heat stress. At the end of the study in July 2024 only 92 coral colonies were unaffected by bleaching, while 193 were dead and 113 were showing signs of bleaching.{{Cite news |last=Readfearn |first=Graham |date=2025-01-21 |title='Catastrophic': Great Barrier Reef hit by its most widespread coral bleaching, study finds |url=https://www.theguardian.com/environment/2025/jan/22/catastrophic-great-barrier-reef-hit-by-its-most-widespread-coral-bleaching-study-finds |access-date=2025-01-23 |work=The Guardian |language=en-GB |issn=0261-3077}}

In 1996, Hawaii's first major coral bleaching occurred in Kaneohe Bay, followed by major bleaching events in the Northwest islands in 2002 and 2004.{{Cite web |title=Climate Change and Marine Disease |url=http://dlnr.hawaii.gov/coralreefs/climate-change-and-marine-disease/ |url-status=live |archive-url=https://web.archive.org/web/20200608181743/https://dlnr.hawaii.gov/coralreefs/climate-change-and-marine-disease/ |archive-date=8 June 2020 |access-date=2019-08-15 |website=dlnr.hawaii.gov |language=en}} In 2014, biologists from the University of Queensland observed the first mass bleaching event, and attributed it to The Blob.{{Cite web |year=2015 |title=Rapidly warming ocean a threat to Hawaiian coral reefs |url=https://www.uq.edu.au/news/article/2015/09/rapidly-warming-ocean-threat-hawaiian-coral-reefs |url-status=live |archive-url=https://web.archive.org/web/20150907021425/http://www.uq.edu.au/news/article/2015/09/rapidly-warming-ocean-threat-hawaiian-coral-reefs |archive-date=7 September 2015 |access-date=3 September 2015 |publisher=The University of Queensland}} In 2014 and 2015, a survey in Hanauma Bay Nature Preserve on Oahu found 47% of the corals suffering from coral bleaching and close to 10% of the corals dying.{{Cite news |title=Corals in peril at a popular Hawaiian tourist destination due to global climate change |url=https://phys.org/news/2017-05-corals-peril-popular-hawaiian-tourist.html#jCp |url-status=live |access-date=30 May 2017 |archive-url=https://web.archive.org/web/20170530161529/https://phys.org/news/2017-05-corals-peril-popular-hawaiian-tourist.html#jCp |archive-date=30 May 2017}} In 2014 and 2015, 56% of the coral reefs of the big island were affected by coral bleaching events. During the same period, 44% of the corals on west Maui were effected.{{Cite web |last=Kahn |first=Brian |date=8 November 2017 |title=Coral Bleaching Has Ravaged Half of Hawaii's Coral Reefs |url=https://earther.gizmodo.com/coral-bleaching-has-ravaged-half-of-hawaiis-reefs-1820259549 |url-status=live |archive-url=https://web.archive.org/web/20181215224150/https://earther.gizmodo.com/coral-bleaching-has-ravaged-half-of-hawaiis-reefs-1820259549 |archive-date=15 December 2018 |access-date=12 December 2018 |website=Gizmodo}} On 24 January 2019, scientists with The Nature Conservancy found that the reefs had begun to stabilize nearly 4 years after the last bleaching event.{{Cite news |date=24 January 2019 |title=Hawaii coral reefs stabilizing following bleaching event |work=Associated Press |url=https://www.apnews.com/3781e1cd10f546a0ad679cf6ed81668c |url-status=live |access-date=25 January 2019 |archive-url=https://web.archive.org/web/20190124224121/https://apnews.com/3781e1cd10f546a0ad679cf6ed81668c |archive-date=24 January 2019}} According to the Division of Aquatic Resources (DAR), there was still a considerable amount of bleaching in 2019. On Oahu and Maui, up to 50% of the coral reefs were bleached. On the big island, roughly 40% of corals experienced bleaching in the Kona coast area. The DAR stated that the recent bleaching events have not been as bad as the 2014–2015 events.{{Cite web |title=11/5/19 – CORAL BLEACHING NOT AS SEVERE AS PREDICTED BUT STILL WIDESPREAD; Extensive Surveys Show Bleaching Event Now Abating |url=https://dlnr.hawaii.gov/blog/2019/11/05/nr19-186/ |url-status=live |archive-url=https://web.archive.org/web/20201129022937/https://dlnr.hawaii.gov/blog/2019/11/05/nr19-186/ |archive-date=29 November 2020 |access-date=2020-12-06 |website=dlnr.hawaii.gov |language=en}} In 2020, the National Oceanic and Atmospheric Administration (NOAA) released the first-ever nationwide coral reef status report. The report stated that the northwestern and main Hawaiian islands were in "fair" shape, meaning the corals have been moderately impacted.{{Cite report |url=https://repository.library.noaa.gov/view/noaa/27295 |title=Coral reef condition: A status report for U.S. coral reefs |last1=Donovan |first1=Caroline |last2=Towle |first2=Erica K. |date=2020 |publisher=Coral Reef Conservation Program, University of Maryland Center for Environmental Science |doi=10.25923/wbbj-t585 |language=en |last3=Kelsey |first3=Heath |last4=Allen |first4=Mary |last5=Barkley |first5=Hannah |last6=Besemer |first6=Nicole |last7=Blondeau |first7=Jeremiah |last8=Eakin |first8=Mark |last9=Edwards |first9=Kimberly |access-date=10 December 2020 |archive-url=https://web.archive.org/web/20201128200725/https://repository.library.noaa.gov/view/noaa/27295 |archive-date=28 November 2020 |url-status=live |first11=Chloe |last11=Fleming |first10=Ian |last10=Enochs}}

• Hawaiian Sunscreen Policy In May 2018, Hawaii passed the bill "SB-2571", banning the vending of sunscreen containing chemicals deemed conducive of coral bleaching on the island's local reefs. The bill was signed in by David Ige, of the Democratic party.{{Cite web |title=Hawaii SB2571 {{!}} 2018 {{!}} Regular Session |url=https://legiscan.com/HI/text/SB2571/id/1788969 |access-date=2022-05-29 |website=LegiScan |language=en}}  A chemical deemed toxic in SB-2571 is the 'oxybenzone' (also banned; octinoxate), a chemical that becomes toxic to coral when exposed to sunlight. Up to one-tenth of the approximated 14,000 tons of sunscreen polluting coral reef areas contains oxybenzone, putting almost half of all coral reefs in danger of being exposed. Coral reefs show increased rates of bleaching in both controlled and natural environments when exposed to high levels of oxybenzone, found in many commercial sunscreen products.{{Cite journal |last1=Downs |first1=C. A. |last2=Kramarsky-Winter |first2=Esti |last3=Segal |first3=Roee |last4=Fauth |first4=John |last5=Knutson |first5=Sean |last6=Bronstein |first6=Omri |last7=Ciner |first7=Frederic R. |last8=Jeger |first8=Rina |last9=Lichtenfeld |first9=Yona |last10=Woodley |first10=Cheryl M. |last11=Pennington |first11=Paul |date=2016-02-01 |title=Toxicopathological Effects of the Sunscreen UV Filter, Oxybenzone (Benzophenone-3), on Coral Planulae and Cultured Primary Cells and Its Environmental Contamination in Hawaii and the U.S. Virgin Islands |url=https://doi.org/10.1007/s00244-015-0227-7 |journal=Archives of Environmental Contamination and Toxicology |language=en |volume=70 |issue=2 |pages=265–288 |doi=10.1007/s00244-015-0227-7 |issn=1432-0703 |pmid=26487337 |bibcode=2016ArECT..70..265D |s2cid=4243494}} Another study showed that over time, the presence of oxybenzone in water will decrease a reef's strength to face other bleaching events such as increasing water temperatures.{{Cite journal |last1=Wijgerde |first1=Tim |last2=van Ballegooijen |first2=Mike |last3=Nijland |first3=Reindert |last4=van der Loos |first4=Luna |last5=Kwadijk |first5=Christiaan |last6=Osinga |first6=Ronald |last7=Murk |first7=Albertinka |last8=Slijkerman |first8=Diana |date=2020-09-01 |title=Adding insult to injury: Effects of chronic oxybenzone exposure and elevated temperature on two reef-building corals |journal=Science of the Total Environment |language=en |volume=733 |pages=139030 |bibcode=2020ScTEn.73339030W |doi=10.1016/j.scitotenv.2020.139030 |issn=0048-9697 |pmid=32446051 |s2cid=218864094|doi-access=free }} SB-2571 banned all sunscreen products with the exception of prescription products. Hawaii is the first U.S. state to introduce this type of ban, which went into effect in January 2021.

Eight severe and two moderate bleaching events occurred between 1960 and 2016 in the coral community in Jarvis Island, with the 2015–16 bleaching displaying the unprecedented severity in the record.{{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 |issn=2399-3642 |pmc=6224388 |pmid=30417118 |hdl=1912/10707}}

About 94% of the corals on Japan's Iriomote Island in the Ryukyu Islands bleached during a significant coral bleaching event that occurred in 2016.{{Cite journal |last1=Nakamura |first1=Masako |last2=Murakami |first2=Tomokazu |last3=Kohno |first3=Hiroyoshi |last4=Mizutani |first4=Akira |last5=Shimokawa |first5=Shinya |date=2022-07-28 |title=Rapid recovery of coral communities from a mass bleaching event in the summer of 2016, observed in Amitori Bay, Iriomote Island, Japan |url=http://dx.doi.org/10.1007/s00227-022-04091-2 |journal=Marine Biology |volume=169 |issue=8 |page=104 |doi=10.1007/s00227-022-04091-2 |pmid=35915766 |bibcode=2022MarBi.169..104N |issn=0025-3162|pmc=9331011 }} Prior to this event, the region typically experienced multiple typhoons during July and August. However, during this particular event, no typhoon was detected until September, suggesting a prolonged period of high seawater temperatures.{{Cite journal |last1=MURAKAMI |first1=Tomokazu |last2=KOHNO |first2=Hiroyoshi |last3=NAKAMURA |first3=Masako |last4=TAMAMURA |first4=Naoya |last5=MIZUTANI |first5=Akira |last6=SHIMOKAWA |first6=Shinya |date=2017 |title=Bleaching in Vertically Distributed Corals in Amitori Bay of Iriomote Island |url=http://dx.doi.org/10.2208/jscejoe.73.i_881 |journal=Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering) |volume=73 |issue=2 |pages=I_881–I_886 |doi=10.2208/jscejoe.73.i_881 |issn=2185-4688}} According to the 2017 Japanese government report, almost 75% of Japan's largest coral reef in Okinawa has died from bleaching.{{Cite news |last=McCurry |first=Justin |date=11 January 2017 |title=Almost 75% of Japan's biggest coral reef has died from bleaching, says report |work=The Guardian |url=https://www.theguardian.com/world/2017/jan/12/almost-75-of-japans-biggest-coral-reef-has-died-from-bleaching-says-report?CMP=share_btn_link |url-status=live |access-date=30 May 2017 |archive-url=https://web.archive.org/web/20170821050354/https://www.theguardian.com/world/2017/jan/12/almost-75-of-japans-biggest-coral-reef-has-died-from-bleaching-says-report?CMP=share_btn_link |archive-date=21 August 2017}}

In summer of 2024, rising sea temperatures were responsible for a major bleaching event that killed 61.2% of corals off Amami-Oshima island, Japan.{{Cite news |last=Kanda |first=Kazuaki |date=3 January 2025 |title=1st big bleaching in 26 years kills 60% of corals off Amami-Oshima |url=https://www.asahi.com/ajw/articles/15552068 |url-status=live |archive-url=https://archive.today/20250109124209/https://www.asahi.com/ajw/articles/15552068 |archive-date=9 January 2025 |access-date=9 January 2025 |work=The Asahi Shimbun}} The bleaching was brought on by sea temperatures 2° higher than in 2023.

Coral reef provinces have been permanently damaged by warm sea temperatures, most severely in the Indian Ocean. Up to 90% of coral cover has been lost in the Maldives, Sri Lanka, Kenya and Tanzania and in the Seychelles during the massive 1997–98 bleaching event. The Indian Ocean in 1998 reported 20% of its coral had died and 80% was bleached. The shallow tropical areas of the Indian Ocean are already experiencing what are predicted to be worldwide ocean conditions in the future. Coral that has survived in the shallow areas of the Indian Ocean may be proper candidates for coral restoration efforts in other areas of the world because they are able to survive the extreme conditions of the ocean.{{Cite journal |last1=Freeman |first1=Lauren A. |last2=Kleypas |first2=Joan A. |last3=Miller |first3=Arthur J. |date=2013-12-05 |title=Coral Reef Habitat Response to Climate Change Scenarios |journal=PLOS ONE |language=en |volume=8 |issue=12 |pages=e82404 |doi=10.1371/journal.pone.0082404 |issn=1932-6203 |pmc=3855618 |pmid=24340025 |bibcode=2013PLoSO...882404F |doi-access=free }}

The Maldives has over 20,000 km² of reefs, of which more than 60% of the coral has suffered from bleaching in 2016.{{Cite journal |last1=Gischler |first1=Eberhard |last2=Storz |first2=David |last3=Schmitt |first3=Dominik |date=April 2014 |title=Sizes, shapes, and patterns of coral reefs in the Maldives, Indian Ocean: the influence of wind, storms, and precipitation on a major tropical carbonate platform |journal=Carbonates and Evaporites |language=en |volume=29 |issue=1 |pages=73–87 |doi=10.1007/s13146-013-0176-z |bibcode=2014CarEv..29...73G |issn=0891-2556 |s2cid=128905096}}{{Cite news |date=8 August 2016 |title=More than 60% of Maldives' coral reefs hit by bleaching |work=The Guardian |url=https://www.theguardian.com/environment/2016/aug/08/more-than-60-of-maldives-coral-reefs-hit-by-bleaching?CMP=share_btn_link |url-status=live |access-date=31 May 2017 |archive-url=https://web.archive.org/web/20180929233301/https://www.theguardian.com/environment/2016/aug/08/more-than-60-of-maldives-coral-reefs-hit-by-bleaching?CMP=share_btn_link |archive-date=29 September 2018}}{{Cite web |date=2016-08-08 |title=Maldives coral reefs under stress from climate change: research survey reveals over 60% of corals bleached {{!}} IUCN |url=https://www.iucn.org/news/secretariat/201608/maldives-coral-reefs-under-stress-climate-change-research-survey-reveals-over-60-corals-bleached |access-date=2024-01-28 |website=www.iucn.org |language=en}} Moreover, the Maldivian coral reef faces risks from the growing tourism industry and coastal construction,{{Cite journal |last1=Brown |first1=Kristen T. |last2=Bender-Champ |first2=Dorothea |last3=Bryant |first3=Dominic E.P. |last4=Dove |first4=Sophie |last5=Hoegh-Guldberg |first5=Ove |date=December 2017 |title=Human activities influence benthic community structure and the composition of the coral-algal interactions in the central Maldives |url=http://dx.doi.org/10.1016/j.jembe.2017.09.006 |journal=Journal of Experimental Marine Biology and Ecology |volume=497 |pages=33–40 |doi=10.1016/j.jembe.2017.09.006 |bibcode=2017JEMBE.497...33B |issn=0022-0981}} as well as land reclamation projects,{{Cite journal |last1=Fallati |first1=Luca |last2=Savini |first2=Alessandra |last3=Sterlacchini |first3=Simone |last4=Galli |first4=Paolo |date=2017-07-26 |title=Land use and land cover (LULC) of the Republic of the Maldives: first national map and LULC change analysis using remote-sensing data |url=http://dx.doi.org/10.1007/s10661-017-6120-2 |journal=Environmental Monitoring and Assessment |volume=189 |issue=8 |page=417 |doi=10.1007/s10661-017-6120-2 |pmid=28748428 |bibcode=2017EMnAs.189..417F |issn=0167-6369}} alongside natural challenges such as diseases.{{Cite journal |last1=Montano |first1=Simone |last2=Giorgi |first2=Aurora |last3=Monti |first3=Matteo |last4=Seveso |first4=Davide |last5=Galli |first5=Paolo |date=2016-05-26 |title=Spatial variability in distribution and prevalence of skeletal eroding band and brown band disease in Faafu Atoll, Maldives |url=http://dx.doi.org/10.1007/s10531-016-1145-3 |journal=Biodiversity and Conservation |volume=25 |issue=9 |pages=1625–1636 |doi=10.1007/s10531-016-1145-3 |bibcode=2016BiCon..25.1625M |issn=0960-3115}}{{Cite journal |last1=Saponari |first1=L. |last2=Dehnert |first2=I. |last3=Galli |first3=P. |last4=Montano |first4=S. |date=2021-03-04 |title=Assessing population collapse of Drupella spp. (Mollusca: Gastropoda) 2 years after a coral bleaching event in the Republic of Maldives |url=http://dx.doi.org/10.1007/s10750-021-04546-5 |journal=Hydrobiologia |volume=848 |issue=11 |pages=2653–2666 |doi=10.1007/s10750-021-04546-5 |bibcode=2021HyBio.848.2653S |issn=0018-8158|hdl=10281/355144 |hdl-access=free }}

Coral reef ecosystems are a notable feature of the western shoreline of the Gulf of Thailand. In 1998 and 2010, there were bleaching events in Thailand; the effects of both occurrences varied among coral species, with some exhibiting more resilience to the 2010 bleaching. In contrast to 1998, there was a more severe bleaching event in 2010.{{Cite journal |last1=Sutthacheep |first1=Makamas |last2=Yucharoen |first2=Mathinee |last3=Klinthong |first3=Wanlaya |last4=Pengsakun |first4=Sittiporn |last5=Sangmanee |first5=Kanwara |last6=Yeemin |first6=Thamasak |date=November 2013 |title=Impacts of the 1998 and 2010 mass coral bleaching events on the Western Gulf of Thailand |url=http://dx.doi.org/10.1016/j.dsr2.2013.04.018 |journal=Deep Sea Research Part II: Topical Studies in Oceanography |volume=96 |pages=25–31 |doi=10.1016/j.dsr2.2013.04.018 |bibcode=2013DSRII..96...25S |issn=0967-0645}} Thailand experienced a severe mass bleaching in 2010 which affected 70% of the coral in the Andaman Sea. Between 30% and 95% of the bleached coral died.{{Cite web |date=25 December 2016 |title=As sea temperatures rise, Thailand sees coral bleeching |url=https://www.pressreader.com/thailand/bangkok-post/20161225/282999694496434 |url-status=live |archive-url=https://web.archive.org/web/20180929233322/https://www.pressreader.com/thailand/bangkok-post/20161225/282999694496434 |archive-date=29 September 2018 |access-date=31 May 2017 |work=Bangkok Post}}

Acropora corals were dominant coral species of Indonesian reef system however they are extremely vulnerable to external stressors. A study was conducted to study effect of mass bleaching event in 2010 on Acropora. Post bleaching recovery is influenced by severity and frequency of the bleaching event.{{Cite journal |last1=Watt-Pringle |first1=Rowan |last2=Smith |first2=David J. |last3=Ambo-Rappe |first3=Rohani |last4=Lamont |first4=Timothy A. C. |last5=Jompa |first5=Jamaluddin |date=2022-06-09 |title=Suppressed recovery of functionally important branching Acropora drives coral community composition changes following mass bleaching in Indonesia |url=http://dx.doi.org/10.1007/s00338-022-02275-2 |journal=Coral Reefs |volume=41 |issue=5 |pages=1337–1350 |doi=10.1007/s00338-022-02275-2 |issn=0722-4028}} Research indicates that frequent moderate disturbances tend to affect Porites, while less frequent but stronger disturbances primarily impact Acropora. Consequently, Acropora demonstrates rapid regrowth in such instances.{{Cite journal |last1=Pratchett |first1=Morgan S. |last2=McWilliam |first2=Michael J. |last3=Riegl |first3=Bernhard |date=2020-04-20 |title=Contrasting shifts in coral assemblages with increasing disturbances |url=http://dx.doi.org/10.1007/s00338-020-01936-4 |journal=Coral Reefs |volume=39 |issue=3 |pages=783–793 |doi=10.1007/s00338-020-01936-4 |issn=0722-4028}}

In 2017, there was a study done on two islands in Indonesia to see how their coral cover was. One of the places was the Melinjo Islands and the other was the Saktu Islands. On Saktu Island, the lifeform conditions were categorized as bad, with an average coral cover of 22.3%. In the Melinjo Islands, the lifeform conditions were categorized as bad, with an average coral cover of 22.2%.

During the 2005 mass bleaching event in Florida, the bleaching patterns varied among species. Colpophyllia natans and Diploria strigosa were particularly susceptible to thermal stress, whereas Stephanocoenia intersepta exhibited greater tolerance. Moreover, it was noted that larger coral colonies experienced more bleaching compared to smaller ones. The prediction suggests that mass bleaching events are likely to affect larger coral colonies even within the same community.{{Cite journal |last=Brandt |first=M. E. |date=2009-09-26 |title=The effect of species and colony size on the bleaching response of reef-building corals in the Florida Keys during the 2005 mass bleaching event |url=http://dx.doi.org/10.1007/s00338-009-0548-y |journal=Coral Reefs |volume=28 |issue=4 |pages=911–924 |doi=10.1007/s00338-009-0548-y |bibcode=2009CorRe..28..911B |issn=0722-4028}}

In South Florida, a 2016 survey of large corals from Key Biscayne to Fort Lauderdale found that about 66% of the corals were dead or reduced to less than half of their live tissue.{{Cite news |last=Fleshler |first=David |date=24 April 2016 |title=South Florida corals dying in "unprecedented" bleaching and disease |work=Sun-Sentinel |url=http://www.sun-sentinel.com/local/fl-coral-dying-20160424-story.html |url-status=live |access-date=30 May 2017 |archive-url=https://web.archive.org/web/20170607152842/http://www.sun-sentinel.com/local/fl-coral-dying-20160424-story.html |archive-date=7 June 2017}}

The first recorded mass bleaching event that took place in the Belize Barrier Reef was in 1998, where sea level temperatures reached up to {{Cvt|31.5|C}} from 10 August to 14 October. For a few days, Hurricane Mitch brought in stormy weather on 27 October but only reduced temperatures by 1 degree or less. During this time period, mass bleaching in the fore-reef and lagoon occurred. While some fore reef colonies suffered some damage, coral mortality in the lagoon was catastrophic.{{Citation needed|date=May 2021}}

The most prevalent coral in the reefs Belize in 1998 was the lettuce coral, Agaricia tenuifolia. On 22 and 23 October, surveys were conducted at two sites and the findings were devastating. Virtually all the living coral was bleached white and their skeletons indicated that they had died recently. At the lagoon floor, complete bleaching was evident among A. tenuifolia. Furthermore, surveys done in 1999 and 2000 showed a near total mortality of A. tenuifolia at all depths. Similar patterns occurred in other coral species as well. Measurements on water turbidity suggest that these mortalities were attributed to rising water temperatures rather than solar radiation.{{Citation needed|date=May 2021}}

Hard coral cover on reefs in the Caribbean have declined by an estimated 80%, from an average of 50% cover in the 1970s to only about 10% cover in the early 2000s.{{Cite journal |vauthors=Smith JE, Brainard R, Carter A, Grillo S, Edwards C, Harris J, Lewis L, Obura D, Rohwer F, Sala E, Vroom PS, Sandin S |date=January 2016 |title=Re-evaluating the health of coral reef communities: baselines and evidence for human impacts across the central Pacific |journal=Proceedings. Biological Sciences |volume=283 |issue=1822 |pages=20151985 |doi=10.1098/rspb.2015.1985 |pmc=4721084 |pmid=26740615}} A 2013 study to follow up on a mass bleaching event in Tobago from 2010 showed that after only one year, the majority of the dominant species declined by about 62% while coral abundance declined by about 50%. However, between 2011 and 2013, coral cover increased for 10 of the 26 dominant species but declined for 5 other populations.{{Cite journal |vauthors=Buglass S, Donner SD, Alemu I JB |date=March 2016 |title=A study on the recovery of Tobago's coral reefs following the 2010 mass bleaching event |journal=Marine Pollution Bulletin |volume=104 |issue=1–2 |pages=198–206 |doi=10.1016/j.marpolbul.2016.01.038 |pmid=26856646 |bibcode=2016MarPB.104..198B |hdl-access=free |hdl=2429/51752}}

Coral in the south Red Sea does not bleach despite summer water temperatures up to {{Cvt|34|C}}.{{Cite web |last=Alevizon |first=William |title=Red Sea Coral Reefs |url=http://www.coral-reef-info.com/red-sea-coral-reefs.html |url-status=dead |archive-url=https://web.archive.org/web/20161206200130/http://www.coral-reef-info.com/red-sea-coral-reefs.html |archive-date=6 December 2016 |access-date=27 February 2014 |website=Coral Reef Facts}}

Coral bleaching in the Red Sea is more common in the northern section of the reefs; the southern part of the reef has been plagued by coral-eating starfish, dynamite fishing and human impacts on the environment. In 1988, there was a massive bleaching event that affected the reefs in Saudi Arabia and Sudan, though the southern reefs were more resilient and it affected them very little. Previously, it was thought that the northern reef suffers more from coral bleaching and shows a fast turnover of coral, while the southern reef was thought to not suffer from bleaching as harshly and show more consistency. However, new research shows that where the southern reef should be bigger and healthier than the northern, it was not. This is believed to be because of major disturbances in recent history from bleaching events, and coral-eating starfish.{{Cite journal |vauthors=Riegl BM, Bruckner AW, Rowlands GP, Purkis SJ, Renaud P |date=31 May 2012 |title=Red Sea coral reef trajectories over 2 decades suggest increasing community homogenization and decline in coral size |journal=PLOS ONE |volume=7 |issue=5 |pages=e38396 |bibcode=2012PLoSO...738396R |doi=10.1371/journal.pone.0038396 |pmc=3365012 |pmid=22693620 |doi-access=free}}

In 2010, coral bleaching occurred in Saudi Arabia and Sudan, where the temperature rose 10 to 11 degrees. Certain taxa experienced 80% to 100% of their colonies bleaching, while some showed on average 20% of that taxa bleaching.{{Cite journal |vauthors=Furby KA, Bouwmeester J, Berumen ML |date=4 January 2013 |title=Susceptibility of central Red Sea corals during a major bleaching event |url=https://scripps.ucsd.edu/biblio/susceptibility-central-red-sea-corals-during-major-bleaching-event |url-status=live |journal=Coral Reefs |volume=32 |issue=2 |pages=505–513 |bibcode=2013CorRe..32..505F |doi=10.1007/s00338-012-0998-5 |archive-url=https://web.archive.org/web/20180929233339/https://scripps.ucsd.edu/biblio/susceptibility-central-red-sea-corals-during-major-bleaching-event |archive-date=29 September 2018 |access-date=29 November 2017 |s2cid=17189231}}

File:The optical feedback loop driving colourful coral bleaching.jpg

In recent times, climate change has been linked to a notable increase in coral mortality. Moreover, mounting evidence suggests that bacteria associated with corals contribute to their ability to withstand thermal stress. Attempts have been undertaken to enhance coral resilience in the face of bleaching incidents.{{Cite journal |last1=Maire |first1=Justin |last2=van Oppen |first2=Madeleine J.H. |date=March 2022 |title=A role for bacterial experimental evolution in coral bleaching mitigation? |url=https://doi.org/10.1016/j.tim.2021.07.006 |journal=Trends in Microbiology |volume=30 |issue=3 |pages=217–228 |doi=10.1016/j.tim.2021.07.006 |pmid=34429226 |issn=0966-842X}} Since corals serve as the fundamental components of coral reefs, their decline significantly affects the endurance and composition of reefs{{Cite journal |last1=Leggat |first1=William P. |last2=Camp |first2=Emma F. |last3=Suggett |first3=David J. |last4=Heron |first4=Scott F. |last5=Fordyce |first5=Alexander J. |last6=Gardner |first6=Stephanie |last7=Deakin |first7=Lachlan |last8=Turner |first8=Michael |last9=Beeching |first9=Levi J. |last10=Kuzhiumparambil |first10=Unnikrishnan |last11=Eakin |first11=C. Mark |last12=Ainsworth |first12=Tracy D. |date=August 2019 |title=Rapid Coral Decay Is Associated with Marine Heatwave Mortality Events on Reefs |url=https://doi.org/10.1016/j.cub.2019.06.077 |journal=Current Biology |volume=29 |issue=16 |pages=2723–2730.e4 |doi=10.1016/j.cub.2019.06.077 |pmid=31402301 |bibcode=2019CBio...29E2723L |issn=0960-9822|hdl=10453/135453 |hdl-access=free }} directly affecting the reef-dwelling organisms.

In 2010, researchers at Penn State discovered corals that were thriving while using an unusual species of symbiotic algae in the warm waters of the Andaman Sea in the Indian Ocean. Normal zooxanthellae cannot withstand temperatures as high as was there, so this finding was unexpected. This gives researchers hope that with rising temperatures due to global warming, coral reefs will develop tolerance for different species of symbiotic algae that are resistant to high temperature, and can live within the reefs.{{Cite web |last=LaJeunesse |first=Todd |title=Diversity of Corals, Algae in Warm Indian Ocean Suggests Resilience to Future Global Warming |url=http://science.psu.edu/news-and-events/2010-news/LaJeunesse2-2010 |publisher=Penn State Science |access-date=27 February 2014 |archive-date=7 March 2014 |archive-url=https://web.archive.org/web/20140307162320/http://science.psu.edu/news-and-events/2010-news/LaJeunesse2-2010 |url-status=live}}{{Cite journal |vauthors=LaJeunesse TC, Smith R, Walther M, Pinzón J, Pettay DT, McGinley M, Aschaffenburg M, Medina-Rosas P, Cupul-Magaña AL, Pérez AL, Reyes-Bonilla H, Warner ME |title=Host-symbiont recombination versus natural selection in the response of coral-dinoflagellate symbioses to environmental disturbance |journal=Proceedings. Biological Sciences |volume=277 |issue=1696 |pages=2925–34 |date=October 2010 |pmid=20444713 |pmc=2982020 |doi=10.1098/rspb.2010.0385 |bibcode=2010RSPSB.277.2925L }}

In 2010, researchers from Stanford University also found corals around the Samoan Islands that experience a drastic temperature increase for about four hours a day during low tide. The corals do not bleach or die regardless of the high heat increase. Studies showed that the corals off the coast of Ofu Island near America Samoa have become trained to withstand the high temperatures. Researchers are now asking a new question: can we condition corals, that are not from this area, in this manner and slowly introduce them to higher temperatures for short periods of time and make them more resilient against rising ocean temperatures.{{Cite web |last1=Climatewire |first1=Lauren Morello |title=Can Corals Adapt to Climate Change and Ocean Acidification? |url=https://www.scientificamerican.com/article/coral-climate-acidification/# |website=Scientific American |access-date=29 November 2017 |archive-date=1 December 2017 |archive-url=https://web.archive.org/web/20171201034054/https://www.scientificamerican.com/article/coral-climate-acidification/ |url-status=live}}

Certain mild bleaching events can cause coral to produce high concentrations of sun-screening pigments in order to shield themselves from further stress.{{Cite journal |last1=Bollati |first1=Elena |last2=D’Angelo |first2=Cecilia |last3=Alderdice |first3=Rachel |last4=Pratchett |first4=Morgan |last5=Ziegler |first5=Maren |last6=Wiedenmann |first6=Jörg |title=Optical Feedback Loop Involving Dinoflagellate Symbiont and Scleractinian Host Drives Colorful Coral Bleaching |journal=Current Biology |date=July 2020 |volume=30 |issue=13 |pages=2433–2445.e3 |doi=10.1016/j.cub.2020.04.055 |pmid=32442463 |doi-access=free|bibcode=2020CBio...30E2433B |hdl=10453/149693 |hdl-access=free }} Some of the pigments produced have pink, blue or purple hues, while others are strongly fluorescent. Production of these pigments by shallow-water corals is stimulated by blue light.{{Cite journal |last1=D’Angelo |first1=Cecilia |last2=Denzel |first2=Andrea |last3=Vogt |first3=Alexander |last4=Matz |first4=Mikhail V. |last5=Oswald |first5=Franz |last6=Salih |first6=Anya |last7=Nienhaus |first7=G. Ulrich |last8=Wiedenmann |first8=Jörg |date=2008-07-29 |title=Blue light regulation of host pigment in reef-building corals |url=https://www.int-res.com/abstracts/meps/v364/p97-106/ |journal=Marine Ecology Progress Series |language=en |volume=364 |pages=97–106 |doi=10.3354/meps07588 |bibcode=2008MEPS..364...97D |issn=0171-8630|doi-access=free }} When corals bleach, blue light inside the coral tissue increases greatly because it is no longer being absorbed by the photosynthetic pigments found inside the symbiotic algae, and is instead reflected by the white coral skeleton.{{Cite journal |last1=Enríquez |first1=Susana |last2=Méndez |first2=Eugenio R. |last3=Iglesias -Prieto |first3=Roberto |date=2005 |title=Multiple scattering on coral skeletons enhances light absorption by symbiotic algae |journal=Limnology and Oceanography |language=en |volume=50 |issue=4 |pages=1025–1032 |doi=10.4319/lo.2005.50.4.1025 |bibcode=2005LimOc..50.1025E |s2cid=27756367 |issn=1939-5590|doi-access=free }} This causes an increase in the production of the sun-screening pigments, making the bleached corals appear very colourful instead of white – a phenomenon sometimes called 'colourful coral bleaching'.

Increased sea surface temperature leads to the thinning of the epidermis and apoptosis of gastrodermis cells in the host coral.{{Cite journal |last1=Baird |first1=Andrew H. |last2=Bhagooli |first2=Ranjeet |last3=Ralph |first3=Peter J. |last4=Takahashi |first4=Shunichi |date=2009-01-01 |title=Coral bleaching: the role of the host |url=https://www.sciencedirect.com/science/article/pii/S0169534708003236 |journal=Trends in Ecology & Evolution |language=en |volume=24 |issue=1 |pages=16–20 |doi=10.1016/j.tree.2008.09.005 |pmid=19022522 |bibcode=2009TEcoE..24...16B |issn=0169-5347}} The reduction in apoptosis and gastrodermis is seen via epithelium, leading to up to a 50% loss in the concentration of symbionts over a short period of time.{{Cite journal |last1=Ainsworth |first1=T. D. |last2=Hoegh-Guldberg |first2=O. |last3=Heron |first3=S. F. |last4=Skirving |first4=W. J. |last5=Leggat |first5=W. |date=2008-10-03 |title=Early cellular changes are indicators of pre-bleaching thermal stress in the coral host |url=https://www.sciencedirect.com/science/article/pii/S0022098108002955 |journal=Journal of Experimental Marine Biology and Ecology |language=en |volume=364 |issue=2 |pages=63–71 |doi=10.1016/j.jembe.2008.06.032 |bibcode=2008JEMBE.364...63A |issn=0022-0981}} Under conditions of high temperature or increased light exposure, the coral will exhibit a stress response that includes producing reactive oxygen species, the accumulation of this if not removed by antioxidant systems will lead to the death of the coral. Studies testing the structures of coral under heat stressed environments show that the thickness of the coral itself greatly decreases under heat stress compared to the control. With the death of the zooxanthellae in the heat stressed events, the coral must find new sources to gather fixed carbon to generate energy, species of coral that can increase their carnivorous tendencies have been found to have an increased likelihood of recovering from bleaching events.{{Cite journal |last1=Grottoli |first1=Andréa G. |last2=Rodrigues |first2=Lisa J. |last3=Palardy |first3=James E. |date=April 2006 |title=Heterotrophic plasticity and resilience in bleached corals |url=https://www.nature.com/articles/nature04565 |journal=Nature |language=en |volume=440 |issue=7088 |pages=1186–1189 |doi=10.1038/nature04565 |pmid=16641995 |bibcode=2006Natur.440.1186G |s2cid=4422247 |issn=1476-4687}}

After the zooxanthellae leaves the coral, the coral structures are often taken over by algae due to their ability to outcompete the zooxanthella since they need less resources to survive.{{Cite journal |last1=McCook |first1=L. |last2=Jompa |first2=J. |last3=Diaz-Pulido |first3=G. |date=2001-05-01 |title=Competition between corals and algae on coral reefs: a review of evidence and mechanisms |url=https://doi.org/10.1007/s003380000129 |journal=Coral Reefs |language=en |volume=19 |issue=4 |pages=400–417 |doi=10.1007/s003380000129 |bibcode=2001CorRe..19..400M |s2cid=19522125 |issn=1432-0975}} There is little evidence of competition between zooxanthellae and algae, but in the absence of zooxanthellae the algae thrives on the coral structures. Once algae takes over and the coral can no longer sustain itself, the structures often begin to decay due to ocean acidification.{{Cite journal |last1=Mollica |first1=Nathaniel R. |last2=Guo |first2=Weifu |last3=Cohen |first3=Anne L. |last4=Huang |first4=Kuo-Fang |last5=Foster |first5=Gavin L. |last6=Donald |first6=Hannah K. |last7=Solow |first7=Andrew R. |date=2018-02-20 |title=Ocean acidification affects coral growth by reducing skeletal density |journal=Proceedings of the National Academy of Sciences |language=en |volume=115 |issue=8 |pages=1754–1759 |doi=10.1073/pnas.1712806115 |issn=0027-8424 |pmc=5828584 |pmid=29378969 |bibcode=2018PNAS..115.1754M |doi-access=free }} Ocean acidification is the process by which carbon dioxide is absorbed into the ocean, this decreases the amounts of carbonate ions in the ocean, a necessary ion corals use to build their skeletons. Corals go through processes of decalcifying and calcifying during different times of the day and year due to temperature fluctuations.{{Cite journal |last1=Dove |first1=Sophie G. |last2=Kline |first2=David I. |last3=Pantos |first3=Olga |last4=Angly |first4=Florent E. |last5=Tyson |first5=Gene W. |last6=Hoegh-Guldberg |first6=Ove |date=2013-09-17 |title=Future reef decalcification under a business-as-usual CO 2 emission scenario |journal=Proceedings of the National Academy of Sciences |language=en |volume=110 |issue=38 |pages=15342–15347 |doi=10.1073/pnas.1302701110 |issn=0027-8424 |pmc=3780867 |pmid=24003127 |bibcode=2013PNAS..11015342D |doi-access=free }} Under current IPCC emission pathway scenarios, corals tend to disintegrate, and the winter months with cooler temperatures will not serve ample time for the corals to reform.

In 2020, scientists reported to have evolved 10 clonal strains of a common coral microalgal endosymbionts at elevated temperatures for 4 years, increasing their thermal tolerance for climate resilience. Three of the strains increased the corals' bleaching tolerance after reintroduction into coral host larvae. Their strains and findings may potentially be relevant for the adaptation to and mitigation of climate change and further tests of algal strains in adult colonies across a range of coral species are planned.{{Cite news |title=Scientists successfully develop 'heat resistant' coral to fight bleaching |url=https://phys.org/news/2020-05-scientists-successfully-resistant-coral.html |access-date=12 June 2020 |work=phys.org |language=en}}{{Cite journal |last1=Cornwall |first1=Warren |title=Lab-evolved algae could protect coral reefs |journal=Science |date=13 May 2020 |doi=10.1126/science.abc7842 |s2cid=219408415 }}{{Cite journal |last1=Buerger |first1=P. |last2=Alvarez-Roa |first2=C. |last3=Coppin |first3=C. W. |last4=Pearce |first4=S. L. |last5=Chakravarti |first5=L. J. |last6=Oakeshott |first6=J. G. |last7=Edwards |first7=O. R. |last8=Oppen |first8=M. J. H. van |title=Heat-evolved microalgal symbionts increase coral bleaching tolerance |journal=Science Advances |date=1 May 2020 |volume=6 |issue=20 |pages=eaba2498 |doi=10.1126/sciadv.aba2498 |pmid=32426508 |pmc=7220355 |bibcode=2020SciA....6.2498B |doi-access=free }}

In 2021, researchers demonstrated that probiotics can help coral reefs mitigate heat stress, indicating that such could make them more resilient to climate change and mitigate coral bleaching.{{Cite news |title=Probiotics help lab corals survive deadly heat stress |url=https://www.sciencenews.org/article/probiotics-lab-coral-heat-stress-death-reef-survival-ocean-warming |access-date=22 September 2021 |work=Science News |date=13 August 2021}}{{Cite journal |last1=Santoro |first1=Erika P. |last2=Borges |first2=Ricardo M. |last3=Espinoza |first3=Josh L. |last4=Freire |first4=Marcelo |last5=Messias |first5=Camila S. M. A. |last6=Villela |first6=Helena D. M. |last7=Pereira |first7=Leandro M. |last8=Vilela |first8=Caren L. S. |last9=Rosado |first9=João G. |last10=Cardoso |first10=Pedro M. |last11=Rosado |first11=Phillipe M. |last12=Assis |first12=Juliana M. |last13=Duarte |first13=Gustavo A. S. |last14=Perna |first14=Gabriela |last15=Rosado |first15=Alexandre S. |last16=Macrae |first16=Andrew |last17=Dupont |first17=Christopher L. |last18=Nelson |first18=Karen E. |last19=Sweet |first19=Michael J. |last20=Voolstra |first20=Christian R. |last21=Peixoto |first21=Raquel S. |title=Coral microbiome manipulation elicits metabolic and genetic restructuring to mitigate heat stress and evade mortality |journal=Science Advances |date=August 2021 |volume=7 |issue=33 |pmid=34389536| doi=10.1126/sciadv.abg3088 |pmc=8363143 |bibcode=2021SciA....7.3088S |language=EN}}

After corals experience a bleaching event to increased temperature stress some reefs are able to return to their original, pre-bleaching state.{{Cite journal |vauthors=Ateweberhan M, Feary DA, Keshavmurthy S, Chen A, Schleyer MH, Sheppard CR |title=Climate change impacts on coral reefs: synergies with local effects, possibilities for acclimation, and management implications |journal=Marine Pollution Bulletin |volume=74 |issue=2 |pages=526–39 |date=September 2013 |pmid=23816307 |doi=10.1016/j.marpolbul.2013.06.011 |bibcode=2013MarPB..74..526A }}{{Cite journal |vauthors=Graham NA, Jennings S, MacNeil MA, Mouillot D, Wilson SK |title=Predicting climate-driven regime shifts versus rebound potential in coral reefs |journal=Nature |volume=518 |issue=7537 |pages=94–7 |date=February 2015 |pmid=25607371 |doi=10.1038/nature14140 |bibcode=2015Natur.518...94G |s2cid=4453338 }} Reefs either recover from bleaching, where they are recolonized by zooxanthellae, or they experience a regime shift, where previously flourishing coral reefs are taken over by thick layers of macroalgae.{{Cite journal |last1=Folke |first1=Carl |last2=Carpenter |first2=Steve |last3=Walker |first3=Brian |last4=Scheffer |first4=Marten |last5=Elmqvist |first5=Thomas |last6=Gunderson |first6=Lance |last7=Holling |first7=C.S. |name-list-style=vanc |title=Regime Shifts, Resilience, and Biodiversity in Ecosystem Management |journal=Annual Review of Ecology, Evolution, and Systematics |volume=35 |issue=1 |year=2004 |pages=557–81 |jstor=30034127 |doi=10.1146/annurev.ecolsys.35.021103.105711 |citeseerx=10.1.1.489.8717 }} This inhibits further coral growth because the algae produces antifouling compounds to deter settlement and competes with corals for space and light. As a result, macroalgae forms stable communities that make it difficult for corals to grow again. Reefs will then be more susceptible to other issues, such as declining water quality and removal of herbivore fish, because coral growth is weaker. Discovering what causes reefs to be resilient or recover from bleaching events is of primary importance because it helps inform conservation efforts and protect coral more effectively.

A primary subject of research regarding coral recovery pertains to the idea of super-corals, otherwise referred to as the corals that live and thrive in naturally warmer and more acidic regions and bodies of water. When transplanted to endangered or bleached reefs, their resilience and irradiance can equip the algae to live among the bleached corals. As Emma Camp, a National Geographic Explorer, marine bio-geochemist and an ambassador for Biodiversity for the charity IBEX Earth,{{Cite web |last1=Camp |first1=Emma |title=Scientist description |url=https://explorer-directory.nationalgeographic.org/emma-f-camp |access-date=9 June 2020 |work=National Geographic |archive-date=10 June 2020 |archive-url=https://web.archive.org/web/20200610022205/https://www.nationalgeographic.org/find-explorers/emma-f-camp |url-status=live}} suggests, the super-corals could have the capability to help with the damaged reefs long-term.{{Citation needed|date=June 2021}} While it can take 10 to 15 years to restore damaged and bleached coral reefs,{{Cite web |last=Coffey |first=Donavyn |date=31 January 2019 |title=What Is Coral Bleaching?|url=https://www.livescience.com/64647-coral-bleaching.html |access-date=2020-06-10 |website=livescience.com |language=en |archive-date=3 June 2020 |archive-url=https://web.archive.org/web/20200603175625/https://www.livescience.com/64647-coral-bleaching.html |url-status=live}} the super-corals could have lasting impacts despite climate change as the oceans rise in temperature and gain more acidity. Bolstered by the research of Ruth Gates, Camp has looked into lower oxygen levels and the extreme, unexpected habitats that reefs can be found in across the globe.{{Citation needed|date=June 2021}}

Corals have shown to be resilient to short-term disturbances. Recovery has been shown in after storm disturbance and crown of thorns starfish invasions. Fish species tend to fare better following reef disturbance than coral species as corals show limited recovery and reef fish assemblages have shown little change as a result of short-term disturbances. In contrast, fish assemblages in reefs that experience bleaching exhibit potentially damaging changes. One study by Bellwood et al. notes that while species richness, diversity, and abundance did not change, fish assemblages contained more generalist species and less coral dependent species. Responses to coral bleaching are diverse between reef fish species, based on what resources are affected.{{Cite journal |last1=Baker |first1=Andrew C. |last2=Glynn |first2=Peter W. |last3=Riegl |first3=Bernhard |name-list-style=vanc |date=10 December 2008 |title=Climate change and coral reef bleaching: An ecological assessment of long-term impacts, recovery trends and future outlook |journal=Estuarine, Coastal and Shelf Science |volume=80 |issue=4 |pages=435–471 |doi=10.1016/j.ecss.2008.09.003 |bibcode=2008ECSS...80..435B}} Rising sea temperature and coral bleaching do not directly impact adult fish mortality, but there are many indirect consequences of both. Coral-associated fish populations tend to be in decline due to habitat loss; however, some herbivorous fish populations have seen a drastic increase due to the increase of algae colonization on dead coral. Studies note that better methods are needed to measure the effects of disturbance on the resilience of corals.{{Cite journal |vauthors=Hughes TP, Graham NA, Jackson JB, Mumby PJ, Steneck RS |title=Rising to the challenge of sustaining coral reef resilience |journal=Trends in Ecology & Evolution |volume=25 |issue=11 |pages=633–42 |date=November 2010 |pmid=20800316 |doi=10.1016/j.tree.2010.07.011 |bibcode=2010TEcoE..25..633H }}

File:Pomacentrus moluccensis2.jpg) is a coral-associated species that has been shown to decline dramatically following coral bleaching.{{Cite journal |last1=Bellwood |first1=David R. |last2=Hoey |first2=Andrew S. |last3=Ackerman |first3=John L. |last4=Depczynski |first4=Martial |name-list-style=vanc |title=Coral bleaching, reef fish community phase shifts and the resilience of coral reefs |journal=Global Change Biology |volume=12 |issue=9 |year=2006 |pages=1587–94 |doi=10.1111/j.1365-2486.2006.01204.x |bibcode=2006GCBio..12.1587B |s2cid=86006489 }}]]

Until recently, the factors mediating the recovery of coral reefs from bleaching were not well studied. Research by Graham et al. (2015) studied 21 reefs around Seychelles in the Indo-Pacific in order to document the long-term effects of coral bleaching. After the loss of more than 90% of corals due to bleaching in 1998 around 50% of the reefs recovered and roughly 40% of the reefs experienced regime shifts to macroalgae dominated compositions. After an assessment of factors influencing the probability of recovery, the study identified five major factors: density of juvenile corals, initial structural complexity, water depth, biomass of herbivorous fishes, and nutrient conditions on the reef. Overall, resilience was seen most in coral reef systems that were structurally complex and in deeper water.

The ecological roles and functional groups of species also play a role in the recovery of regime shifting potential in reef systems. Coral reefs are affected by bioeroding, scraping, and grazing fish species. Bioeroding species remove dead corals, scraping species remove algae and sediment to further future growth, grazing species remove algae.{{Cite journal |vauthors=Bellwood DR, Hughes TP, Folke C, Nyström M |title=Confronting the coral reef crisis |journal=Nature |volume=429 |issue= 6994 |pages=827–33 |date=June 2004 |pmid=15215854 |doi=10.1038/nature02691 |bibcode=2004Natur.429..827B |s2cid=404163 }} The presence of each type of species can influence the ability for normal levels of coral recruitment which is an important part of coral recovery. Lowered numbers of grazing species after coral bleaching in the Caribbean has been likened to sea-urchin-dominated systems which do not undergo regime shifts to fleshy macroalgae dominated conditions.

There is always the possibility of unobservable changes, or cryptic losses or resilience, in a coral community's ability to perform ecological processes. These cryptic losses can result in unforeseen regime changes or ecological flips. More detailed methods for determining the health of coral reefs that take into account long-term changes to the coral ecosystems and better-informed conservation policies are necessary to protect coral reefs in the years to come.

Research is being done to help slow down the mortality rate of corals. Worldwide projects are being completed to help replenish and restore the coral reefs. Current coral restoration efforts include microfragmentation, coral farming, and relocation. The population of corals is rapidly declining, so scientists are doing experiments in coral growth and research tanks to help replenish their population. These research tanks mimic the coral reefs natural environment in the ocean. They are growing corals in these tanks to use for their experiments, so no more corals are being harmed or taken from the ocean. They are also transplanting the successfully grown corals from the research tanks and putting them into the areas of the ocean where the reefs are dying out. An experiment is being done in some coral growth and research tanks by Ruth Gates and Madelaine Van Oppen. They are trying to make "super corals" that can withstand some of the environmental factors that the corals are currently dying from. Van Oppen is also working on developing a type of algae that will have a symbiotic relationship with corals and can withstand water temperature fluctuations for long periods of time. This project may be helping to replenish our reefs, but the growing process of corals in research tanks is very time-consuming. It can take at least 10 years for the corals to fully grow and mature enough to where they will be able to breed. Following Ruth Gates' death in October 2018, her team at the Gates Coral Lab at the Hawai'i Institute of Marine Biology continues her research on restoration efforts. Continuing research and restoration efforts at the Gates Coral Lab focuses on the effects of beneficial mutations, genetic variation, and relocation via human assistance on the resilience of coral reefs.Van Oppen, M. J., & Gates, R. D. (2006). Conservation genetics and the resilience of reef‐building corals. Molecular Ecology, 15(13), 3863-3883.Drury C. (2020) Resilience in Reef-Building Corals: The ecological and evolutionary importance of the host response to thermal stress. Molecular Ecology As of 2019, the Gates Coral Lab team determined that large-scale restoration techniques would not be effective; localized efforts to restore coral reefs on an individual basis are tested to be more realistic and effective while research is conducted to determine the best ways to combat coral destruction on a mass scale.Ainsworth TD, CL Hurd, RD Gates, PW Boyd (2019) How do we overcome abrupt degradation of marine ecosystems and meet the challenge of heatwaves and climate extremes? Global Change Biology 26: 343-354 https://doi.org/10.1111/gcb.14901 {{Webarchive|url=https://web.archive.org/web/20210723092508/https://onlinelibrary.wiley.com/doi/10.1111/gcb.14901 |date=23 July 2021 }}

File:Raui (marine protected area) sign, Rarotonga Island, Cook Islands.jpg.]]

Marine Protected Areas (MPAs) are sectioned-off areas of the ocean designated for protection from human activities such as fishing and un-managed tourism. According to NOAA, MPAs currently occupy 26% of U.S. waters.{{Cite web |last=US Department of Commerce |first=National Oceanic and Atmospheric Administration |title=Where are marine protected areas located? |url=https://oceanservice.noaa.gov/facts/mpaloc.html |access-date=2022-05-29 |website=oceanservice.noaa.gov |language=EN-US}} MPAs have been documented to improve and prevent the effects of coral bleaching in the United States. In 2018, research by coral scientists in the Caribbean concluded that areas of the ocean managed/protected by government had improved conditions that coral reefs were able to flourish in. MPAs defend ecosystems from overfishing, which allows multiple species of fish to thrive and deplete seaweed density, making it easier for young coral organisms to grow and increase in population/strength.{{Cite journal |last1=Steneck |first1=Robert S. |last2=Mumby |first2=Peter J. |last3=MacDonald |first3=Chancey |last4=Rasher |first4=Douglas B. |last5=Stoyle |first5=George |date=2018-05-04 |title=Attenuating effects of ecosystem management on coral reefs |journal=Science Advances |language=en |volume=4 |issue=5 |pages=eaao5493 |doi=10.1126/sciadv.aao5493 |issn=2375-2548 |pmc=5942913 |pmid=29750192 |bibcode=2018SciA....4.5493S }} From this study, a 62% increase in coral populations was recorded due to the protection of an MPA. Higher populations of young coral increase the longevity of a reef, as well as its ability to recover from extreme bleaching events.{{Cite web |last=U. of Queensland |date=14 June 2018 |title=Study finds marine protected areas can help coral reefs |url=https://biological-sciences.uq.edu.au/article/2018/07/study-finds-marine-protected-areas-can-help-coral-reefs |access-date=2022-05-29 |website=biological-sciences.uq.edu.au |language=en |archive-date=26 March 2023 |archive-url=https://web.archive.org/web/20230326092826/https://biological-sciences.uq.edu.au/article/2018/07/study-finds-marine-protected-areas-can-help-coral-reefs |url-status=dead }}

There are a number of stressors locally impacting coral bleaching, including sedimentation, continual support of urban development, land change, increased tourism, untreated sewage, and pollution. To illustrate, increased tourism is good for a country, however, it also comes with costs. An example is the Dominican Republic which relies heavily on its coral reefs to attract tourists resulting in increased structural damage, over fishing, nutrient pollution, and an increase in diseases to the coral reefs. As a result, the Dominican Republic has implemented a sustainable management plan for its land and marine areas to regulate ecotourism.{{Cite journal |last1=Good |first1=Alexandra M. |last2=Bahr |first2=Keisha D. |date=2021-02-12 |title=The coral conservation crisis: interacting local and global stressors reduce reef resiliency and create challenges for conservation solutions |journal=SN Applied Sciences |language=en |volume=3 |issue=3 |pages=312 |doi=10.1007/s42452-021-04319-8 |issn=2523-3971 |s2cid=233919638|doi-access=free }}

Coral reefs provide shelter to an estimated quarter of all ocean species.{{Cite web |title=New DNA study suggests coral reef biodiversity is seriously underestimated |url=https://insider.si.edu/2011/11/dna-barcode-survey-suggests-coral-reef-biodiversity-is-seriously-underestimated/ |website=Smithsonian Insider |date=2 November 2011 |access-date=7 March 2018 |archive-date=7 March 2018 |archive-url=https://web.archive.org/web/20180307214226/https://insider.si.edu/2011/11/dna-barcode-survey-suggests-coral-reef-biodiversity-is-seriously-underestimated/ |url-status=live }} Experts estimate that coral reef services are worth up to $1.2 million per hectare which translates to an average of $172 billion per year.{{Cite web |title=What are coral reef services worth? $130,000 to $1.2 million per hectare, per year: experts |url=https://www.eurekalert.org/pub_releases/2009-10/d-wac101509.php |website=EurekAlert! |publisher=American Association for the Advancement of Science (AAAS) | date = 16 October 2009 |access-date=7 March 2018 |archive-date = 7 March 2018 |archive-url=https://web.archive.org/web/20180307082334/https://www.eurekalert.org/pub_releases/2009-10/d-wac101509.php |url-status=live }} The benefits of coral reefs include providing physical structures such as coastal shoreline protection, biotic services within and between ecosystems, biogeochemical services such as maintaining nitrogen levels in the ocean, climate records, and recreational and commercial (tourism) services.{{Cite book |title=Economic valuation and policy priorities for sustainable management of coral reefs |publisher=World Fish Center |location=Sweden |oclc=56538155 |date=c. 2004 }} Coral reefs are one of the best marine ecosystems to use to as a food source. The coral reefs are also the perfect habitat for rare and economically important species of tropical fish, as they provide the perfect area for fish to breed and create nurseries in. If the populations of the fish and corals in the reef are high, then we can use the area as a place to gather food and things with medicinal properties, creating jobs for people who can collect these specimens. The reefs also have cultural importance in specific regions around the world. Additionally, coral reefs bring great economic impact to regions that rely heavily on tourism. A study conducted found that a restoration project in Maui led to a 47% increase in annual visits and an island-wide welfare gain of $2.9 million, averaging to a welfare gain of $26 per resident.{{cite journal |last1=Fezzi |first1=Carlo |last2=Ford |first2=Derek |last3=Oleson |first3=Kirsten |title=The economic value of coral reefs: Climate change impacts and spatial targeting of restoration measures |journal=Ecological Economics |date=January 2023 |volume=203 |url=https://www.sciencedirect.com/science/article/pii/S0921800922002890?casa_token=Rr4l6ZIicWcAAAAA:vvDM9T8AhsNn_LubsyYzBitv8OFkgK-LrVOXkyqKGHFArKY7uht0BDkqUsmTBoA3BMDVZYJ7P9o |access-date=6 May 2025}}

Coral restoration is a common strategy used to combat the problems brought on by global warming; however, while ecological factors are primarily taken into account, efforts need also be made to address social, economic, and governance factors.{{Cite journal |last1=Hein |first1=Margaux Y. |last2=Birtles |first2=Alastair |last3=Willis |first3=Bette L. |last4=Gardiner |first4=Naomi |last5=Beeden |first5=Roger |last6=Marshall |first6=Nadine A. |date=January 2019 |title=Coral restoration: Socio-ecological perspectives of benefits and limitations |url=http://dx.doi.org/10.1016/j.biocon.2018.11.014 |journal=Biological Conservation |volume=229 |pages=14–25 |doi=10.1016/j.biocon.2018.11.014 |bibcode=2019BCons.229...14H |issn=0006-3207}} The rapid growth in advocacy and implementation of intervention measures, such coral restoration, are a result of the intensifying effects of climate change and human pressure on coral reefs. The goal is to preserve the remaining reefs and the functions that they provide to the reef ecosystem.{{Cite journal |last1=Darling |first1=Emily S. |last2=Côté |first2=Isabelle M. |date=2018-03-02 |title=Seeking resilience in marine ecosystems |url=http://dx.doi.org/10.1126/science.aas9852 |journal=Science |volume=359 |issue=6379 |pages=986–987 |doi=10.1126/science.aas9852 |pmid=29496864 |bibcode=2018Sci...359..986D |issn=0036-8075}}

The Paris Agreement has offered reasons for hope by pledging nations worldwide to maintain the rise in global average temperatures significantly below 2°C compared to pre-industrial levels, with concerted endeavors aimed at capping the increase at 1.5°C.{{Cite web |title=Paris Agreement |url=https://unfccc.int/sites/default/files/english_paris_agreement.pdf |access-date=2024-03-22 |website=unfccc.int}} In 2010, the Convention on Biological Diversity's (CBD) Strategic Plan for Biodiversity 2011–2020 created twenty distinct targets for sustainable development for post-2015. Target 10 indicates the goal of minimizing "anthropogenic pressures on coral reefs".{{Cite web |first=Anil |last=Markandya |name-list-style=vanc |title=Benefits and Costs of the Biodiversity Targets for the Post-2015 Development Agenda |url=http://www.copenhagenconsensus.com/sites/default/files/biodiversity_assessment_-_markandya.pdf |date=21 October 2014 |publisher=Copenhagen Consensus Center |access-date=3 March 2018 |archive-date=21 September 2015 |archive-url=https://web.archive.org/web/20150921072732/http://www.copenhagenconsensus.com/sites/default/files/biodiversity_assessment_-_markandya.pdf |url-status=live }} Two programs were looked at, one that reduces coral reef loss by 50% that has a capital cost of $684 million and a recurrent cost of $81 million. The other program reduces coral reef loss by 80 percent and has a capital cost of $1.036 billion with recurring costs of $130 million. CBD acknowledges that they may be underestimating the costs and resources needed to achieve this target due to lack of relevant data but nonetheless, the cost–benefit analysis shows that the benefits outweigh the costs by a great enough amount for both programs (benefit cost ratio of 95.3 and 98.5) that "there is ample scope to increase outlays on coral protection and still achieve a benefit to cost ratio that is well over one".

• Effects of climate change on oceans

{{Reflist}}

• {{Cite book |last1=Watson |first1=Megan E. |chapter=Coral Reefs |editor-last1=Allin |editor-first1=Craig W. |name-list-style=vanc |title=Encyclopedia of environmental issues |volume=1 |pages=[https://archive.org/details/encyclopediaofen0000unse_w2q7/page/317 317–318] |date=2011 |publisher=Salem Press |location=Pasadena, Calif. |isbn=978-1-58765-735-1 |chapter-url-access=registration |chapter-url=https://archive.org/details/encyclopediaofen0000unse_w2q7 |url=https://archive.org/details/encyclopediaofen0000unse_w2q7/page/317 }}

{{Commons category|Coral bleaching}}

• [http://www.reefbase.org/ Global information system on coral reefs.]
• [https://earth.nullschool.net/#current/ocean/surface/currents/overlay=bleaching_alert_area/winkel3 Current global map of bleaching alert areas.]
• {{Cite news |last=Ajasa |first=Amudalat |date=2024-04-15 |title=Corals are bleaching in every corner of the ocean, threatening its web of life |url=https://www.washingtonpost.com/climate-environment/2024/04/15/global-coral-bleaching-ocean-temperatures/ |access-date=2024-04-16 |newspaper=Washington Post |language=en-US |issn=0190-8286}}

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Category:Coral reefs

Category:Effects of climate change