Coral bleaching is the process when corals become white due to loss of symbiotic algae and photosynthetic pigments. This loss of pigment can be caused by various stressors, such as changes in temperature, light, or nutrients.[1][2] Bleaching occurs when coral polyps expel the zooxanthellae (dinoflagellates that are commonly referred to as algae) that live inside their tissue, causing the coral to turn white.[1] The zooxanthellae are photosynthetic, and as the water temperature rises, they begin to produce reactive oxygen species.[2] This is toxic to the coral, so the coral expels the zooxanthellae.[2] Since the zooxanthellae produce the majority of coral colouration, the coral tissue becomes transparent, revealing the coral skeleton made of calcium carbonate.[2] Most bleached corals appear bright white, but some are blue, yellow, or pink due to pigment proteins in the coral.[2]
The leading cause of coral bleaching is rising ocean temperatures due to climate change caused by anthropogenic activities.[3] A temperature about 1 °C (or 2 °F) above average can cause bleaching.[3]The ocean takes in a large portion of the carbon dioxide (CO2) emissions produced by human activity. Although this uptake helps regulate global warming, it is also changing the chemistry of the ocean in ways never seen before. [4] Ocean acidification (OA) is the decline in seawater pH caused by absorption of anthropogenic carbon dioxide from the atmosphere. This decrease in seawater pH has a significant effect on marine ecosystems.[5]
According to the United Nations Environment Programme, between 2014 and 2016, the longest recorded global bleaching events killed coral on an unprecedented scale. In 2016, bleaching of coral on the Great Barrier Reef killed 29 to 50 percent of the reef's coral.[6][7][8][9] In 2017, the bleaching extended into the central region of the reef.[10][11] The average interval between bleaching events has halved between 1980 and 2016.[12] The world's most bleaching-tolerant corals can be found in the southern Persian/Arabian Gulf. Some of these corals bleach only when water temperatures exceed ~35 °C.[13][14]
Bleached corals continue to live, but they are more vulnerable to disease and starvation.[15][16] Zooxanthellae provide up to 90 percent of the coral's energy,[2] so corals are deprived of nutrients when zooxanthellae are expelled.[17] Some corals recover[1] if conditions return to normal,[15] and some corals can feed themselves.[15] However, the majority of coral without zooxanthellae starve.[15]
Normally, coral polyps live in an endosymbiotic relationship with zooxanthellae.[18] This relationship is crucial for the health of the coral and the reef,[18] which provide shelter for approximately 25% of all marine life.[19] In this relationship, the coral provides the zooxanthellae with shelter. In return, the zooxanthellae provide compounds that give energy to the coral through photosynthesis.[19] This relationship has allowed coral to survive for at least 210 million years in nutrient-poor environments.[19] Coral bleaching is caused by the breakdown of this relationship.[2]
^ abcUS Department of Commerce, National Oceanic and Atmospheric Administration. "What is coral bleaching?". oceanservice.noaa.gov. Retrieved 13 September 2021.
^ abcdefg"CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES" (PDF). Archived (PDF) from the original on 29 December 2009.
^ ab"Corals and Coral Reefs". Smithsonian Ocean. 30 April 2018. Archived from the original on 18 October 2020. Retrieved 15 August 2019.
^Turley, Carol (September 2011). "Ocean Acidification. A National Strategy to Meet the Challenges of a Changing Ocean: Book Reviews". Fish and Fisheries. 12 (3): 352–354. doi:10.1111/j.1467-2979.2011.00415.x.
^Hall-Spencer, Jason M.; Thorndyke, Mike; Dupont, Sam (October 2015). "Impact of Ocean Acidification on Marine Organisms—Unifying Principles and New Paradigms". Water. 7 (10): 5592–5598. doi:10.3390/w7105592. hdl:10026.1/3897. ISSN 2073-4441.
^"Coral bleaching on Great Barrier Reef worse than expected, surveys show". The Guardian. 29 May 2017. Archived from the original on 29 May 2017. Retrieved 29 May 2017.
^Gilmour, J. P.; Smith, L. D.; Heyward, A. J.; Baird, A. H.; Pratchett, M. S. (2013). "Recovery of an Isolated Coral Reef System Following Severe Disturbance". Science. 340 (6128): 69–71. Bibcode:2013Sci...340...69G. doi:10.1126/science.1232310. PMID 23559247. S2CID 206546394.
^"The United Nations just released a warning that the Great Barrier Reef is dying". The Independent. 3 June 2017. Archived from the original on 9 June 2017. Retrieved 11 June 2017.
^Hughes TP, Kerry JT, Álvarez-Noriega M, Álvarez-Romero JG, Anderson KD, Baird AH, et al. (March 2017). "Global warming and recurrent mass bleaching of corals" (PDF). Nature. 543 (7645): 373–377. Bibcode:2017Natur.543..373H. doi:10.1038/nature21707. hdl:20.500.11937/52828. PMID 28300113. S2CID 205254779. Archived (PDF) from the original on 12 November 2020. Retrieved 12 April 2020.
^"Mass coral bleaching hits the Great Barrier Reef for the second year in a row". USA Today. 13 March 2017. Archived from the original on 13 March 2017. Retrieved 14 March 2017.
^Galimberti, Katy (18 April 2017). "Portion of Great Barrier Reef hit with back-to-back coral bleaching has 'zero prospect for recovery'". AccuWeather.com. Archived from the original on 18 April 2017. Retrieved 18 April 2017. When coral experiences abnormal conditions, it releases an algae called zooxanthellae. The loss of the colorful algae causes the coral to turn white.
^Hughes TP, Anderson KD, Connolly SR, Heron SF, Kerry JT, Lough JM, et al. (January 2018). "Spatial and temporal patterns of mass bleaching of corals in the Anthropocene" (PDF). Science. 359 (6371): 80–83. Bibcode:2018Sci...359...80H. doi:10.1126/science.aan8048. PMID 29302011. S2CID 206661455. Archived (PDF) from the original on 28 April 2019. Retrieved 25 November 2018.
^Shuail, Dawood; Wiedenmann, Jörg; D'Angelo, Cecilia; Baird, Andrew H.; Pratchett, Morgan S.; Riegl, Bernhard; Burt, John A.; Petrov, Peter; Amos, Carl (30 April 2016). "Local bleaching thresholds established by remote sensing techniques vary among reefs with deviating bleaching patterns during the 2012 event in the Arabian/Persian Gulf". Marine Pollution Bulletin. Coral Reefs of Arabia. 105 (2): 654–659. Bibcode:2016MarPB.105..654S. doi:10.1016/j.marpolbul.2016.03.001. ISSN 0025-326X. PMID 26971815. S2CID 37407032.
^Hume, Benjamin C. C.; Voolstra, Christian R.; Arif, Chatchanit; D’Angelo, Cecilia; Burt, John A.; Eyal, Gal; Loya, Yossi; Wiedenmann, Jörg (19 April 2016). "Ancestral genetic diversity associated with the rapid spread of stress-tolerant coral symbionts in response to Holocene climate change". Proceedings of the National Academy of Sciences. 113 (16): 4416–4421. Bibcode:2016PNAS..113.4416H. doi:10.1073/pnas.1601910113. ISSN 0027-8424. PMC 4843444. PMID 27044109.
^ abcd"What is Coral Bleaching and What Causes It – Fight For Our Reef". Australian Marine Conservation Society. Retrieved 13 September 2021.
^"Coral Bleaching". Great Barrier Reef Foundation. Retrieved 13 September 2021.
^Slezak, Michael (6 June 2016). "The Great Barrier Reef: a catastrophe laid bare". The Guardian. ISSN 0261-3077. Retrieved 13 September 2021.
^ abDove SG, Hoegh-Guldberg O (2006). "Coral bleaching can be caused by distress to the coral. The cell physiology of coral bleaching". In Ove Hoegh-Guldberg, Jonathan T. Phinney, William Skirving, Joanie Kleypas (eds.). Coral Reefs and Climate Change: Science and Management. [Washington]: American Geophysical Union. pp. 1–18. ISBN 978-0-87590-359-0.
^ abcZandonella, Catherine (2 November 2016). "When corals met algae: Symbiotic relationship crucial to reef survival dates to the Triassic". Princeton University. Retrieved 13 September 2021.
Coralbleaching is the process when corals become white due to loss of symbiotic algae and photosynthetic pigments. This loss of pigment can be caused...
at risk of bleaching events where polyps expel the zooxanthellae in response to stress such as high water temperature or toxins. Other corals do not rely...
of global climate change. Coralbleaching is also a major threat to all types of coral. Coralbleaching is when the coral expels the zooxanthella that...
heat-sensitive corals to bleach, with especially widespread bleachings in 1998 and 2010. However, reefs that experience a severe bleaching event become...
September 2007. Great Barrier Reef Marine Park Authority. "CoralBleaching and Mass Bleaching Events". Archived from the original on 20 April 2006. Retrieved...
negatively by coralbleaching and increased sea surface temperatures, which in turn leads to coral reef diseases. The first large-scale coralbleaching occurred...
amounts of coral mucous within 18-48 hrs and bleaching of hard corals within 96 hrs. Among the UV filters that result in coralbleaching according to...
Coralbleaching in Oahu has been on the rise since 1996, when Hawaii's first major coralbleaching occurred in Kaneohe Bay, followed by major bleaching...
community levels. MHWs have led to severe biodiversity changes such as coralbleaching, sea star wasting disease, harmful algal blooms, and mass mortality...
temperatures, the Payar Island Marine Park suffered from widespread coralbleaching at a critical level in the second half of 2010. Furthermore, marine...
coral causing it to undergo a process known as coralbleaching. The ocean's acidity is also a factor. Coral is made of calcium carbonate and is dissolved...
coralbleaching in 2016 (during a global coralbleaching event), which killed approximately 80% of corals. This followed a previous extensive coral bleaching...
throughout the area, which can cause coralbleaching. "Minor paling" of some corals has been observed by local CoralBleaching Early Warning Network, a program...
protect coral reefs. CORAL also has a coralbleaching response network using high-resolution satellite images to monitor coral reefs and bleaching events...
scale bleaching events. The Global Coral Reef Monitoring Network (GCRMN) reported in 2021, that the East Asian Seas region, which includes the Coral Triangle...
different types of coral, including Acropora florida, A. gemmifera, A. hyacinthus, A. intermedia, and Pocillopora damicornis. Coralbleaching has been shown...
overfishing, sedimentation and pollution, bleaching, and even tourist-related damage. For 50 percent of Southeast Asia's coral reefs, they are at high or very high...
the coral's life at risk. Coralbleaching is the result of the loss of vital zooxanthellae; any of the stressors can cause bleaching. The corals expel...
effects experienced by corals due to the loss of algal symbionts in response to environmental stress, a phenomenon known as coralbleaching. Species in the genus...
resilience of coral reefs is the biological ability of coral reefs to recover from natural and anthropogenic disturbances such as storms and bleaching episodes...
to understand global coral reef decline. A chief mechanism for widespread reef degradation has been stress-induced coralbleaching caused by unusually...
events of bleaching in 16 of Jamaica's coral reef sites. The hurricanes affected 68 percent of Jamaica's coral reefs and 38 percent of those corals later...
reef to go into a process known as coralbleaching. “Sunscreens cause the rapid and complete bleaching of hard corals, even at extremely low concentrations...
and human assisted relocation. "Super corals" were defined as those that did not bleach during natural bleaching events when sea temperatures were high...
after the bleaching event. 88% of all corals perished as a result of the coralbleaching of 1998. A significant fraction of the dead corals were still...
showed, 91% of coral in the Great Barrier Reef, have experienced some degree of coralbleaching. The reefs that had higher levels of bleaching, often were...
causing the coral to lose color, known as coralbleaching. Environmental conditions such as a rise in water temperature inflict stress on the corals causing...