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Coral bleaching
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Underwater view of a shallow coral reef off Guam showing widespread coral bleaching, with many corals appearing white and lacking vibrant color.
What causes coral bleaching on the Great Barrier Reef?
A bright orange starfish rests on top of bleached coral in a coral reef, with various fish and yellow coral visible in the background off the coast of Costa Rica. Map of Australia's Great Barrier Reef showing areas most severely affected by coral bleaching in 2016, 2017, and 2020, marked in orange, pink, and purple along the reef's length. An infographic on the right illustrates four stages of coral bleaching: healthy coral with symbiotic algae, coral under stress as algae depart, bleached coral with a white skeleton, and coral death with other algae species encrusting the skeleton. Close-up of coral reef at Apo Reef, Occidental Mindoro, showing large patches of white bleached coral alongside areas of healthy brown coral. World map highlighting the locations of the most endangered coral reefs, shown in pink along tropical and subtropical coastlines. Notable concentrations appear in the Caribbean Sea, eastern coast of Central America, eastern Africa, the Red Sea, South and Southeast Asia, the South Philippine Sea, and around northern Australia and the South Pacific islands. bleached coral seascape
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Chutes d'Ekom - a waterfall on the Nkam river in the rainforest near Melong, in the western highlands of Cameroon in Africa.
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Underwater view of a shallow coral reef off Guam showing widespread coral bleaching, with many corals appearing white and lacking vibrant color.
coral bleaching near the Mariana Islands Coral bleaching in a shallow coral reef off the coast of the Mariana Islands.

Coral bleaching

marine biology
Also known as: bleaching
Written by
John P. Rafferty
John P. Rafferty writes about Earth processes and the environment. He serves currently as the editor of Earth and life sciences, covering climatology, geology, zoology, and other topics that relate to...
John P. Rafferty
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Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
Britannica Editors
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ā€¢History

Coral bleaching, whitening of coral that results from the loss of a coralā€™s symbiotic algae (zooxanthellae) or the degradation of the algaeā€™s photosynthetic pigment. Bleaching is associated with the devastation of coral reefs, which are home to approximately 25 percent of all marine species. Coral bleaching has a variety of causes. It may result from increases in seawater temperature, particularly when associated with elevated levels of solar irradiance (e.g., ultraviolet radiation), or it may be...

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