Coral bleaching occurs when stony corals turn white.
Stony corals are simple animals that form large reefs. These animals live in a symbiosis with single-celled algae, which expains why the corals live just below sea level. In many cases, photosynthesis by the algae make most of the food products for the coral polyp. Normally, coral polyps live in an endosymbiotic relationship with the algae which is good for the health of the coral and the reef.
Coral polyps are very sensitive to changes in their environment. This includes the temperature of the water they live in. Under stress, coral polyps may expel the algae which live inside their tissues. The algae provide up to 90% of the coral's energy. Bleached corals continue to live but begin to starve after bleaching. Some corals recover.
Above-average sea water temperatures caused by global warming is the leading cause of coral bleaching. 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 between 29 and 50 percent of the reef's coral. In 2017, the bleaching got into the central region of the reef. The average interval between bleaching events has halved between 1980 and 2016.
Recent research showed that the coral-algae relationship is much older than was thought. This suggests it is robust, and has survived many climate changes.
References[change | change source]
- Dove S.G. & Hoegh-Guldberg O. (2006). "Coral bleaching can be caused by stress. The cell physiology of coral bleaching". In Ove Hoegh-Guldberg; et al. (eds.). Coral reefs and climate change: science and management. [Washington]: American Geophysical Union. pp. 1–18. ISBN 0-87590-359-2. Explicit use of et al. in:
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When coral experiences abnormal conditions, it releases an algae called zooxanthellae. The loss of the colorful algae causes the coral to turn white.
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- Halton, Mary 2018. Coral reefs 'weathered dinosaur extinction'. BBC News Science & Environment.