the process whereby coral turns white as a result of losing the microscopic algae (zooxanthellae) that live in coral's tissues, loss caused by exposure to water temperatures 1-2° Celsius higher than the mean averages at the warmest time of year; global warming is one cause of higher temperatures
a phenomenon occurring when corals under stress expel their mutualistic microscopic algae, called zooxanthellae. This results in a severe decrease or even total loss of photosynthetic pigments. Since most reef building corals have white calcium carbonate skeletons, the latter show through the corals' tissue, and the coral reef appears bleached. [JVG
Warming water may affect the natural balance of the marine ecosystem. In the case of coral reefs, warming water may cause bleaching of the living algae followed by death of the coral skeleton. If coral reefs bleach and die, many species will lose valuable spawning grounds and habitat.