What is the term for the loss of color in corals due to stress?

The term for the loss of color in corals due to stress is coral bleaching. During bleaching, a coral becomes pale or white because it loses many of the microscopic algae living inside its tissues, or because those algae lose their pigments.

These symbiotic algae, commonly called zooxanthellae, normally provide corals with energy-rich products of photosynthesis and help give them much of their color. Stress such as unusually warm seawater can disrupt the relationship. Other triggers include extreme light, changes in salinity, pollution, sedimentation and disease.

Bleaching does not always mean the coral is immediately dead. If conditions improve, corals may regain their algal partners and recover, although prolonged bleaching can cause starvation, reduced growth, reproductive problems and death. The exposed calcium carbonate skeleton makes the coral appear white, but the coral’s living tissue may still be present.

Coral bleaching is different from coral disease. Disease involves a pathogen or disease process, whereas bleaching primarily describes the visible loss of symbiotic algae or their pigments. Large-scale bleaching events can affect reefs across entire regions.