Coral Bleaching
A stress response in which corals expel the colorful algae living in their tissue, turning white and becoming vulnerable to starvation.
Definition
Coral bleaching occurs when corals, stressed primarily by unusually warm water, expel the symbiotic algae (zooxanthellae) that live in their tissue and provide most of their food and color. Without these algae, coral tissue turns pale or white and the coral becomes significantly more vulnerable to disease and starvation.
Bleached coral is not necessarily dead -- if water temperatures return to normal quickly enough, corals can recover and regain their algae. But prolonged or repeated bleaching events, increasingly common as ocean temperatures rise, can kill entire reef systems.
In Practice
A marine heatwave that raises ocean temperatures even a few degrees above normal for several weeks can trigger mass coral bleaching across an entire reef system.