Coral bleaching is a stress condition in reef corals that involves a breakdown of the symbiotic relationship between corals and unicellular algae (algae). These microscopic plants live within the coral tissue and provide the coral with food for growth and their normal healthy colour.
The symptoms of bleaching include a gradual loss of colour as zooxanthellae are expelled from the coral tissue, sometimes leaving corals bone white.
Coral bleaching can be caused by stressful environmental conditions such as extreme temperature, low salinity, extreme light and various toxins. However, large-scale bleaching episodes are usually associated with unusually high sea temperatures. This relationship has led to the suggestions that coral reefs are showing early signs of stress due to global warming caused by green house gas emissions.
Bleached corals are still alive and can recover fully if the stressful conditions are not too severe or prolonged. However massive coral mortality is a feature of many severe bleaching episodes. The events of 1982/83 and 1998 in particular resulted in wide spread mortality of some coral in some areas. Following milder bleaching events, most coral recover their health, but this may take several months, and can result in lower growth and abnormal reproduction for some time after normal colour has returned.
Information courtesy of Reefbase. Photos courtesy of GBRMPA.
Creating data of coral reefs by image mapping from
satellites
Heron Reef-bleached
bleached Staghorn Coral
unbleached Staghorn Coral
bleached coral
Fluorescent coral is a sign that it is becoming stressed