CORAL BLEACHING

CORAL BLEACHING Coral bleaching refers to loss of colour of the corals that form the highly fragile ecosystems, coral reefs.
It is a common stress response of corals to various disturbances that occur in the coral reefs which include natural and human-induced events. The natural distur­bances that damage the reefs are violent storms, flooding, temperature extremes, El Nino Southern Oscillation (ENSO) events, subaerial exposures, predatory outbreaks and epi­zoo tics. The human-induced factors like overexploitation, over fishing, increased sedimentation and nutrient overload­ing are responsible for the increased coral reef decline noted. in recent times.

Under stress, the corals expel their zooxanthellae, with whom they have a symbiotic relationship, which leads to their lighter or completely white appearance (as the algae are responsible for the corals' beautiful coloration).
Coral bleaching affects the corals severely. If the bleaching decreases with time, that is, if the stress-causing factors are not too severe, the corals can regain their symbiotic algae in a few weeks or months. They may be then recolonised by the same zooxanthellae species or by a different one. But if the bleaching is severe, the depleted zooxanthellae do not recover and the corals die. The reef itself is then lost.

In an attempt to save coral reefs from bleaching, countries have begun considering development of national strategies. The Great Barrier Reef Marine Park Authority has developed a 'Coral Bleaching Response Plan' to come up with a comprehensive strategy to detect and respond to widespread coral bleaching events during summer. A combined international effort, wide in scope, is the need of the hour.