Coral reef degradation in the Indian Ocean. Status reports and project presentation 2000.

Abstract

The temperatures of the world’s oceans are increasing at an accelerating rate. Recent estimates indicate that the magnitude of these increases might be as much as several degrees over the next century and undoubtedly, the impacts of these changes on the Earth’s ecosystems are likely to become increasingly obvious. Coral reefs have already shown dramatic responses to the increasing ocean temperatures. Under normal temperature conditions, reef-building corals, which form the foundation of coral reefs, are living very near the maximum sea temperatures that they can tolerate. If they are exposed to even modest increases in sea temperatures, perhaps only 1° C - 2° C, they become stressed and often ‘bleach’. This bleaching of corals is a response to stress, and it occurs when the symbiotic unicellular algae (zooxanthellae) that lives within the tissues of the coral polyp, are expelled or lost. The coral can survive for short periods without these zooxanthellae but unless the stress that caused the bleaching subsides and new zooxanthellae are incorporated into the tissue of the coral, the coral will die. For several months in early 1998, the temperature of surface waters (< 10 m) over much of the world’s tropical oceans increased between 3° C and 5° C. As a result, corals on reefs throughout the world bleached and, unfortunately, many died. The mortality of corals was particularly serious in the central and western Indian Ocean, where as many as 50% to 95% of all corals died.