Global threat to Coral Reefs

Coral reefs thrive in the clear, shallow coastal waters of tropical seas. The reefs of southeast Asia-the world's richest-and those in the caribbean have suffered the greatest degradation.

when climatic extremes such as El Nino increase water temperature,symbiotic algae flee the corals' tissue. Without the algae,corals lose their color and a source of energy. Bleached,they may eventually die.

If sediment from storms and coastal development blocks sunlight,corals weaken and become vulnerable to infections such as deadly black band disease.If sewage or agricultural runoff promotes an increase in plankton and a consequent population explosion of crown-of-thorns sea stars.Death comes by predation. Adult sea stars feed mainly on corals.