Ecological and socioeconomic impacts of 1998 coral mortality in the Indian Ocean: an ENSO impact and a warning of future change?

The year 1998, was the warmest year since the start of temperature recordings some 150 years ago. Similarly, the 1990s have been the warmest decade recorded. In addition, 1998 saw the strongest El Nino ever recorded. As a consequence of this, very high water temperatures were observed in many parts of the oceans, particularly in the tropical Indian Ocean, often with temperatures of 30 to 50C above normal. Many corals in this region bleached and subsequently died, probably due to the high water temperatures in combination with meteorological and climatic factors. Massive mortality occurred on the reefs of Sri Lanka, Maldives, India, Kenya, Tanzania, and Seychelles with mortalities of up to 90% in many shallow areas. Reefs in other parts of the Indian Ocean, or in waters below 20 m, coral mortality was typically 50%. Hence, coral death during 1998 was unprecedented in severity. The secondary socioeconomic effects of coral bleaching for coastal communities of the Indian Ocean are likely to be long lasting and severe. In addition to potential decreases in fish stocks and negative effects on tourism, erosion may become an acute problem, particularly in the Maldives and Seychelles. If the observed global trends in temperature rises continue, there will be an increased probability of a recurrence of the phenomenon observed in 1998 on the coral reefs of the Indian Ocean, as well as in other parts of the tropical oceans in coming years. Coral reefs of the Indian Ocean may prove to be an important signal of the potential effects of global climate change, and we should heed that warning.