Coral Bleaching and Mortality Associated with the 1997-98 El Nino in an Upwelling Environment in the Eastern Pacific (Gulf of Papagayo, Costa Rica)

Abstract

Coincidental with the 1997–98 El Niño, overall coral bleaching (32.4% of all colonies) and mortality (5.7%) were observed on the Pacific coast of Costa Rica, in the seasonally cool waters of the Gulf of Papagayo and in the more thermally stable waters of Golfo Dulce. At a Pavona clavus reef (Culebra Bay, Gulf of Papagayo), mean seawater temperature at 7 m depth ranged from 0.2º to 3.9ºC warmer than in previous years for nearly all months during 1997 and 1998. Water column temperature to 25–30 m depth was above 29ºC for several days, which exceeded the long term average. Even though mortality was low for most coral species, it was severe (>90% decrease in live cover) in a small population of Leptoseris papyracea known only at Culebra Bay. Pocillopora spp. accounted for more than 60% and 80% of all bleached and dead colonies, respectively. Other coral species regained their normal pigmentation by the beginning of 1998 with little evidence of tissue mortality. The El Niño event of 1997–98 is considered the strongest on record by some measures, but coral mortality on the Pacific coast of Costa Rica was much less than in previous events, drawing attention to El Niño disturbance variability on local scales.