Bleaching and mortality of reef organisms during a warming event in 1995 on the Caribbean coast of Costa Rica.

Coral reefs at the Caribbean coast of Costa Rica were affected during a bleaching event associated with the 1995 warming of the Western Caribbean. During doldrum weather in late August 1995, reef organisms at Parque Nacional Cahuita were 62% and 7.4% bleached and dead respectively, whilst 67.6% bleached and 8.2% died in the Refugio Nacional de Vida Silvestre Gandoca-Manzanillo. However, Cahuita had the highest mean number of bleached (257 +/- 51.1) and dead (30.5 +/- 5.6) colonies in the surveyed transects, and bleaching was observed down to a depth of 20 m. The most affected species (>10% of dead colonies) were the hydrocoral Millepora complanata and the scleractinian corals Montastraea spp. at Cahuita, and Porites furcata, Porites porites and M. complanata at Gandoca-Manzanillo. Mean seawater temperature was between 30.5 and 31.1 degrees C (0-18 m depth) during four days of observation at the end of August 1995. Coral reefs of the Costa Rican Caribbean coast have shown a rapid decline during the last 20 years due to natural and anthropogenic disturbances. The effect of the 1995 warming added more pressure to the already deteriorated reefs.