Extensive ‘Bleaching’ and Death of Reef Corals on the Pacific Coast of Panamá

Recent ‘bleaching’ and death of hermatypic (reef-building) corals has occurred extensively in Pacific Ocean waters of Panamá (Gulf of Chiriquí), near the Panamá-Costa Rica border. All hydrocorals (Millepora spp.) and scleractinian corals (5 genera) have been affected to some degree in the non-upwelling environment of Chiriquí. No other members of the macrobenthos showed signs of stress (lowered activities, morbidity) or reduced abundance. The affected area, including the mainland, nearshore and offshore islands, and adjacent waters, is about 10,000 km2. Further surveys in the Gulf of Chiriquí may reveal even more extensive mortality. This disturbance began in the dry season (January–April 1983), during a period of clear skies, low rainfall, and minimal river drainage. I first observed large, ‘bleached’ coral patches (up to 100 m2 in area) in mid-March, and observations by others indicate that coral ‘bleaching’ occurred in February and possibly as early as mid-January. Normal and ‘bleached’ corals observed in mid-March were ‘bleached’ and dead, respectively, by the end of April, suggesting that the disturbance is protracted. By the end of the dry season, 80 to 95% of all corals in the affected areas were severely ‘bleached’ or dead.