No abstract

During 1983, patchy but extensive mortality of several stony coral species occurred off the Pacific coast of PanamB, associated with loss of their symbiotic zooxanthellae. This disturbance was coincident with the prolonged 1983 E1 Nino warming event. Normally colored colonies receiving bleached colony portions in iso-, allo-and xenografts remained in a healthy state during a 7 mo period. Neither these transplantation experiments, nor histopathological examinations, revealed the presence of an infectious agent which might be responsible for the widespread bleaching, although suspected bacteria were found in electron microscopy preparations of 2 species of bleached corals. The condition of affected coral tissues ranged from slight to severe atrophy and necrosis, but normal-appearing zooxanthellae remained in all but the most necrotic specimens, although reduced in numbers. These observations suggest that environmental (particularly high thermal) stress may have been responsible for the coral deaths.

Coral reefs in the tropical eastern Pacific region experienced catastrophic coral mortality during the severe 1982/1983 El Nino event. Pocillopora spp., the dominant scleractinian reef-building corals, were most seriously affected, resulting in large tracts (0.1 to 1 ha) of dead reef surface in Costa Rica, Panama, Colombia, and the Galapagos Islands, Ecuador. A sea star Acanthaster planci is now entering centrally-located reef areas in Panama corals and is feeding on large, massive corals formerly surrounded and protected by live Pocillopora corals and their symbiotic crustacean guards. This note outlines the effects of El Nifio-related differential coral mortality and subsequent mortality resulting from the elimination of a protective biotic barrier The ages of corals killed during the initial physical disturbance, and later by predation, allow an estimate of the period of uninterrupted reef growth, i.e. the minimum number of years since an earlier, major El Nino event: about 190 yr on the basis of present evidence.