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 Nino-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.