Effects of the 1982-83 El Nino Event on Tropical, Eastern Pacific Coral Reefs: Disturbance, Recovery and Retrospective Analyses

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The severe 1982-83 ENSO (El Nino Southern Oscillation) event caused historically unprecedented and catastrophic disturbances to the Eastern Pacific coral reefs. In the aftermath of this event, disturbances to the reefs have continued and may have accelerated. Coupled with low coral recruitment, reef recovery could well take many years. The ecological effects and cause(s) of this regional disturbance have been investigated by a team of Latin and North American colleagues and students in Costa Rica, Panama, and Ecuador (Galapagos Islands) from 1983 to 1984 (Smithsonian Institution support) and from 1985 to 1987 (NSF support). This proposal focuses on coral reef recovery, disturbance processes per se, and retrospective analyses to be studied by a multidisciplinary, international team. Secondary or delayed disturbance effects that will be studied are (a) the disruption of biotic barriers allowing predator (Acanthaster planci) entry to coral prey refugia, (b) predator (corallivore) concentration on surviving coral prey, (c) post-El Nino sea urchin bioerosion of damaged reef frames, (d) damselfish colonization of damaged massive corals, and (e) damselfish/sea urchin/corallivore interactions vis-a-vis massive coral survival. Recovery processes will be studied chiefly with respect to the recruitment of calcifying organisms (corals and coralline algae) onto formerly occupied reef surfaces including examiniation of patch size, character of colonists (asexual or sexual propagules), and relative abundances of surrounding species. Retrospective studies (sclerochronology, oxygen and carbon stable isotope analyses, cadmium analysis, and fluorescent banding patterns) will also be performed on coral cores dating back at least to 1601 to provide a long-term record of ENSO disturbances. Since it is likely that major El Nino disturbances are recurring events, such information should provide a firm basis for understanding the processes controlling coral reef development and distribution in the tropical eastern Pacific.