Bleaching and recovery of five eastern pacific corals in an El Niño-related temperature experiment

Coral bleaching events have increased in frequency and severity, due mainly to elevated water temperature associated with El Niño-related warming and a general global warming trend. We experimentally tested the effects of El Niño-like sea temperature conditions on five reef-building corals in the Gulf of Panama. Branching species (Pocillopora damicornis and Pocillopora elegans) and massive species (Porites lobata, Pavona clavus and Pavona gigantea) were exposed to experimentally elevated seawater temperature, ∼1-2°C above ambient. Differences in zooxanthellate coral responses to bleaching and ability to recover were compared and quantified. All corals exposed to high temperature treatment exhibited significant declines in zooxanthellae densities and chlorophyll a concentrations. Pocilloporid species were the most sensitive, being the first to bleach, and suffered the highest mortality (50% after 50 d exposure). Massive coral species demonstrated varying tolerances, but were generally less affected. P. gigantea exhibited the greatest resistance to bleaching, with no lethal effects observed. Maximum experimental recovery was observed in P. lobata. No signs of recovery occurred in P. clavus, as zooxanthellae densities and chlorophyll a concentrations continued to decline under ambient (control) conditions. Experimental coral responses from populations in an upwelling environment are contrasted with field responses observed in a nonupwelling area during the 1997-98 El Niño-Southern Oscillation event.