Mass mortality of a Caribbean sea urchin: Immediate effects on community metabolism and other herbivores.

The echinoid Diadema antillarum Philippi was an important herbivore in many areas of the Caribbean prior to the mass mortality that eliminated 95-99% of the individuals throughout the Caribbean in 1983-84. Five days after the mass mortality in St. Croix, U.S. Virgin Islands, algal biomass increased by 20% and algal community primary productivity dropped on both a per unit area basis (37% decrease) and per unit algal biomass basis (61% decrease). This accompanied a 50% decrease in the amount of algal biomass removed by herbivores. Concurrent with the changes in the algal community were increases in the rates of grazing by herbivorous fishes, suggesting that exploitative competition for food was occurring between D. antillarum and some herbivorous fish species. These results suggest that D. antillarum has an important role in structuring both the producer and consumer components of Caribbean coral reef ecosystems.