Changes in abundance of coral-reef bottom components related to mass mortality of the sea urchin Diadema antillarum

Abstract

The authors have studied the effect of a reduction in grazing pressure, following mass mortalities of the abundant sea urchin Diadema antillarum , on coral-reef bottom components at Curacao (Netherlands Antilles). They surveyed cover of fleshy and filamentous algae, scleractinian corals, crustose coralline algae, loose sediment and a miscellaneous category in permanent quadrats at depths of 27, 15 and 3 m during 1 yr. At all depths, cover of flesh and filamentous algae increased significantly, reaching a new equilibrium. Corals, crustose corallines and/or loose sediment generally decreased in cover, but not all changes were significant. At the species level, they found the coral Agaricia agaricites at 15m, to be relatively vulnerable among corals. The macroalgae Lobophora variegata and Dictyota spp. increased significantly in cover at 27 and 15 m, respectively.They expect, in view of the observed continuously low rates of recruitment of D. antillarum , and in view of the new equilibrium in algal cover, no rapid return to the original situation, unless other herbivorous organisms will take over the role of D. antillarum .