Predation and the control of the sea urchin Echinometra viridis and fleshyalgae in the patch reefs of Glovers Reef, Belize

The massive reduction in sea urchin Diadema antillarum populations since th e mid-1980s has been associated with large increases in the abundance of fl eshy algae on many Caribbean reefs despite the availability of other sea ur chin and finfish grazers. This study examined the ecology of a grazer livin g sympatrically with D. antillarum, the common and abundant sea urchin Echi nometra viridis. I examined the role that finfish and invertebrate predator s play in controlling the distribution of E. viridis as well as the ability of this sea urchin to control exposed fleshy algae on the patch reefs of t he Clovers Reef Atoll lagoon. I found that the major predators of this sea urchin were Calamus bajonado (jolthead porgy), Balistes vetula and Canthide rmis sufflamen (queen and ocean triggerfish), Lachnolaimus maximus (hogfish ), and a gastropod, probably Cassis madagascariensis. The abundance of E. v iridis is constrained by predation, which restricts E. viridis to cryptic l ocations, such as crevices. Sea urchins bit a smaller percentage of experim ental algal assays than finfish. Finfish herbivory was associated positivel y with patch reef topographic complexity. Unexpectedly, E. viridis abundanc e was positively correlated with fleshy algal abundance, but negatively cor related with the frequency of finfish bites. Predators restrict E. viridis to crevices and therefore reduce their influence on exposed fleshy algae, e ven at moderately high population densities (up to 10 per square meter). Si nce net benthic primary production of coral reefs is most strongly associat ed with herbivory on exposed surfaces, it would appear that E. viridis is u nable to maintain the same production as reefs dominated by D. antillarum.