Patterns of predation on a sea urchin, Echinometra mathaei (de Blainville), on Kenyan coral reefs.

Abstract

Rates and factors affecting predation on the omnivorous burrowing sea urchin Echinometra mathaei (de Blainville) were studied on four Kenyan coral reefs, two with a history of heavy fishing and two protected from fishing. Three hypotheses concerning predation were tested; these were that predation should be lower (1) on fished reefs compared to unfished reefs, (2) in shallower water and therefore between sites within reefs as a function of water depth and (3) with increasing sea urchin body size. Results support the above hypotheses with fishing being the most important variable followed by depth and individual body size. Finfish accounted for 90%, asteroids 5% and gastropods 5% of the predation which suggests that the removal of finfish is more important than shelling in restricting E. mathaei populations. Depth was less important within fished sites than the protected site where very small differences in depth corresponded to increases in predation. Reef flat sites consistently had the lowest predation rates which accounts for E. mathaei natural (unfished) distribution on reef flats.