SEA-URCHIN BIOEROSION ON CORAL-REEFS - PLACE IN THE CARBONATE BUDGET AND RELEVANT VARIABLES

Two aspects of erosion by sea urchins (Echinoidea) in coral reef habit ats are: the direct passage of reef framework material through the gut and the indirect effects through the weakening of the reef structure. Urchin bioerosion can equal or exceed reef carbonate production. The impact of urchins on reefs depends on three variables: species type, t est size and population density. Large differences in bioerosion by ur chins of the same test size occur between different species. Size diff erences between species in a sea urchin community, as well as size dif ferences within a species along a reef, can be significant. Bioerosion per urchin increases enormously with size. Changes in population dens ity, through time and space, result in significant changes in bioerosi on. It is demonstrated how the interaction of these variables determin es in-situ sea urchin bioerosion.