MOLLUSKAN ZONATION IN A HOLOCENE REEF - CAÑADA HONDA, DOMINICAN REPUBLIC

Five distinct coral facies have been identified in a subaerially exposed Holocene reef in the western Dominican Republic: A. cervicornis, mixed coral, and three distinctive massive-coral units. Surficially exposed mollusks were collected from two1-m² quadrats in each of the five facies along the half-kilometer of outcrop. Additional samples were taken from 0.07-m² quadrats at 40-cm intervals along seven vertical transects.

In a collection of almost 900 mollusks from the ten meter-square quadrats, at least ten genera and twenty species have been identified. Two species, Cerithium litteratum and Lima scabra were found in all 5 of the biozones, and only C. litteratum was found in all quadrats from which samples were collected. (L. scabra was absent from one of the two quadrats in both the uppermost massive coral zone and the A. cervicornis zone). Chama congregata was the most abundant mollusk overall (29%). It dominated in all four quadrats of the two lowermost massive-coral zones (between 30% and 55%), was much less abundant in the mixed coral zone (approximately 4 - 12%), and was all but absent from the uppermost (shallowest?) massive and A. cervicornis zones (0 - 4%).

The data suggest clear trends in the zonation of the molluskan fauna due to water depth, sedimentation rate, and salinity. Subaerial exposure of the Holocene reef system allows us to examine the zonation of mollusks within a reef and explore possible associations between coral and mollusk species. It also reduces bias against attached species that are more difficult to collect from submerged environments.