The Frederiksted Reef System of western St. Croix: a survey of inshore habitats with observations on cross shelf distribution patterns of fish

Coral reefs and inshore areas that comprise the Frederiksted Reef System of western St. Croix, U.S. Virgin Islands, are threatened by a number of anthropogenic impacts. This reef system has previously received little study. Without baseline information it is difficult to assess changes in fish and benthic communities that may result from anthropogenic activities. The objective of this study was to gather descriptive information on the cross-shelf distribution of hard bottom habitats and to examine differences in associated fish assemblages. Along inshore-offshore transects, divers identified four distinct habitat zones: intertidal and shallow subtidal (zone I), inshore low relief (zone II), patch or transitional reef (zone III) and reef crest (zone IV). Fishes were surveyed within each of the four zones using a Roving Diver Survey (RDS) methodology to determine relative abundance, sighting frequency, and species composition of assemblages. Results from comparisons among zones indicate that fish assemblage structure changes markedly across the shelf. Average species richness was significantly different among zones and increased with depth and distance from shore. Cumulative species richness generally increased with depth and distance from shore and was highest in zone IV. More species were observed in zone II than zone III. Assemblage composition also differed substantially among zones, and the cross-shelf distribution pattern was highly variable. It is suggested that for some species these cross-shelf distribution patterns are indicative of important fishhabitat associations occurring within the Frederiksted Reef system.