Spatial Variability of the Coral Reef Fish Assemblages Offshore Broward County, Florida

The inshore environment of Broward County, Florida consists of three coral reef/hard bottom reef tracts, separated by sand substrate, running parallel to the coast in sequentially deeper water. My study was an extensive inventory of the fishes associated with these reef tracts. At quarter nautical mile intervals, for an eighteen nautical-mile coastline section, fishes were censused at western, eastern edges and crests of each of the three reef tracts. On SCUBA, using the Bohnsack-Bannerot point count method, fish abundance, species richness, sizes (TL), and general habitat characteristics were recorded within an imaginary cylinder 15m in diameter extending to the surface. The position of each count site location was recorded by DOPS after each census. During a 4-year period, August 1998 to November 2002, 667 count sites were censused. A total of 86,463 fish belonging to 211 species (S2 families) were recorded. Significant differences (p<0.05, ANOVA, SNK) in total abundance, species richness and biomass were noted among the three reef tracts. There were significantly greater species richness and fish abundance on the offshore reef tract than on the middle tract, which, in turn, had greater richness and abundance than the inshore reef tract (p<0.05, ANOVA, SNK). The offshore reef tract had significantly higher biomass than the inshore reef tract, which, in turn, had significantly higher biomass than the middle reef tract (p<0.05, ANOVA, SNK). These tract-dependent differences may be due to a variety of variables, such as depth, current, refuge, food availability, or other habitat preferences. Differences were also found based on the site (edges or crest) on the reef and location of the reefs (north or south) relative to Port Everglades and Hillsboro Inlet. The count sites within 5 miles south of Port Everglades had lower total abundance and species richness (p<0.05, ANOVA) than the same number of count sites north of the port. Also, south of Port Everglades, the western edge of the reef tracts had greater abundance and richness values than the eastern edge or the crest (p<0.05, ANOVA). North of Port Everglades, the eastern edge predominated in both abundance and richness (p<0.05, ANOVA). The reason(s) for these differences may be linked to topographic variables. In general, at count sites north of Port Everglades, the eastern edges of the reef tracts have a higher amount of vertical relief, and attendant refuge, than at southern count sites. Likewise, although in general the regressions were weak, bottom cover, rugosity and depth were regressed, to some extent, with differences in species richness and abundance. Hillsboro Inlet had similar findings. Count sites within 3.75 miles south of the inlet had lower abundance and species richness (p<0.05, ANOVA) than the same number of sites north of the inlet. This may be due to the effects of effluent transport by the predominantly north-bound current parallel to the coast of Broward County. Juvenile grunts, an important forage base, were significantly higher on the inshore and middle reefs, which did not differ significantly from each other, than the offshore reef. Of immediate management interest, my findings include a surprising scarcity of legal size groupers (2) and snappers (198) over the entire survey area.