A preliminary examination of depth associated spatial variation in fish assemblages on small artificial reefs

Small concrete artificial reef modules (hemisphere-shaped, approximately 1. 3 m diameter, 1 m high) were placed at two sites, eight modules per site. T he sites were in 7 m and 21 m of water, 1.6 km apart, off the coast of sout heast Florida, USA. The reefs were censused monthly for fish over a 19-mont h period. Species, number of fish, and estimated total length of each indiv idual were recorded by divers using SCUBA. After the monthly census, all fi sh were removed from the reefs with a piscicide. A total of 88 species were recorded in the study, with significantly greater diversity on the deep re efs (monthly mean of 7.6 versus 3.0 shallow, P < 0.001, ANOVA). There were also significantly more biomass (calculated from length), and more Large fi sh (>5 cm) on the reefs at 21 m than at 7 m (P < 0.001). There were more sm all fish at the shallow site (P < 0.05). Although it is not clear what vari able(s) associated with the two depths is responsible for the differences, these results highlight the potential differences in artificial reef and am bient environment interactions within a localized area.