Fish Assemblages on a Mitigation Boulder Reef and Neighboring Hardbottom
Abstract We compared the fish assemblages on a mitigation site to neighboring natural habitat. Artificial reefs made of limestone boulders were deployed offshore Florida in August–September 2003 as mitigation for an anticipated nearshore hardbottom burial associated with a planned beach nourishment. Boulders comprising a footprint of 36,017 m2 were deployed on sand substrate, adjacent to hardbottom, to replace an expected covering of 30,756 m2 hardbottom. Nourishment of the beach was initiated May 2005 and completed in February 2006. Fishes on the artificial mitigation reefs and neighboring natural hardbottom were counted annually in August, 2004 through 2008, with 30-m belt transects and rover-diver surveys. Across all surveys a total of 18,313 fish of 185 species was counted. Mean species richness and abundance were typically greater on the transects at mitigation reefs than on nearshore hardbottom (NHB). MDS plots of Bray–Curtis similarity indices show a clear distinction between the mitigation reefs and NHB fish assemblages regardless if the data were, or were not, standardized to account for rugosity differences. SIMPER analysis indicated the two assemblages had, on average, 75% dissimilarity. Thus, while the mitigation boulders exhibited greater abundance and species richness than the NHB, the two assemblages differed dramatically in structure. The mitigation reefs provided a habitat suitable for fish colonization. However, this habitat differed dramatically in size and appearance from impacted NHB and created a unique environment unlike the NHB. Thus, mitigation reefs in general, and boulder reefs specifically, should not be relied upon to provide an equitable replacement to NHB habitat loss.