Fish assemblage structure on a drowned barrier island in the northwestern Gulf of Mexico

We investigated the assemblage structure of fishes associated with different habitats (inshore mud, shell bank, and offshore mud) over a drowned barrier island, Freeport Rocks Bathymetric High, on the inner continental shelf of the northwestern Gulf of Mexico (NW Gulf). Density data from otter trawls were used to examine spatial (habitat and site) and temporal differences in fish assemblage structure using multi- and univariate procedures. Eight species accounted for 69% of the total composition and in order of decreasing abundance included shoal flounder (Syacium gunteri), dwarf sand perch (Diplectrum bivittatum), red snapper (Lutjanus campechanus), least puffer (Sphoeroides parvus), silver seatrout (Cynoscion nothus), largescale lizardfish (Saurida brasiliensis), silver jenny (Eucinostomus gula), and sand seatrout (Cynoscion arenarius). Multivariate results indicated fish assemblage structure differed among habitats (ANOSIM; Global R = 0.190, P < 0.001) and survey dates (ANOSIM; Global R = 0.541, P < 0.001); however, differences among sites were negligible (ANOSIM; Global R = -0.015, P = 0.749). Highest densities of dwarf sand perch and least puffer were found on the shell bank, while densities of shoal flounder, largescale lizardfish, and silver jenny were highest on offshore mud. In addition, smallest sizes and highest densities of six of the eight abundant species were found in July, suggesting an important period for juvenile fishes. Diversity indices also varied relative to habitat with highest Shannon diversity (H') and species richness (S) values for fishes associated with the shell bank. Results of this study highlight the importance of a mosaic of habitat types to fish assemblages on a drowned barrier island in the NW Gulf.