Environmental influences on the demersal fish assemblages in the Sepetiba Bay, Brazil

The structure of the demersal fish assemblage in Sepetiba Bay, southeast Brazil (22degrees54'-23degrees04'S, 43degrees34'-44degrees10'W) was described and related to environmental variables. A 3-yr long trawl survey (from July 1993 to June 1996) was conducted using a stratified random sampling strategy at 158 stations. One hundred and seven species of fishes in 80 genera and 44 families were identified. Gerreidae and Ariidae made up 30.5% and 28.6%, and 19.8% and 28.1% of the total number and weight, respectively. Sciaenidae, Engraulididae, Sparidae, and Carangidae were other prominent families. Three assemblages existed in the bay: one inhabited shallow, less saline and less transparent water in the inner zone (depth < 5 m, transparency < 2 m, salinity < 30 psu, and slightly higher temperature); another in the outer zone with the opposite situation (depth > 10 m, transparency > 3 m, salinity > 30 psu, and slightly lower temperature); and a third assemblage in the middle zone likely to prefer average values or show no clear preferences. Most species decreased in abundance over the 3-yr period of study. No seasonal change was detected in the assemblage structure, but many species were rare, indicating high spatial and temporal patchiness. Canonical correlation analyses were used to describe and compare the fish assemblages in the three different habitats. The outer zone had the greatest number of species recorded, lowest abundance, highest diversity and evenness, and was comprised mainly by Cynossion leiarchus, Prionotus punctatus, Anchoa tricolor, Haemulon steindachneri, Diplectrum radiale, Etropus crossotus, and Sphoeraides greeleyi; the inner zone had the lowest number of species recorded but the greatest number of species per sample, highest abundance, lowest diversity and evenness, being comprised mainly by Diapterus rhombeus, Genidens genidens, Cathrops spixii, Chloroschombrus chrysurus, Sciadeichthyes luniscutis, Cetengraulis edentulus, and Archorsargus rhomboidalis, while the third group had the lowest number of species per sample, being comprised by species widely distributed as Gerres aprion, G. genidens, Gerres gula, and Micropogonias furnieri. Depth, followed by transparency and salinity, were the primary factors influencing assemblage distribution.