Small-scale spatial changes in estuarine ¢sh: subtidal assemblages in tropical Brazil

Monthly sampling was conducted during one year in three zones along the estuarine gradient of Ba| ¤ a de Vito ¤ ria, Brazil. Within each zone, unreplicated night trawls were done in deep subtidal £ats located 130^ 210m away and 2^3m deeper than shallow ones.Twenty-one taxa represented 97.5 % of the total mean ¢sh abundance. The taxa Achirus lineatus (meanSD: 20761269 1074 m2), Eucinostomus spp. (694807), Symphurus tessellatus (400626), Sphoeroides testudineus (367597) and Lutjanus synagris (323445) domi-nated the deep assemblage (N36) while Eucinostomus spp. (36494913), A. lineatus (12871569), S. testudineus (12081986), L. synagris (1101927) and Sphoeroides greeleyi (5691404) dominated the shallow assemblage (N35). Taxa exclusive of one or the other depth showed extremely low abundance. The low-salinity shallow £ats showed higher total abundance and taxa number than the high salinity deep locales but richness, diversity and equitability showed no signi¢cant di¡erences among the six stations.The assemblage structure was signi¢cantly correlated to the depth structure but not to physico-chemical char-acteristics of the water. However, the spatial distribution of individual species varied greatly, from depth-dependent pattern to estuarine gradient-dependent pattern, with several intermediates. The community structure is singular in comparison to that of other tropical Brazilian estuaries studied to date. This is probably related to its geographical position in a transitional zone between the northern, tropical Brazilian oceanic domain and the southern, subtropical-temperate domain