Marine Influence on Fish Assemblage in Coastal Streams of Itanhaém River Basin, Southeastern Brazil

LEUNG¹, R. & CAMARGO¹, A.F.M.

¹ Departamento de Ecologia and Centro de Aqüicultura, Instituto de Biociências, Universidade Estadual Paulista – UNESP - Av. 24A, 1515. CEP 13506-900, Rio Claro, SP, Brazil. e-mail: rleung@bol.com.br

ABSTRACT: There are many studies of fish community in several estuaries around the world, but there is little information about the influence of marine-estuarine species on the structure of freshwater fish community in coastal streams. Our objective was to study the effect of marine-estuarine species on the structure of freshwater fish assemblage in coastal streams of Itanhaém River basin, Southeastern Brazil. Fishes were sampled with gill nets and dip nets in four sampling sites located 12, 14, 15, and 26 km from the mouth of estuary. Sampled fishes belonged to 19 species and 12 families. Five species were marine-estuarine: Centropomus pectinatus, Dormitator maculatus, Anchoa tricolor, Awaous tajasica, and Syngnathus folletti. The most abundant freshwater species were Hyphessobrycon reticulatus, Geophagus brasiliensis, Characidium lanei, and Phalloceros caudimaculatus. The sampling site closer to the estuary had the highest number of species and the highest abundance of marine-estuarine fishes that corresponded to 33% of species richness and 5% of the individuals. In other sites, marine-estuarine fishes were rare, and had a low contribution to increase species richness and diversity. They corresponded up to 13% of total number of species and 1.3% of total individuals sampled at each site. Their effect on the assemblage structure was qualitative and not quantitative. The abundance of marine-estuarine fishes was positively correlated with salinity and pH, and negatively correlated with the distance to the estuary. The majority of species was euryhaline and would not find any difficulty to enter streams with very low salinity, however most fishes were found next to the estuary. Probably this distribution is related to the fish life histories (catadromous or amphidromous), that keep them more tied to the estuarine environment. Despite the low abundance, predator fish from the estuary could be important in regulating the freshwater food web through top-down control and trophic cascade. Our findings indicate that marine-estuarine fishes play an important role in structuring the fish assemblages by increasing the species richness and the qualitative dissimilarity among sites.

Key-words: estuary, richness, diversity, distribution, similarity, salinity.