Fish composition and assemblage structure in the estuarine mixing zone of a tropical estuary: comparisons between the main channel and an adjacent lagoon

Abstract

Spatial patterns of an estuarine habitat used by fish assemblages were determined for a protected adjacent lagoon and two areas of the main estuarine channel in a small tropical estuary. The tested hypotheses are that protected areas in estuarine zones support comparatively higher fish richness and abundance and have more small-sized fishes than the main channel. The lagoon and channel areas had distinct fish assemblage structures. Several abundant species (e.g. Atherinella brasiliensis, Eugerres brasilianus, Geophagus brasiliensis, Achirus lineatus and Centropomus parallelus) were of a smaller size in the lagoon compared with the estuarine channel and probably use the lagoon as nursery grounds. Moreover, some species (e.g. Anchoa tricolor, Anchoa januaria, Gobionellus oceanicus and Poecilia vivipara) were abundant and occurred only in the lagoon, whereas others (e.g. Trinectes paulistanus, Ctenogobius shufeldti and Citharichthys arenaceus) reached their highest abundance in the lagoon and were rarely found in the estuarine channel. Seasonal variation in the fish assemblage structure was not significant, which may be related to dominance of estuarine resident species. We found that the lagoon supported comparatively higher fish richness and abundance compared with the main estuarine channel because of the more sheltered and structured habitat. These results provide a better understanding of the role of adjacent habitats to fish assemblage and an improved basis for estuarine rehabilitation.