Effects of habitat complexity and temporal variation in rocky reef fish communities in the Santos estuary (SP), Brazil

Abstract

Abstract Rampant human activities within estuaries and adjacent areas lead to a significant loss of habitat for many fish species and decreases the quality of the remaining habitats. In this context, we investigated the effects of habitat complexity and temporal variation on the composition and diversity of rocky reef fishes in two coastal islands in southeastern Brazil, namely Ilha do Mato e Ilha das Palmas. We filmed seven independent transects of 400 m2 in each island in each of the four seasons during a year using remotely operated vehicle (ROV). Using the video records and accessories attached to the ROV, we collected information on environmental variables, habitat complexity, species richness, abundance and diversity. Our pooled data showed 13,993 individuals belonging to 56 species, 13 orders and 24 families of marine fish. Nineteen species (34%) occurred in all four seasons. Nine species (16%) were exclusive to spring, seven (12.5%) were exclusive to autumn, three (5.4%) occurred in summer, and only two species (3.5%) were exclusive to winter. Fish assemblages varied according to the habitat complexity. The environmental variables varied between islands and climatic seasons. Numerical abundance and species richness were positively associated with habitat complexity. The interaction between maximum depth and habitat complexity resulted in a greater abundance of individuals. In addition, species richness was negatively correlated to both salinity and maximum depth. However, increasing both variables simultaneously caused an increase in expected richness, due to interaction effects. Trophic diversity was positively correlated with temperature, whilst habitat diversity did not vary with any of the studied independent variables. Furthermore, we found significant differences between Ilha do Mato and Ilha das Palmas in abundance and in richness, which may be due to streams that present re-circulations bordering the latter and that carry organic matter from the Santos estuary. Finally, our non-destructive and non-sacrificial methodology allowed the successful assessment of fish assemblages in different environments and at different times and the description of important patterns, which may be useful for public policies and management.