Assessing the importance of the riparian zone for stream fish communities in a sugarcane dominated landscape (Piracicaba River Basin, Southeast Brazil)

Abstract

In the Neotropics, the effect of agriculture on freshwater habitats is still poorly understood, particularly with respect to sugarcane expansion to meet increased ethanol demands. The variation in taxonomic composition, community attributes and trophic structure of fish assemblages from streams under different riparian zone preservation conditions were studied. Nine stream reaches under the following riparian vegetation conditions were selected: Native Forest (NF), with mostly primary forest; Secondary Forest (SF), which included sites with vegetation in an advanced stage of regeneration surrounded by sugarcane plantations; and Sugarcane sites (SC), located in areas without riparian vegetation, adjacent to sugarcane crops. Forty-one species were collected. The variance partitioning and partial Redundancy Analysis (pRDA) indicated that community composition and trophic structure were significantly explained by riparian condition and spatial variations, while diversity, richness, abundance and biomass were only explained by season and space, with higher diversity and richness at the SF sites. Abundance-Biomass curves (ABC curves) suggested that sugarcane plantations destabilized fish assemblages, especially at the more intensively managed sites, which seem to influence stream integrity and associated fish fauna. We concluded that both physical conditions of streams and some attributes of fish communities reflected the different levels of preservation of the riparian buffers, but given the influence of regional processes which have a pervasive role in shaping local assemblages, land use at the watershed scale seemed to be important especially to explain the higher richness and diversity found at the SF sites.