Homogenization of Fish Composition Among Mesohabitats Driven by Stream Degradation from Urban Land Use

Abstract

The heterogeneity along the course of streams beget habitat features that are highly different and strongly influence the composition of fish assemblages. Stream stretches such as riffles, runs, and pools are particularly distinct in physical structures and water flow, with expected differences in the identity and body shape of the species that occupy these habitat units. However, how land is used in the adjacent areas of these aquatic environments also changes the habitat characteristics and, therefore, the fish composition from each stretch. In this context, we collected data from both rural and urban streams to assess how these land-use types influence the species composition and their body morphology among mesohabitats. Differences in body morphology were evaluated using Analysis of Variance (ANOVA) on the mean of Compression Index (CI) weighted by the species abundance for each sampled site. The differences in species composition were assessed using permutational multivariate analogous (PERMANOVA) and Indicator Value (IndVal). Urban streams showed a significantly decreased fish diversity combined with no differences in body morphology of fish and homogenization of species composition among mesohabitats. Importantly, we could infer that mesohabitats influence the body shape of fish and, consequently, species composition in less disturbed streams. However, the lower fish diversity in more imperiled streams led to the homogenization of fish composition among mesohabitats. These patterns constitute important contributions for evidence-based management and restoration of streams, as the presence of different mesohabitats is not enough to overcome the effects of urbanization on fish assemblages.