Environmental factors structuring the assemblage of aquatic insects in an epigean and hypogean stretch of a Neotropical karst stream

Abstract

The aim of the present study was to identify which variables structure the assemblage of aquatic insects in the subterranean environment, because knowledge about how subterranean communities are structured in rivers with hypogean sections is still emerging. In addition to identifying whether the hypogean assemblage is structured in the same way as the epigean assemblage, we sought to identify whether the environmental restrictions caused by the subterranean habitat resulted in reduced species richness and abundance compared with the epigean habitat. We sampled a 345-m stretch of a stream in Brazil and collected aquatic insects from both the epigean and hypogean environments. In the stream stretch investigated, there was a positive relationship between richness and the percentage of immersion, fine substrate and organic matter, and a negative relationship between richness and conductivity. We also verified differences between the epigean and hypogean environments regarding composition. The variables that best explained the overall assemblage structure included the epigean–hypogean environment and the percentage of coarse and fine substrate. Given the differences between these environments, we emphasise the need for management actions in karst regions that consider the discontinuity of these regions’ river communities to conserve all components of diversity.