Influence of Habitat on the Impact of Non-Native Fishes on Native Ichthyofauna in a Group of Lakes of the Lower Doce River, Espírito Santo, Southeastern Brazil

The Doce River basin is the largest river system in southeastern Brazil. Over the last century, the Doce River has been undergoing a serious process of degradation, culminating in a huge environmental disaster due to Fundão tailing dam bursting in Mariana (Minas Gerais) and causing severe damage to biodiversity and local human communities. Near its mouth, the Doce River harbors an extensive lake area, with over ninety lakes on coastal lowlands. These lakes are of fluvial origin and connected to each other and to the main Doce River by small tributary streams. In this area, one of the main sources of impact on the fish fauna is the presence of non-native fish species. We compared richness, taxonomic diversity, beta diversity, species composition and proportion of non-native species in lakes and streams, and related these variables to each other and to environmental variables. We used the indicator species index (IndVal) to identify species associated with each type of environment. We used multivariate analyses to test the influence of stream habitat on the fish fauna in streams and Generalized Linear Models (GLMs) to test the influence of distance to lakes on the proportion of non-native species in streams, and the influence of this proportion on total and native fish richness and diversity. The results showed that some non-native species originating from lentic environments have adapted to the lakes and are spread throughout the internal lake system. In streams, there are proportionally fewer non-native fish and their distribution is more fragmented, as some stretches do not provide the conditions for the establishment of some of these species, making them potential refuges for native ichthyofauna. As the streams move away from the lakes, the proportion of non-native species tends to decrease. In streams, the richness and diversity of native species are affected by the proportion of non-native species, but not in lakes. The native vegetation in the landscape showed no potential for reducing the invasion of non-native species. The depth and width of the streams are directly related to the proportion of non-native species within the streams and are structural characteristics that should be considered in strategies for the conservation of the fish fauna.