Variações de longo prazo nos atributos das assembleias de peixes em regiões litorâneas de lagos associados ao rio Paraná : influência do nível hidrológico.

Abstract

The natural variability of flow caused by the hydrological cycles in rivers is of paramount importance for the structuring and maintenance of aquatic biota, especially for fish assemblages. In this context, littoral areas play an important role as ecotones to biodiversity. This study aimed to evaluate the influence of variations in the water cycle in the Paraná River on the fish assemblages of three adjacent lakes, two of them permanently connected and another only seasonally connected to the main Paraná River and they are only 8 km far apart. To test the possible relationships between the water level and variations of the attributes of the fish assemblages, fourteen consecutive years of data were used, collected between 2000 and 2013, using seining nets. During this period, the water level of the Paraná River ranged from 200 to 600 cm, with implications on the patterns of species richness and abundance, which were higher in the isolated lake; evenness not showed a clear trend. The lakes presented, overall, low similarity within and between samples along the years, indicating high heterogeneity and low homogenization of these biotypes, with different colonization opportunities likely due to structural differences between lakes. Only two species were abundant in all lakes, but basically all species were small and sedentary, which is a consistent representation of small Characiformes, which depend on the littoral area to complete their life cycles. Not only the flood but also the seasonal drought appeared to be a factor with direct implications on the isolated lake. Therefore, there was a high evident variability in fish assemblage structure of the littoral areas of the lakes, even considering they are very closely located, what makes it difficult to identify general patterns in the taxonomic distribution of fish. However, the colonization of habitats seems to depend on heterogeneity between them and the seasonal variations in the water level.