Influence of habitat connectivity and seasonality on the ichthyofauna structure of a riverine knickzone

Knickzone areas are originated from basaltic outcroppings, present runs, riffles, and pools and are highly influenced by flood pulses, which maintain its natural dynamic. However, the construction of hydroelectric power plants alters or eliminate this dynamic and can affect the resident fauna that may be dependent on it. The aim of this study was to evaluate the organization of a knickzone’s ichthyofauna considering the influence of seasonality and connectivity of habitats. The study was performed in a knickzone located in the Sapucai-Mirim River, Southeast Brazil. We sampled four rocky pools connected to the river and three isolated, during rainy and dry conditions. The analysis of the two factors (connectivity and seasonality) and of their interaction showed a significant influence only for seasonality on fish structure, with higher values of richness and abundance in rainy season. This ichthyofauna structure differs from that reported in other stretches of Sapucai-Mirim River, in knickzone were sampled 23% of the total fish species richness known for this river and were reported five new species records. Our results indicate the potential importance of basaltic knickzones for regional fish diversity conservation. Further studies and protection strategies of this kind of environment are necessary, especially due to the imminent threat by intensive hydropower reservoir construction.