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

Abstract

Knickzones are originated from basaltic outcroppings, present runs, riffles and pools and are highly influenced by flood pulses, which maintain their natural dynamic. However, the construction of hydroelectric power plants alters or eliminate the dynamism of this area 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 Sapucaí-Mirim River, Southeast Brazil. We sampled four rocky pools connected to the river and three isolated pools, 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 ichthyofauna structure, with higher values of abundance in the rainy season. The species that most contributed to the high dissimilarity between seasons were Knodus moenkhausii (50% of contribution) and Astyanax bockmanni (21%). The former is the most abundant species in the rainy season and the later in the dry season. The alteration between low and high water level occurs frequently in knickzones, as it is a rocky shallow platform in the middle of a river, with floods occurring seasonally or in stochastic short-term periods. This hydrological seasonal dynamic, high limnological variability and complex interactions of different habitats (pools, runs and rapids) explain the particular ichthyofauna structure in such small area. Our results also indicate the potential importance of basaltic knickzones for regional fish diversity conservation, especially due to the imminent threat by intensive hydropower reservoir construction.

Dispersal of fish eggs and larvae in a cascade of small hydropower plants with fish ladders

“…Species presenting such traits have free-flowing eggs and larvae and, therefore, would rely on downstream dispersal to complete their life cycles (Nakatani et al, 2001). A list of species (see Supplementary Material S1 for more details) occurring in the Sapucaí-Mirim River was compiled from previous studies (Freitas-Souza, 2014;Oliveira et al, 2016;Brambilla et al, 2018) to assure that eggs and larvae not identified at the species level still pertained to species with the aforementioned traits, so they could be reliably treated as having free-flowing embryos in the analyses.…”

“…and species from these genera have been identified as migratory in the Upper Paraná Basin (Vono et al, 2002). Previous studies that sampled adult fish in the same area (Freitas-Souza, 2014;Oliveira et al, 2016;Brambilla et al, 2018) have recorded the occurrence of Pimelodus maculatus Lacépède, 1803 (Pimelodidae), Megaleporinus obtusidens (Valenciennes, 1837) and Megaleporinus piavussu (Britski, Birindelli & Garavello, 2012) (Anostomidae) (see Supplementary Material S1 for more details), indicating that the eggs and larvae identified in this study likely belong to these species. The identification of eggs and larvae was performed in this study using only morphologic criteria.…”