Interactions between Fish and Invertebrates in the Lowland Area of the Sava River following Excessive Change in Hydrological Regime

Abstract

The littoral zones of freshwaters are highly susceptible to extreme hydrological fluctuations caused by climate-induced changes in the water cycle. Disturbances in the hydrology could affect fish assemblages and their trophic interactions with invertebrates, which constitute a large part of fish diets. In 2014 and 2015, the littoral zone of the Sava River (Croatia) was studied to determine the influence of hydrological extremes on (1) fluctuations in environmental drivers and biocoenoses, and (2) the trophic relationships between fish, macroinvertebrates and zooseston, in an attempt to reveal their trophic interactions. Biocoenotic components showed different tolerance to extreme discharge, resulting in remarkable reductions in fish abundance, diversity, biomass, size and, presumably due to dilution, the abundance of zooseston, which is an important food for fish larvae. By contrast, benthic macroinvertebrates did not show significant fluctuations in abundance, but the share of benthic groups of organisms was shifted during high discharge. Gastropods and amphipods were found to be important food sources for fish. The present study helps to highlight the consequences of hydrological disturbances caused by climate change: the enhancement of stressors in riverine littoral habitats and inhabited communities.