Influence of fish predation on the dynamic of zooplankton and macroinvertebrates in floodplain lakes under different turbidity conditions: an experimental study

Abstract

In alluvial plains, where shallow lakes are subject to inputs of sediments, the impact of turbidity on predator–prey interactions needs to be studied. We conducted an in situ mesocosm study in a shallow floodplain lake during 36 days to evaluate the main and interactive effect of fish predation and turbidity on the abundances, composition and habitat selection of a natural aquatic assemblage, including zooplankton and plant-associated invertebrates, and the cascading effect on phytoplankton biomass. Four treatments were involved: clear water (C), clear water plus fish (CF), turbid water (T), and turbid water plus fish (TF). In each mesocosm, free-floating macrophytes were included to provide environmental heterogeneity, so organisms could display habitat selection. Fish predation was the main factor in structuring the abundances and assemblages composition regardless of turbidity condition. This was explained in part, because turbidity alone did not cause structural changes in the assemblage composition, but produced disorientation of prey organisms, weakening the effect of macrophyte roots as a refuge and favoring the consumption by fish in TF. Therefore, the trophic link between fishes and their prey was the same for zooplankton and stronger for amphipods and chironomids under turbid conditions than in clear waters. Fish caused a cascading effect on phytoplankton biomass, but it was partially counterbalanced under turbid condition due to the negative effect of clay particles on the planktonic algae due to light attenuation. Our results suggest that, within a specific turbidity range, there should be no mismatch in the trophic link between fish and phytoplankton.