Non-additive effects of macrophyte cover and turbidity on predator-prey interactions involving an invertivorous fish and different prey types

Habitat complexity, turbidity and prey type availability affect trophic dynamics, and an improved understanding of how these three factors work together could facilitate interpretations of trophic dynamics in environments with regime shifts. We conducted an experiment to cross these three factors, hypothesising that increasing both turbidity and macrophyte cover reduce consumption of Chironomids more than they reduce consumption of Cypridids. Our results did not support our hypothesis, suggesting that the effect of macrophyte cover on predation depends on turbidity. However, the magnitude of this combined effect is the same as that of turbidity alone. Moreover, turbidity affected predation on both prey types similarly. In addition, the effect of macrophyte cover on predation also depended on prey type. We argue that visual and physical refuges may be as effective as shelter, but macrophyte cover may benefit smaller prey items. This may lead to higher predation rates by small-sized fish on invertebrates during periods of low turbidity devoid of macrophyte cover and to similar predation rates on invertebrates during periods of low turbidity and abundant macrophytes, high turbidity and scarce macrophytes or high turbidity and abundant macrophyte cover.