Diet-specific predation risk cues modulate the functional response of the round goby (Neogobius melanostomus)

Direct predation is a major driver of the negative impact of the invasive round goby Neogobius melanostomus on native macrozoobenthic assemblages. However, the presence of N. melanostomus predators represents a possible means of reducing its negative impact via consumptive and non-consumptive effects (NCEs). However, the NCEs of native predators on the trophic interactions of N. melanostomus remain poorly understood. The functional response framework, which links prey density to the amount of prey consumed, was used to experimentally determine the foraging pressure of N. melanostomus on chironomid larvae and to test how key functional response characteristics, i.e., its shape, attack rate, and handling time, change under predation risk represented by chemical cues from heterospecific or conspecific prey preyed upon by European eel ( Anguilla anguilla ) and enriched with conspecific alarm cues. Predation risk negatively influenced the foraging of N. melanostomus relative to the risk-free control, but the effects differed between heterospecific and conspecific alarm cues. The attack rate and hence the foraging of N. melanostomus at low prey densities were significantly reduced by conspecific alarm cues relative to heterospecific alarm cues and the risk-free control. On the other hand, heterospecific alarm cues led to a longer handling time and consequently a lower maximum feeding rate relative to the risk-free control and conspecific alarm cues. The results show the potential of A. anguilla to reduce the negative impact of the invasive N. melanostomus on benthic prey through NCEs. Thus, ensuring that A. anguilla populations thrive in highly human-impacted, homogenized European freshwater ecosystems represents a promising approach for reducing the negative impact of N. melanostomus on native prey.