From behaviour to complex communities: Resilience to anthropogenic noise in a fish-induced trophic cascade

Sound emissions from human activities represent a pervasive environmental stressor. Individual responses in terms of behaviour, physiology or anatomy are well documented but whether they propagate through nested ecological interactions to alter complex communities needs to be better understood. This is even more relevant for freshwater ecosystems that harbour a disproportionate fraction of biodiversity but receive less attention than marine and terrestrial systems. We conducted a mesocosm investigation to study the effect of chronic exposure to motorboat noise on the dynamics of a freshwater community including phytoplankton, zooplankton, and roach as a planktivorous fish. As expected under the trophic cascade hypothesis, roach predation induced structural changes in the planktonic communities. Surprisingly, although roach changed their feeding behaviour in response to noise, the dynamics of the roach-dominated planktonic communities did not differ between noisy and noiseless mesocosms. This suggests that the top-down structuring influence of roach on planktonic communities might be resilient to noise and reveals the difficulties on extrapolating impacts form individual responses to complex communities.