Chronic broadband noise increases the fitness of a freshwater zooplankton

Although there is an increasing interest in the effects of anthropogenic noise on underwater wildlife, most studies focus on marine mammals and fishes while many others taxa of substantial ecological importance are still overlooked. This is the case for zooplankton species which ensure the coupling between primary producers and fishes in pelagic food webs. Here, we measured lifespan, reproduction and mobility of laboratory-raised water fleasDaphnia magna, a widespread freshwater zooplankton species, in response to continuous broadband noise. Surprisingly, we found a significant increase in survival and fecundity, leading to a higher fitness when considering total offspring production and a slight increase in population growth rate, according to the Euler-Lotka equation. Exposed water fleas were found slower than control individuals and we hypothesised that the energy saved from reduced mobility was reallocated to survival and fecundity. Our results can have implications in aquaculture where the acoustic environment receives little attention. Chronic broadband noise can be associated with certain human activities but the consequences on naturalDaphniapopulations might differ as reduced velocity could have negative outcomes when considering competition and predation. Our result highlights for the first time that, despite the absence of a known hearing system, a zooplanktonic crustacean is affected by chronic noise.