Chronic broadband noise increases the fitness of a freshwater zooplankton

Abstract

Although there is an increasing interest in the effects of anthropogenic noise on animals, aquatic studies mainly focus on organisms with hearing systems (marine mammals, fish, great arthropods) while many others of substantial ecological importance are not considered. Here we show that the water flea Daphnia magna, a widespread zooplankton species serving as food source for higher trophic levels, could be affected by noise pollution in a way that we did not expect. We found that isolated individuals exposed to a continuous broadband sound have a higher survival and fecundity, thus a higher fitness. We also found that they are slower than individuals not exposed to additional noise. It could be that the energy saved from reduced mobility is reallocated to fitness. In natural systems, this reduced velocity should result in a more negative outcome for Daphnia's fitness due to competition and predation. Our result highlights that, despite the absence of a known hearing system, a small crustacean can be affected by noise. Consequently, anthropogenic noise can not only affect communities through top-down cascading effects, when it changes the behaviour of top-predators like fish, but also via bottom-up effects with alterations in zooplankton.

No evidence for an effect of chronic boat noise on the fitness of reared water fleas

“…We did not observe any effect of chronic boat noise exposition on Daphnia magna fecundity or survival. These results are opposite to Prosnier et al’s one (2022), where an exposition to a continuous broadband noise leads to a surprising increase of individuals’ fitness. This contradiction suggested that the effect of chronic noise pollution, on zooplankton species, could depend on the structure of noise.…”

“…For the smaller organisms, like zooplankton, little is known about the important of sound pattern. Here, the comparison with Lara & Vasconcelos (2021) and Prosnier et al (2022) suggest that patterns should also be considered in understanding the noise effects, with higher effect with a continuous noise.…”

“…We measured reproductive success and survival during an experiment (similar as done in Prosnier et al, 2022). We collected gravid D. magna from aquarium and isolated them in 50 mL jars containing Volvic ® water.…”

“…Consequently, we expected that motorboat noise stresses D. magna , and thus negatively affects their fitness, by reducing survival or fecundity or both, according to McCauley et al (2017). However, note that Prosnier et al (2022) surprisingly showed a higher survival of individuals exposed to noise.…”

“…Recent works showed contradictory results concerning their response to noise. It was found no change in their mobility when exposed to acute noise (Sabet et al, 2015, 2019), whereas prior experiment on broadband noise chronic exposure (i.e., a continuous noise) showed that noise was able to alter both fitness and behaviour (Prosnier et al, 2022). Consequently, we expected that motorboat noise stresses D. magna , and thus negatively affects their fitness, by reducing survival or fecundity or both, according to McCauley et al (2017).…”