The effect of temporal variation in sound exposure on swimming and foraging behaviour of captive zebrafish

Anthropogenic noise of variable temporal patterns is increasing in both marine and freshwater systems. Aquatic animals often rely on sounds for communication and orientation, which may therefore become more difficult. Predator-prey interactions may be affected by masking of auditory cues, sound-related disturbance or attentional interference. Here, we investigated the impact on both predator and prey for zebrafish, Danio rerio, preying on water fleas, Daphnia magna. We experimentally raised ambient sound levels in an aquarium and tested four sound conditions that varied in temporal pattern: continuous, fast and slow regular intermittent and irregular intermittent, which we compared with ambient sound levels with no extra exposure. We found no effects on water flea swimming speed or depth but there was an increasing number of individual zebrafish with an increased number of startle responses, especially to the intermittent sound treatments, which was also reflected in a significant increase in zebrafish swimming speed, but not in any change in zebrafish swimming depth. Discrimination in attacking edible water fleas or inedible duckweed particles was low for the zebrafish and unaffected by sound exposure, but foraging was affected in two ways: intermittent sounds delayed the initial acceleration response and all treatments caused a rise in handling error. These insights confirm that elevated sound levels, and especially intermittent conditions, may affect predator-prey interactions. Our results apply to laboratory conditions but call for outdoor studies that go beyond single-species effects. If acoustic impact of human activities extends to multiple species and their interactions, natural sound conditions may turn out to be important for the stability and dynamics of aquatic ecosystems.