Background and Objectives: Many animal species are currently experiencing anthropogenic pollutions in their habitat. Noise pollution from human activities affects many species of animals. Noise pollution in terrestrial and aquatic ecosystems is prominently recognized as a source of stress and disruption of biological activities, and an important and pervasive global environmental pollutant. Recent studies have shown the effect of sound on various aquatic vertebrates, including fish and marine mammals. However, despite the diversity of invertebrates and crustacean that they are among the earliest links in the food chain in ecosystems, studies on the effect of acoustic stimuli on their behaviour are limited. Therefore, the aim of the present study was to investigate the effect of continuous sound exposure, the most common temporal patten among underwater sound sources, on the behaviour of an invertebrate, red cherry shrimp (Neocaridina davidi) under laboratory conditions.
Methods: In total, 70 red cherry shrimps were housed in a holding aquarium (48 cm × 32 cm × 28 cm; water depth: 22cm; wall thickness: 4mm) connected to a water circulation system on a 14 h light; 10 h dark cycle and with the water temperature kept at 27℃. All shrimp individuals were fed twice daily for two weeks with spirolina tablet before being transferred individually to the experimental set-up. The experiments were conducted in a rectangular glass tank aquarium (40 × 30 × 30 cm; water depth: 20 cm; wall thickness: 2cm) equipped with a custom build underwater speaker connected to a power amplifier. Behavioural experiments were performed after the shrimps had acclimated to the experimental set-up. The shrimps were divided in two treatments and individually exposed either to ambient noise as a control (96.52±1 dB ref 1µPa) or continuous sound (110.40±1 dB ref 1µPa) in a bandwidth range of 400 to 2000 Hz. Here, in this study, we investigated the effect of sound exposure on movement speed, spatial distribution and food finding behaviour of shrimps.
Findings: According to the findings, in general, once the passing gate opened, the movement speed in sound and control treatments showed a significant decrease(P<0.05), but there were no significant changes between total minutes of control and sound treatments(P>0.05). The spatial distribution of shrimps in response to the sound treatment showed significant changes (P<0.05). Moreover, the time to find the food source also increased significantly in the sound treatment (P<0.05).
Conclusion: The findings of this study confirm the effect of sound on the behaviour of red cherry shrimp, under laboratory conditions. Elevated sound levels caused changes in spatial distribution and to some extent movement speed of shrimps. Moreover, sound exposure negatively affected allocated time budget to find food source; shrimps spent more time to find food source. Our study highlights that invertebrate are likely to be susceptible to the impacts of anthropogenic sound. We suggest that sound has the potential to increase the risks of starvation and may have subsequently negative effects on the timing of foraging and predatory- prey activities and that may affect population of meiofauna and benthic organisms in aquatic ecosystems. Finally, our laboratory study should not be extrapolated directly to outdoor conditions, but calls for investigation of behavioural responses of invertebrates to acoustic stimuli.