Behavioural Responses to Ultrasound Antifouling Systems by Adult Solitary Ascidians

Ultrasonic antifouling devices are installed globally on a variety of vessel types and are marketed as an environmentally friendly method for biofouling control. The aim of this study was to examine the effects of ultrasound on adults of three species of common solitary ascidians (Ciona intestinalis, Ascidiella aspersa and Styela plicata). After a brief (10 s) exposure to two ultrasound frequencies (30 and 35 kHz), alterations in the frequency of siphon closing events and the length of time the siphons remained closed/open were observed. The results revealed that ascidians are able to perceive ultrasound, showing frequency-dependent behavioural responses that vary depending on the species and size of individuals involving both tactile receptors and an acoustic system homologous to the vertebrate inner ear. Continuous (5 h) 30 kHz exposure caused other types of responses, the most interesting of which was the long-term opening of the oral siphon, indicating a lack of reactivity to mechanical stimuli. This effect suggests a stress condition that could lead to increased vulnerability to predators and filter-feeding impairment. Therefore, knowledge of the acoustic sensitivity of sessile marine species appears to be essential for better understanding the potential effects of noise pollution on marine ecosystems.