New Methods For Studying Underwater Noise Effects On Microscopic Sessile Marine Invertebrates: Challenges And Perspectives

The negative effects of underwater noise have been studied in a few marine invertebrate species.Scanty information is available on ascidians, filter-feeding tunicates, although they are dominant among epibenthic fauna.In past playback experiments in tanks, the closure rate of the oral siphon of solitary ascidians (about 10 cm long) was evaluated using videos.In a new study, we aimed at verifying the underwater noise effects on Botryllus schlosseri, an ascidian forming colonies of tiny, transparent animals about 1.5 mm long.Since videos were not useful due to the animal's small size, we adjusted and fine-tuned behavioral and physiological tests never used before for analyzing noise effects.We exposed colonies collected in the Venetian Lagoon to continuous noise (30 min; peak bands 63-125 Hz) mimicking the low frequency maritime traffic noise.We adjusted tests evaluating the responsiveness of two different mechanoreceptors of the oral siphon and the heartbeat frequency under the stereomicroscope, and developed an assay for studying the animal filtration rate.Preliminary results show that noise effects can be carefully measured and statistically analyzed.These methods represent new, valuable tools that could be translated in future to other filter-feeding, small and transparent animals or adjusted to large animals.