The responses of freshwater mussels (<i>Nodularia nipponensis</i>) to vibration.

<p>Many construction works in aquatic environments, such as pile driving, directly induce vibrations into the riverbed. Although benthic animals may be affected by these vibration, their impacts have not been adequately considered during construction works. This study aimed to examine mitigation measures for the rare bivalve species, Nodularia nipponensis, during pile driving activities in their habitat vicinity. Vibrations were measured on the riverbed near the construction site, and laboratory experiments were performed to understand the responses of N. nipponensis under different vibration acceleration levels and frequencies in a controlled environment. Long-term effects of continuous vibration exposure (33 days) were also examined. We found that the vibration threshold for N. nipponensis was within the vibration acceleration level of 80 to 90 dB, with strong reactions observed around frequencies of 40 Hz and 100 Hz. Considering the vibrations generated during pile driving (85 dB and 20-80 Hz at 5 meters from the source), it was inferred that individuals near the vibratory hammer were likely to respond to the vibrations during pile driving. In the long-term experiment with continuous vibration exposure, no significant difference in wet weight change was observed between the vibration-stimulated group and the non-stimulated group. Our results suggest that N. nipponensis responds to intermittent vibrations but not to continuous ones and that frequent intermittent vibration exposure may cause longer shell closure periods, potentially resulting in adverse effects on their growth. Therefore, vibratory-type machinery should be selected to reduce the impact of pile driving on N. nipponensis.</p>