Selective preferences and behavioral adaptation strategy of Pacific abalone in response to different water flow velocities

The water flow velocity is a crucial environmental physical factor that drastically impacts the survival and stock distribution of marine organisms. To facilitate the restoration of wild stocks of Pacific abalone (Haliotis discus hannai) and increase the success rate of release, abalones were monitored for 24 h without interruption in an experimental unit (developed in-house) to assess the flow velocity preferences of marine mollusks. Abalones tended to keep away from areas with higher flow velocities (> 5 cm/s) and they preferred to stay in areas with lower flow velocities (< 5 cm/s). Comparative study of the diurnal behavioral characteristics of abalones under seven different flow velocities (0, 5, 10, 15, 20, 25, and 30 cm/s) showed that the cumulative distance moved, movement duration, and feeding time decreased significantly as the flow velocity increased. At flow velocities over 20 cm/s, abalones barely moved or consumed food, and cosine rhythm analysis demonstrated that the diurnal rhythms of behavioral parameters disappeared and the peak movement phase occurred earlier than expected. In addition, increasing the flow velocity reduced the spacing between individuals and the polarity of movement was higher. Individuals changed their coordination levels in groups as an active adaptation to changes in the flow velocity. These findings provide new insights into the ecological habits of abalones. Based on the characteristic movement behaviors of abalones at different flow velocities, bottom-sowing should be conducted in areas with a flow velocity < 5 cm/s instead of areas with a flow velocity > 20 cm/s to improve the efficiency of bottom-sowing stock enhancement.