Impact of salinity changes on burrowing behavior and energy metabolism in juvenile razor clam (Sinonovacula constricta)

The razor clam Sinonovacula constricta is a commercially valuable bivalve in East Asia in intertidal and estuarine soft-bottom habitats; however, wild stocks have declined dramatically in some regions such as Ariake Bay in Japan and this has prompted local governments to implement seedling production and release programs. To assess the effects of salinity fluctuations on juvenile clams after release, two salinity change scenarios, gradual increase (from 25 to 30) and rapid decrease (from 27 to 7), were simulated in the laboratory to examine temporal changes in osmotic regulation, burrowing behavior, and energy metabolism. Gradual salinity increases did not significantly affect the measured parameters (P > 0.05). However, rapid salinity decreases significantly reduced levels of the osmotic regulator alanine (P < 0.01), indicating activation of osmotic adjustment. Additionally, most individuals under rapidly decreasing salinity conditions ceased mud burrowing (P < 0.01), exhibited glycogen depletion (P < 0.001), showed decreased aspartic acid levels (P < 0.001), and accumulated propionic acid (P < 0.001). In summary, rapid salinity decreases elevate energy demands for osmotic regulation in S. constricta, thereby suppressing burrowing activity and triggering anaerobic metabolism due to glycogen depletion. Notably, even under aerobic conditions, juvenile razor clams compensate for glycogen depletion by activating anaerobic pathways to sustain energy production. These findings provide insights into the physiological and behavioral responses of S. constricta to salinity stress, with implications for their management and conservation in variable estuarine environments.