Toxic dinoflagellate <i>Prorocentrum cordatum</i> affects the filtration rate and enzymatic activities of Chinese razor clam (<i>Sinonovacula constricta</i>)

Harmful algal blooms represent a significant environmental challenge in various marine ecosystems worldwide. While marine filter-feeder bivalves can consume toxic phytoplankton, their capacity to mitigate the presence of harmful microalgae is not yet fully understood. In this study, we examined the filtration rates and enzymatic activities of <i>Sinonovacula constricta</i>, a commercially valuable bivalve, when exposed to varying levels of toxic dinoflagellates (<i>Prorocentrum cordatum</i>) and non-toxic diatoms (<i>Skeletonema costatum</i>) over a 12-h period. Chlorophyll <i>a</i> concentration was used to reflect the presence of these microalgae. In the initial 2 h, the filtration rate under toxic conditions was lower than under non-toxic conditions. However, after the first 2 h, the filtration rate under toxic conditions did not decline as rapidly as it did under non-toxic conditions, suggesting that <i>S. constricta</i> could adapt to the presence of toxic microalgae over time. Regarding enzymatic activities, digestive enzymes were not significantly affected by low concentrations of toxic microalgae, but lipase activity was inhibited at higher concentrations. Antioxidant enzyme activity showed no significant changes across all non-toxic microalgal concentrations. Superoxide dismutase (SOD) activity increased at higher toxic microalgal concentrations, but both low SOD and catalase activities indicated that the bivalve's antioxidant defenses for detoxification may be limited. These results suggest that <i>S. constricta</i> can tolerate toxic microalgae through adaptive feeding behaviors and changes in digestive and antioxidant enzymatic activities. This study revealed <i>S. constricta</i> has a high filtration rate and is sensitive to high concentrations of toxic microalgae. Therefore, its bioremediation function requires further study.