Impacts of marine heatwaves on bivalves during reproduction

Marine heatwaves (MHWs) have increased in frequency, intensity, and duration in this era of unprecedented climate change, posing significant threats to bivalves. Yet, the consequences of MHWs for bivalves during reproductive conditioning, which are vital for the recruitment success and population maintenance, remain largely unknown. Here, we assessed the impact of intensifying MHWs on economically and ecologically significant clams (Ruditapes philippinarum) during gonadal maturation. The survival of clams significantly decreased to 56 % following repeated exposure to the most severe thermal scenario of MHWs (22 °C-32 °C for 5 days and then recovery at 22 °C for 5 days for each event). Qualitative evidence suggests that intensifying MHWs resulted in irreversible gonadal impairments in both female and male clams even after two recovery periods. With increasing frequency and intensify of MHWs, activities of energy-metabolizing enzymes (NKA, CMA, and T-ATP) decreased initially and then increased significantly. This pattern agreed well with changes in enzyme performances (e.g., SOD, CAT, MDA, AKP, ACP) and associated gene expressions in the gill antioxidant and immune defence system. Our, our findings demonstrate that R. philippinarum exhibits physiological plasticity in response to MHWs. However, significant increases in mortality and irreversible impairments in gonads underscore the profound impact of intensifying MHWs on bivalves during reproduction, which can affect recruitment success and population maintenance.