Valve gaping behavior of bivalves under compound marine heatwaves and acidification extremes

Rapid increases in atmospheric carbon dioxide have led to more frequent and severe extreme weather events, such as marine heatwaves (MHWs) and ocean acidity extremes (OAXs), which can devastate marine ecosystems and cause significant socioeconomic impacts. Infaunal bivalves are crucial for benthic-pelagic coupling in marine ecosystems, yet their responses to extreme weather events are poorly understood. In this study, we employed high-frequency, non-invasive valvometry to investigate how Manila clams (Ruditapes philippinarum) behave in response to MHWs and OAXs. Long-term, real-time monitoring showed that initial exposure to MHWs notably reduced valve-gaping activity, though these effects diminished with repeated exposure. OAXs alone significantly impacted the proportion of open valves, but when combined with MHWs, they had a more pronounced effect on individual valve-gaping activity. These results suggest that Manila clam behavior is sensitive to both MHWs and OAXs, particularly when occurring together, highlighting the potential for developing an early-warning system based on valvometry.