A widely distributed epifaunal clam, Chama macerophylla, exhibits compensatory responses to ocean warming and acidification

Global ocean change can negatively impact bivalves, that serve to increase microhabitat and clarify waters in coastal ecosystems. Although effects of global stressors on commercial bivalves have been studied, predicting effects on non-commercial species is challenging due to species-specific responses and potential for synergistic or antagonistic effects when stressors are combined. We assessed the impact of global ocean change on the leafy jewel box clam, Chama macerophylla, a widely distributed epifaunal species. We focused on clams in the northern Gulf of Mexico, where amplified warming and acidification are anticipated. We hypothesized adult clams would experience heightened physiological stress when exposed to warming and acidification, with synergistic effects to combined stressors. Moderate and extreme stressor(s) used in experiments were seldom to never recorded in clam habitat. Yet, 98% of clams survived a 30-day laboratory exposure to single and combined stressor(s). Shells were bimineralic and no alterations in mineral composition were observed. Initially, clams at ambient carbonate chemistry showed increased respiration with higher temperatures, that were subsequently lower by day 30. Notably, clams, when at a constant ambient temperature, exhibited the highest calcification in the most acidic waters, suggesting a compensatory mechanism. When both stressors were present, respiration did not increase as expected with warmer temperatures, and extreme conditions led to variable calcification. Physiological responses from multi-stressor experiments were not statistically relatable to the stress condition, making it challenging to discern impacts of multi-stressors. This study highlights the importance of understanding adaptive mechanisms and long-term stress on bivalves crucial to benthic-pelagic coupling.