Physiological responses of three species of unionid mussels to intermittent exposure to elevated carbon dioxide

Zones of elevated carbon dioxide (CO 2 ) have been proposed as barriers to fish movements, but impacts of CO 2 on non-target sensitive organisms are unknown. In the present study, freshwater mussels were exposed to intermittent elevations in CO 2 and showed species-specific mechanisms to regulate acid–base disturbances, along with a stress response.