Valve movement of three species of North American freshwater mussels exposed to elevated carbon dioxide

Freshwater mussels are at-risk taxa and may be exposed to high levels of carbon dioxide (CO 2 ) because of the potential use of CO 2 to control the movement of invasive aquatic fish species. One potential behavioral response to a change in the partial pressure of CO 2 (pCO 2 ) may be altered valve movement. In this study, three species of mussels were fitted with modified sensors and exposed to two regimes of pCO 2 to define thresholds of impaired valve movement. The first experiment demonstrated that Pyganodon grandis were much more tolerant to rising pCO 2 relative to Lampsilis siliquoidea (acute closure at ∼200,000 μatm in comparison to ∼80,000 μatm) . The second experiment consisted of monitoring mussels for 6 days and exposing them to elevated pCO 2 (∼70,000 μatm) over a 2-day period. During exposure to high pCO 2 , Lampsilis cardium were open for nearly the entire high pCO 2 period. Conversely, P. grandis were closed for most of the period following exposure to high pCO 2 . For L. siliquoidea , the number of closures decreased nearly 40-fold during high pCO 2 . The valve movement responses observed suggest species differences, and exposure to elevated pCO 2 requires a reactive response.