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 (CO2 ) because of the potential use of CO2 to control the movement of invasive aquatic fish species. One potential behavioral response to a change in the partial pressure of CO2 (pCO2 ) may be altered valve movement. In this study, three species of mussels were fitted with modified sensors and exposed to two regimes of pCO2 to define thresholds of impaired valve movement. The first experiment demonstrated that Pyganodon grandis were much more tolerant to rising pCO2 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 pCO2 (∼70,000 μatm) over a 2-day period. During exposure to high pCO2 , Lampsilis cardium were open for nearly the entire high pCO2 period. Conversely, P. grandis were closed for most of the period following exposure to high pCO2 . For L. siliquoidea, the number of closures decreased nearly 40-fold during high pCO2 . The valve movement responses observed suggest species differences, and exposure to elevated pCO2 requires a reactive response.