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

Development of Carbon Dioxide Barriers to Deter Invasive Fishes: Insights and Lessons Learned from Bigheaded Carp

Invasive species are a threat to biodiversity in freshwater. Removing an aquatic invasive species following arrival is almost impossible, and preventing introduction is a more viable management option. Bigheaded carp are an invasive fish spreading throughout the Midwestern United States and are threatening to enter the Great Lakes. This review outlines the development of carbon dioxide gas (CO2) as a non-physical barrier that can be used to deter the movement of fish and prevent further spread. Carbon dioxide gas could be used as a deterrent either to cause avoidance (i.e., fish swim away from zones of high CO2), or by inducing equilibrium loss due to the anesthetic properties of CO2 (i.e., tolerance). The development of CO2 as a fish deterrent started with controlled laboratory experiments demonstrating stress and avoidance, and then progressed to larger field applications demonstrating avoidance at scales that approach real-world scenarios. In addition, factors that influence the effectiveness of CO2 as a fish barrier are discussed, outlining conditions that could make CO2 less effective in the field; these factors that influence efficacy would be of interest to managers using CO2 to target other fish species, or those using other non-physical barriers for fish.

Hot and bothered: effects of elevated Pco2 and temperature on juvenile freshwater mussels

Multiple environmental stressors may interact in complex ways to exceed or diminish the impacts of individual stressors. In the present study, the interactive effects of two ecologically relevant stressors [increased temperature and partial pressure of carbon dioxide (Pco2)] were assessed for freshwater mussels, a group of organisms that are among the most sensitive and rapidly declining worldwide. The individual and combined effects of elevated temperature (22°C–34°C) and Pco2 (~230, 58,000 µatm) on juvenile Lampsilis siliquoidea were quantified over a 5- or 14-day period, during which physiological and whole animal responses were measured. Exposure to elevated temperature induced a series of physiological responses, including an increase in oxygen consumption rates following 5 days of exposure at 31°C and an increase in carbonic anhydrase ( ca) and heat shock protein 70 mRNA levels following 14 days of exposure at 28°C and 34°C, respectively. Treatment with elevated Pco2 activated acid-base regulatory responses including increases in CA and Na+-K+-ATPase activity and a novel mechanism for acid-base regulation during Pco2 exposure in freshwater mussels was proposed. Thermal and CO2 stressors also interacted such that responses to the thermal stressor were diminished in mussels exposed to elevated Pco2, resulting in the greatest level of mortality. Additionally, larger mussels were more likely to survive treatment with elevated Pco2 and/or temperature. Together, exposure to elevated Pco2 may compromise the ability of juvenile freshwater mussels to respond to additional stressors, such as increased temperatures, highlighting the importance of considering not only the individual but also the interactive effects of multiple environmental stressors.

Chronic exposure of a freshwater mussel to elevated pCO2 : Effects on the control of biomineralization and ion-regulatory responses

Freshwater mussels may be exposed to elevations in mean partial pressure of carbon dioxide (pCO₂ ) caused by both natural and anthropogenic factors. The goal of the present study was to assess the effects of a 28-d elevation in pCO₂ at 15 000 and 50 000 μatm on processes associated with biomineralization, ion regulation, and cellular stress in adult Lampsilis siliquoidea (Barnes, 1823). In addition, the capacity for mussels to compensate for acid-base disturbances experienced after exposure to elevated pCO₂ was assessed over a 14-d recovery period. Overall, exposure to 50 000 μatm pCO₂ had more pronounced physiological consequences compared with 15 000 μatm pCO₂ . Over the first 7 d of exposure to 50 000 μatm pCO₂ , the mRNA abundance of chitin synthase (cs), calmodulin (cam), and calmodulin-like protein (calp) were significantly affected, suggesting that shell formation and integrity may be altered during pCO₂ exposure. After the removal of the pCO₂ treatment, mussels may compensate for the acid-base and ion disturbances experienced during pCO₂ exposure, and transcript levels of some regulators of biomineralization (carbonic anhydrase [ca], cs, cam, calp) as well as ion regulation (na⁺ -k⁺ -ATPase [nka]) were modulated. Effects of elevated pCO₂ on heat shock protein 70 (hsp70) were limited in the present study. Overall, adult L. siliquoidea appeared to regulate factors associated with the control of biomineralization and ion regulation during and/or after the removal of pCO₂ exposure. Environ Toxicol Chem 2018;37:538-550. © 2017 SETAC.

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.