Suppressing bullfrog larvae with carbon dioxide

Current management strategies for the control and suppression of the American Bullfrog (Lithobates catesbeianus = Rana catesbeiana Shaw) and other invasive amphibians have had minimal effect on their abundance and distribution. This study evaluates the effects of carbon dioxide (CO₂) on pre- and prometamorphic Bullfrog larvae. Bullfrogs are a model organism for evaluating potential suppression agents because they are a successful invader worldwide. From experimental trials we estimated that the 24-h 50% and 99% lethal concentration (LC₅₀ and LC₉₉) values for Bullfrog larvae were 371 and 549 mg CO₂/L, respectively. Overall, larvae that succumbed to experimental conditions had a lower body condition index than those that survived. We also documented sublethal changes in blood chemistry during prolonged exposure to elevated CO₂. Specifically, blood pH decreased by more than 0.5 pH units after 9 h of exposure and both blood partial pressure of CO₂ (pCO₂) and blood glucose increased. These findings suggest that CO₂ treatments can be lethal to Bullfrog larvae under controlled laboratory conditions. We believe this work represents the necessary foundation for further consideration of CO₂ as a potential suppression agent for one of the most harmful invaders to freshwater ecosystems.