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.Abstract
Schematic of water flow for hyperbaric system used in CO2 experiments. Complete description of system is provided in the Methods section. Hyperbaric system shown includes nine test chambers connected to a single water and CO2 source.
Larval mortality (expressed as a percentage of individuals exposed for 24 h) as a function of dissolved CO2 concentration. Each point represents the mortality documented using nine tadpoles per CO2 concentration trial. The 24-h LC50 is denoted by a black diamond at 371 mg CO2/L.
A summary of the body condition index for tadpoles used in the 24-h LC50 experiments (N = 135). Tadpoles were lumped into two groups: those that survived (N = 83) or died (N = 52) during 24 h of CO2 exposure, regardless of concentration.
Blood analyte summaries for tadpoles exposed to 450 mg CO2/L for 0, 3, 6, or 9 h: (a) pH, (b) partial pressure of CO2 (pCO2 in mm Hg), and (c) glucose levels (mg/dl) . Different letters indicate statistical differences among treatments at the P < 0.05 level.
Contributor Notes
