Predation of Freshwater Fish in Elevated Carbon Dioxide Environments

Increasing CO₂ in freshwater environments is poorly understood, yet often high and variable. Work from marine systems has shown that elevated CO₂ can impact a range of behaviors, including predator–prey relationships. To examine changes in predator success in elevated CO₂, we experimented with predatory largemouth bass (Micropterus salmoides) and fathead minnow (Pimephales promelas) prey. We used a two factor fully crossed experimental design with one factor being a 4-day (acclimation) CO₂ level and the second factor being CO₂ level during 20 minute predation experiments. Both factors had three treatment levels—ambient pCO₂ (0–1,000 matm), low pCO₂ (4,000–5,000 matm), and high pCO₂ (8,000–10,000 matm). Largemouth bass were exposed to both factors while fathead minnows were not exposed to the acclimation factor. 83 of the 96 fathead minnows were consumed during the 96 trials and we saw no discernable impact of CO₂ on predator success or time to predation. Failed strikes and time between failed strikes were too infrequent to model, further supporting very high predation success across all treatments. Compared to studies of fish species in marine systems, our findings are unique in that we not only saw no changes in prey capture success with increasing CO₂, but we also used CO₂ treatments that were substantially higher than in past experiments.