Expanding evaluation of ocean acidification responses in a marine gadid: elevated CO2 impacts development, but not size of larval walleye pollock

Responses of marine populations to climate conditions reflect the integration of a suite of complex and interrelated physiological and behavioral responses at the individual level. Many of these responses are not immediately reflected in changes to survival, but may impact growth or survival at later life stages. Understanding the broad range of impacts of rising CO2 concentrations on marine fishes is critical to predicting the consequences of ongoing ocean acidification. Walleye pollock (Gadus chalcogrammus) support the largest single-species fishery in the world and provide a critical forage base throughout north Pacific ecosystems. Previous studies of high CO2 effects on early life stages of walleye pollock have suggested a general resiliency in this species, but those studies focused primarily on growth and survival rates. Here, we expand on earlier studies with an independent experiment focused on walleye pollock larval development, swimming behavior, and lipid composition from fertilization to 4 weeks post-hatch at ambient (~ 425 µatm) and elevated (~ 1230 µatm) CO2 levels. Consistent with previous observations, size metrics of walleye pollock were generally insensitive to CO2 treatment. However, 4-week post-hatch larvae had significantly reduced rates of swim bladder inflation. A modest change in the swimming behavior of post-feeding larvae was observed at four, but not at 2 weeks post-hatch. Although there were no differences in overall lipid levels between CO2 treatments, the ratio of energy storage lipids (triacylglycerols) to structural membrane lipids (sterols) was lower among larvae reared at high CO2 levels. Although we observed higher survival to 4 weeks post-hatch among fish reared at high CO2 levels, the observations of reduced swim bladder inflation rates and changes in lipid cycling suggest the presence of sub-lethal effects of acidification that may carry over and manifest in later life stages. These observations support the continued need to evaluate the impacts of ocean acidification on marine fishes across a wide range of traits and life stages with replicated, independent experiments.