Ocean acidification exacerbates the impacts of global warming on embryonic little skate, Leucoraja erinacea (Mitchill)

• Development and active metabolic rates exhibit countergradient variation in embryos.
• Thermal optimum for metabolic performance in embryos of both populations is 18 °C.
• Increased warming and acidification reduce body condition of newly-hatched skates.
• Body condition correlates with the latency of hatchlings to begin feeding.
• Acidification has a stronger negative effect on the Gulf of Maine population.

Ocean acidification and warming have the potential to profoundly impact marine fishes by reducing embryo fitness and survival. Local adaptation to thermal gradients may reduce the impact of global warming, but whether fish from different populations may respond differently to climatic stressors remains unknown. The hypothesis that acidification and warming may have an effect on development, aerobic scope, and survival was tested in little skate (Leucoraja erinacea) embryos from two latitudinally separated populations. Temperature had the strongest effect on development, survival and metabolic rates, but acidification further exacerbated stress on embryos from the Gulf of Maine population by increasing the costs of activity, development time, and reducing body condition of newly hatched skates. Active metabolic rates of both populations exhibited countergradient variation with peak of performance at 18 °C, but were affected differently by acidification. These findings demonstrate that even adjacent fish populations may respond differently to increasing temperature and acidification and emphasize the need for multi-stressor studies on different populations of fishes with wide geographic range to understand complex responses to climate change and other environmental challenges.