Description: Productivity of marine fish stocks is known to be affected by environmental and ecological drivers, and global climate change is anticipated to alter recruitment success of many stocks. While the direct effects of environmental drivers on fish early life stage survival can be quantified experimentally, indirect effects in marine ecosystems and the role of adaptation are still highly uncertain. We developed an integrative model for the effects of ocean warming and acidification on the early life stages of Atlantic cod in the Barents Sea, termed SCREI (Simulator of Cod Recruitment under Environmental Influences). Experimental results on temperature and CO2 effects on egg fertilization, egg and larval survival and development times are incorporated. Calibration using empirical time series of egg production, temperature, food and predator abundance reproduces age-0 recruitment over three decades. We project trajectories of recruitment success under different scenarios and quantify confidence limits based on variation in experiments. A publicly accessible web version of the SCREI model can be run under www.oceanchange.uni-bremen.de/;SCREI. Severe reductions in average age-0 recruitment success of Barents Sea cod are projected under uncompensated warming and acidification toward the middle to end of this century. Although high population stochasticity was found, considerable rates of evolutionary adaptation to acidification and shifts in organismal thermal windows would be needed to buffer impacts on recruitment. While increases in food availability may mitigate short-term impacts, an increase in egg production achieved by stock management could provide more long-term safety for cod recruitment success. The SCREI model provides a novel integration of multiple driver effects in different life stages and enables an estimation of uncertainty associated with interindividual and ecological variation. The model thus helps to advance toward an improved empirical foundation for quantifying climate change impacts on marine fish recruitment, relevant for ecosystem-based assessments of marine systems under climate change.

Description: In order to understand the effect of global change on marine fishes, it is imperative to quantify the effects on fundamental parameters such as survival and growth. Larval survival and recruitment of the Atlantic cod (Gadus morhua) were found to be heavily impaired by end-of-century levels of ocean acidification. Here, we analysed larval growth among 35–36 days old surviving larvae, along with organ development and ossification of the skeleton. We combined CO2treatments (ambient: 503 µatm, elevated: 1,179 µatm) with food availability in order to evaluate the effect of energy limitation in addition to the ocean acidification stressor. As expected, larval size (as a proxy for growth) and skeletogenesis were positively affected by high food availability. We found significant interactions between acidification and food availability. Larvae fed ad libitum showed little difference in growth and skeletogenesis due to the CO2 treatment. Larvae under energy limitation were significantly larger and had further developed skeletal structures in the elevated CO2 treatment compared to the ambient CO2 treatment. However, the elevated CO2 group revealed impairments in critically important organs, such as the liver, and had comparatively smaller functional gills indicating a mismatch between size and function. It is therefore likely that individual larvae that had survived acidification treatments will suffer from impairments later during ontogeny. Our study highlights important allocation trade-off between growth and organ development, which is critically important to interpret acidification effects on early life stages of fish.