Upper environmental pCO2 drives sensitivity to ocean acidification in marine invertebrates

Minimizing the impact of ocean acidification requires an understanding of species responses and environmental variability of population habitats. Whereas the literature is growing rapidly, emerging results suggest unresolved species- or population-specific responses. Here we present a meta-analysis synthesizing experimental studies examining the effects of pCO2 on biological traits in marine invertebrates. At the sampling locations of experimental animals, we determined environmental pCO2 conditions by integrating data from global databases and pCO2 measurements from buoys. Experimental pCO2 scenarios were compared with upper pCO2 using an index considering the upper environmental pCO2. For most taxa, a statistically significant negative linear relationship was observed between this index and mean biological responses, indicating that the impact of a given experimental pCO2 scenario depends on the deviation from the upper pCO2 level experienced by local populations. Our results highlight the importance of local biological adaptation and the need to consider present pCO2 natural variability while interpreting experimental results.