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.