Robust quantification of fish early life CO₂ sensitivities via serial experimentation

Despite the remarkable expansion of laboratory studies, robust estimates of single species CO₂ sensitivities remain largely elusive. We conducted a meta-analysis of 20 CO₂ exposure experiments conducted over 6 years on offspring of wild Atlantic silversides (Menidia menidia) to robustly constrain CO₂ effects on early life survival and growth. We conclude that early stages of this species are generally tolerant to CO₂ levels of approximately 2000 µatm, likely because they already experience these conditions on diel to seasonal timescales. Still, high CO₂ conditions measurably reduced fitness in this species by significantly decreasing average embryo survival (-9%) and embryo+larval survival (-13%). Survival traits had much larger coefficients of variation (greater than 30%) than larval length or growth (3-11%). CO₂ sensitivities varied seasonally and were highest at the beginning and end of the species' spawning season (April-July), likely due to the combined effects of transgenerational plasticity and maternal provisioning. Our analyses suggest that serial experimentation is a powerful, yet underused tool for robustly estimating small but true CO₂ effects in fish early life stages.