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 six 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 ~ 2,000 µatm, likely because they already experience these conditions on diel to seasonal time scales. 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 (>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 underutilized tool for robustly estimating small but true CO2 effects in fish early life stages.