The physiological and behavioral effects of ocean acidification (OA) on the early life stages of marine fish are largely unknown. Because any negative effects of OA on eggs and larvae can greatly impact fisheries productivity and ecosystem function, gaining a mechanistic understanding of OA effects is a key research priority. The primary goal of this study is to determine potential direct effects of OA on a key species in the California Current Ecosystem, the northern anchovy. The scientists will collect northern anchovy eggs from San Diego and Cape Mendocino – two areas with varied seawater pCO2 and spawning seasons. The eggs will be exposed to varied treatments of pCO2 concentration prior to analysis of gene expression and larval behavior. A mechanistic understanding of OA response may provide a general understanding of how fish larvae acclimate to this stress. Comparisons between two populations that naturally experience different levels of OA may provide evidence for rapid evolutionary adaptation to environmental change.