Effects of Ocean Acidification on Fish Eggs and Larvae in Laboratory Experiments and Naturally High-pCO2 Upwelling Systems

We investigated the effects of elevated pCO₂ on (1) the morphology and behavior of fish larvae in laboratory experiments and (2) the distribution and abundance of fish eggs and larvae in an upwelling system. The vestibulo-ocular reflex (VOR) is a compensatory eye rotation that stabilizes images during movement and is initiated by utricular otolith movement. It is critically important for survival. We identified a 38% increase in the area of the utricular otoliths of larval white seabass (Atractoscion nobilis) reared at 2500 μatm pCO₂ (treatment) compared to that of larvae reared at 400 μatm pCO₂ (control). Despite the increase in otolith size, the mean gain of treatment larvae (0.39 ± 0.05, n= 28) was not statistically different from that of control larvae (0.30 ± 0.03, n= 20). During a fisheries research cruise in the Peruvian upwelling system in 2013, we collected eggs and larvae of Peruvian anchoveta (Engraulis ringens) over a wide range of pCO₂, from 200-1200 μatm. Anchoveta support the world’s largest single-species fishery and reside in arguably the most persistently high-pCO₂ environment in the ocean. The probability of egg capture was maximal at the lowest (<350 μatm) as well as highest (>1000 μatm) pCO₂ and increased with increasing chlorophyll a concentration. Larval abundance was maximal in the mid-range of zooplankton biovolume (1-3 cm³/1,000 m³). The occurrence of eggs in high pCO₂ and relationship of eggs and larvae to food availability are consistent with the hypothesis that anchoveta tolerate a high pCO₂ and food environment. Our research on the early life stages of these two fish leads us to believe that species that have evolved in high-pCO₂ environments (e.g., anchoveta) may be able to cope with OA. Furthermore, OA may have only subtle effects on behaviors that are critical for survival (e.g., VOR).