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

Chair: Gretchen Hofmann

Sara G. Shen (1)*, David M. Checkley, Jr. (1)

1 Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, 92093, USA

Background
We investigated the effects of pCO2 on the (1) morphology and behavior of fish larvae in laboratory experiments and (2) distribution and abundance of fish eggs and larvae in an upwelling system. We hypothesized that elevated pCO2 would increase the size of the utricular otoliths and alter the vestibulo-ocular reflex (VOR). The VOR is a compensatory eye rotation that serves to maintain a stable image during movement, initiated by otolith stimulation. We also hypothesized that eggs and larvae would not be found in areas of high pCO2 in the Peruvian upwelling system.

Methods
To investigate (1), we reared larval white seabass (Atractoscion nobilis) under elevated pCO2 (2500 μatm) and measured the area of the utricular otoliths. The gain and phase of the VOR was quantified from videos of the eye movement of larvae during rotation. To explore (2), we collected eggs and larvae of Peruvian anchoveta (Engraulis ringens) during a fisheries research cruise and data on pCO2 and other environmental variables.

Findings
We identified a 38% increase in the area of the utricular otoliths of larval white seabass reared at 2500 μatm pCO2. The mean gain of treatment larvae (0.39 ± 0.05) was not statistically different from that of control larvae (0.30 ± 0.03). In the Peruvian upwelling system, the probability of egg capture was maximal at the lowest (<350 μatm) and highest (>1000 μatm) pCO2 while larval abundance peaked at low pCO2 (< 600 μatm).

Conclusions
The non-significant effect of pCO2 on the VOR may be a result of its plasticity. Our results suggest that adult anchoveta did not spawn in areas with environmental conditions that were optimal for the survival of their offspring. It may be that the large concentration of eggs spawned at high pCO2 suffered a higher mortality rate than those spawned at lower pCO2.