European sea bass, Dicentrarchus labrax, in a changing ocean

Abstract. Ocean acidification, caused by rising concentrations of carbon dioxide (CO₂), is widely considered to be a major global threat to marine ecosystems. To investigate the potential effects of ocean acidification on the early life stages of a commercially important fish species, European sea bass (Dicentrarchus labrax), 12 000 larvae were incubated from hatch through metamorphosis under a matrix of two temperatures (17 and 19 °C) and two seawater pCO₂ levels (ambient and 1,000 μatm) and sampled regularly for 42 days. Calculated daily mortality was significantly affected by both temperature and pCO₂, with both increased temperature and elevated pCO₂ associated with lower daily mortality and a significant interaction between these two factors. There was no significant pCO₂ effect noted on larval morphology during this period but larvae raised at 19 °C possessed significantly larger eyes and lower carbon:nitrogen ratios at the end of the study compared to those raised under 17 °C. Similarly, when the incubation was continued to post-metamorphic (juvenile) animals (day 67–69), fish raised under a combination of 19 °C and 1000 μatm pCO₂ were significantly heavier. However, juvenile D. labrax raised under this combination of 19 °C and 1000 μatm pCO₂ also exhibited lower aerobic scopes than those incubated at 19 °C and ambient pCO₂. Most studies investigating the effects of near-future oceanic conditions on the early life stages of marine fish have used incubations of relatively short durations and suggested that these animals are resilient to ocean acidification. Whilst the increased survival and growth observed in this study supports this view, we conclude that more work is required to investigate whether the differences in juvenile physiology observed in this study manifest as negative impacts in adult fish.