Is the perceived resiliency of fish larvae to ocean acidification masking more subtle effects?

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 (<i>Dicentrarchus labrax</i>), 12 000 larvae were incubated from hatch through metamorphosis under a matrix of two temperatures (17 and 19 °C) and two seawater <i>p</i>CO₂s (400 and 750 μatm) and sampled regularly for 42 days. Calculated daily mortality was significantly affected by both temperature and <i>p</i>CO₂, with both increased temperature and elevated <i>p</i>CO₂ associated with lower daily mortality and a significant interaction between these two factors. There was no significant <i>p</i>CO₂ 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. These results suggest that <i>D. labrax</i> larvae are resilient to near-future oceanic conditions. However, when the incubation was continued to post-metamorphic (juvenile) animals (day 67–69), fish raised under a combination of 19 °C and 750 μatm <i>p</i>CO₂ were significantly heavier and exhibited lower aerobic scopes than those incubated at 19 °C and 400 μatm. Most other 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 these animals are resilient to ocean acidification. We propose the durations of these other studies may be insufficient for more subtle effects, such as those observed in this study, to become apparent. These findings may have important implications for both sea bass in a changing ocean and also for the interpretation of results from other studies that have shown resiliency in marine teleosts exposed to higher atmospheric concentrations of CO₂

Growth performance and survival of larval Atlantic herring, under the combined effects of elevated temperatures and CO2

“…The performance of fish species and their developmental stages should be best around their abiotic and biotic optimum [ 9 ]. The theoretical optimal temperature of a species corresponds to optimal [ 10 ] or even suboptimal [ 11 ] growth temperatures and may interact with future CO 2 concentrations, as observed for larval European sea bass ( Dicentrarchus labrax ) [ 12 ] and Senegalese sole ( Solea senegalensis ) [ 13 ]. Larval European sea bass displayed higher survival at increased temperatures and elevated p CO 2 levels, leading to heavier juveniles in the warm treatment and lower aerobic scope under elevated p CO 2 levels [ 12 ].…”

“…The theoretical optimal temperature of a species corresponds to optimal [ 10 ] or even suboptimal [ 11 ] growth temperatures and may interact with future CO 2 concentrations, as observed for larval European sea bass ( Dicentrarchus labrax ) [ 12 ] and Senegalese sole ( Solea senegalensis ) [ 13 ]. Larval European sea bass displayed higher survival at increased temperatures and elevated p CO 2 levels, leading to heavier juveniles in the warm treatment and lower aerobic scope under elevated p CO 2 levels [ 12 ]. In contrast, the early life stages of Senegalese sole showed strong negative impacts of increased p CO 2 and temperatures on hatching success and survival, while larval growth and metabolism were positively affected by increased temperature but negatively affected by increased p CO 2 [ 13 ].…”