ALBERT

Description: Survival of marine fishes exposed to elevated near-future CO2 levels is threatened by their altered responses to sensory cues. Here we demonstrate a novel physiological and molecular mechanism based in the olfactory system which helps explain altered behavior under elevated CO2. We combine electrophysiology and high throughput sequencing with behavioral experiments to investigate how elevated CO2 affects the olfactory system of European sea bass (Dicentrarchus labrax), an economically important species. Under elevated CO2 (~1000 µatm) fish need to be up to 42% closer to an odor source for detection, compared with current CO2 levels (~400 µatm), decreasing their chances of detecting food or predators. These findings correlated with a suppression in the transcription of genes involved in synaptic strength, cell excitability, and wiring of the olfactory system in response to sustained exposure to elevated CO2. Our results contrast with, but complement, the previously proposed mechanism of impaired neurotransmitter (?-aminobutyric acid) function, and demonstrate that both the olfactory system and central brain function are compromised by elevated CO2 in the oceans, with potentially major negative impacts on fish globally.

Description: 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.