Near future pH conditions severely impact calcification, metabolism and the nervous system in the pteropod Heliconoides inflatus

Shelled pteropods play key roles in the global carbon cycle and food webs of various ecosystems. Their thin external shell is sensitive to small changes in pH and shell dissolution has already been observed in areas where aragonite saturation state is ~ 1. A decline in pteropod abundance has the potential to disrupt trophic networks and directly impact commercial fisheries. Therefore it is crucial to understand how pteropods will be affected by global environmental change, particularly ocean acidification. In the present study, physiological and molecular approaches were used to investigate the response of the Mediterranean pteropod, Heliconoides inflatus, to pH values projected for 2100 under a moderate emissions trajectory (RCP6.0). Pteropods were subjected to pHT 7.9 for 3 d, and gene expression levels, calcification and respiration rates were measured relative to pHT 8.1 controls. Gross calcification decreased markedly under low pH conditions, while genes potentially involved in calcification were up-regulated, reflecting the inability of pteropods to maintain calcification rates. Gene expression data imply that under low pH conditions both metabolic processes and protein synthesis may be compromised, while genes involved in acid-base regulation were up-regulated. A large number of genes related to nervous system structure and function were also up-regulated in the low pH treatment, including a GABAA receptor subunit. This observation is particularly interesting because GABAA receptor disturbances, leading to altered behaviour, have been documented in several other marine animals after exposure to elevated CO2. The up-regulation of many genes involved in nervous system function suggests that exposure to low pH could have major effects on pteropod behaviour. This study illustrates the power of combining physiological and molecular approaches. It also reveals the importance of behavioural analyses in studies aimed at understanding the impacts of low pH on marine animals.

Moya A., Howes E. L., Lacoue-Labarthe T., Forêt S., Hanna B., Medina M., Munday P. L., Ong J.-S., Teyssié J.-L., Torda G., Watson S.-A., Miller D. J., Bijma J. & Gattuso J.-P., 2016. Near future pH conditions severely impact calcification, metabolism and the nervous system in the pteropod Heliconoides inflatus. Global Change Biology. Article (subscritpion required).

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