Diel-cycling seawater acidification and hypoxia impair the physiological and growth performance of marine mussels

Highlights

• The combined effects of acidification and hypoxia on physiological performance of mussels were investigated.

• Diel fluctuating hypoxia and acidification had less impact on the internal environment of mussels compared with constant exposure.

• Mussels had higher growth performance under diel cycling acidification and hypoxia compared with constant exposure.

• Mussels showed stronger resistance to diel cycling seawater acidification and hypoxia than constant exposure.

Abstract

Ocean acidification and hypoxia are concurrent in some coastal waters due to anthropogenic activities in the past decades. In the natural environment, pH and dissolved oxygen (DO) may fluctuate and follow diel-cycling patterns, but such effects on marine animals have not been comprehensively studied compared to their constant effects. In order to study the effects of diel-cycling seawater acidification and hypoxia on the fitness of marine bivalves, the thick shell mussels Mytilus coruscus were exposed to two constant levels of dissolved oxygen (2 mg/L, 8 mg/L) under two pH treatments (7.3, 8.1), as well as single diel fluctuating pH or DO, and the combined diel fluctuating of pH and DO for three weeks. The experimental results showed that constant acidification and hypoxia significantly reduced the extracellular pH (pHe) and condition index (CI) of mussels, and significantly increased HCO3−, pCO2 and standard metabolic rate (SMR). Diel fluctuating hypoxia and acidification also significantly reduced the pHe and CI, and significantly increased pCO2 and SMR, but had no significant effects on HCO3−. However, the diel-cycling acidification and hypoxia resulted in a higher CI compared to continuous exposure. In general, continuous and intermittent stress negatively impact the hemolymph and growth performance of mussels. However, mussels possess a little stronger resistance to diel-cycling seawater acidification and hypoxia than sustained stress.

Shang Y., Wang X., Deng Y., Wang S., Gu H., Wang T., Xu G., Kong H., Feng Y., Hu M. & Wang Y., 2020. Diel-cycling seawater acidification and hypoxia impair the physiological and growth performance of marine mussels. Science of The Total Environment 722: 138001. doi: 10.1016/j.scitotenv.2020.138001. Article (subscription required).

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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book