Interactive effects of elevated temperature and CO2 levels on energy metabolism and biomineralization of marine bivalves Crassostrea virginica and Mercenaria mercenaria

The continuing increase of carbon dioxide (CO2) levels in the atmosphere leads to increases in global temperatures and partial pressure of CO2 (P-CO2) in surface waters, causing ocean acidification. These changes are especially pronounced in shallow coastal and estuarine waters and are expected to significantly affect marine calcifiers including bivalves that are ecosystem engineers in estuarine and coastal communities. To elucidate potential effects of higher temperatures and P-CO2 on physiology and biomineralization of marine bivalves, we exposed two bivalve species, the eastern oysters Crassostrea virginica and the hard clams Mercenaria mercenaria to different combinations of P-CO2 (similar to 400 and 800 mu atm) and temperatures (22 and 27 degrees C) for 15 weeks. Survival, bioenergetic traits (tissue levels of lipids, glycogen, glucose and high energy phosphates) and biomineralization parameters (mechanical properties of the shells and activity of carbonic anhydrase, CA) were determined in clams and oysters under different temperature and P-CO2 regimes. Our analysis showed major inter-species differences in shell mechanical traits and bioenergetics parameters. Elevated temperature led to the depletion of tissue energy reserves indicating energy deficiency in both species and resulted in higher mortality in oysters. Interestingly, while elevated P-CO2 had a small effect on the physiology and metabolism of both species, it improved survival in oysters. At the same time, a combination of high temperature and elevated P-CO2 lead to a significant decrease in shell hardness in both species, suggesting major changes in their biomineralization processes. Overall, these studies show that global climate change and ocean acidification might have complex interactive effects on physiology, metabolism and biomineralization in coastal and estuarine marine bivalves. (C) 2013 Elsevier Inc. All rights reserved.