Physiological response and resilience of early life-stage Eastern oysters (Crassostrea virginica) to past, present and future ocean acidification.

C J Gobler,S C Talmage

doi:10.1093/conphys/cou004

Abstract

The Eastern oyster, Crassostrea virginica (Gmelin, 1791), is the second most valuable bivalve fishery in the USA and is sensitive to high levels of partial pressure of CO2 (pCO2). Here we present experiments that comprehensively examined how the ocean's past, present and projected (21st and 22nd centuries) CO2 concentrations impact the growth and physiology of larval stages of C. virginica. Crassostrea virginica larvae grown in present-day pCO2 concentrations (380 μatm) displayed higher growth and survival than individuals grown at both lower (250 μatm) and higher pCO2 levels (750 and 1500 μatm). Crassostrea virginica larvae manifested calcification rates, sizes, shell thicknesses, metamorphosis, RNA:DNA ratios and lipid contents that paralleled trends in survival, with maximal values for larvae grown at 380 μatm pCO2 and reduced performance in higher and lower pCO2 levels. While some physiological differences among oysters could be attributed to CO2-induced changes in size or calcification rates, the RNA:DNA ratios at ambient pCO2 levels were elevated, independent of these factors. Likewise, the lipid contents of individuals exposed to high pCO2 levels were depressed even when differences in calcification rates were considered. These findings reveal the cascading, interdependent impact that high CO2 can have on oyster physiology. Crassostrea virginica larvae are significantly more resistant to elevated pCO2 than other North Atlantic bivalves, such as Mercenaria mercenaria and Argopecten irradians, a finding that may be related to the biogeography and/or evolutionary history of these species and may have important implications for future bivalve restoration and aquaculture efforts.

Highlights

Rising levels of atmospheric CO2 have led to world’s oceans acidifying since the dawn of the industrial revolution, a process expected to continue for at least two centuries (Caldeira and Wickett, 2003)
Shell lengths of C. virginica larvae at day 21 were significantly larger (392 ± 9.8 μm) when grown in present-day CO2 conditions (380 μatm), compared with 250 μatm pressure of CO2 (pCO2) (317 ± 4.7 μm), 750 μatm CO2 (208 ± 7.5 μm) or 1500 μatm pCO2 (127 ± 4.6 μm; P < 0.001; Fig. 2A)
This study demonstrated that, like many calcifying ocean animals, early life-history stages of the Eastern oysters, C. virginica, are negatively affected by high levels of pCO2

Summary

Introduction

Rising levels of atmospheric CO2 have led to world’s oceans acidifying since the dawn of the industrial revolution, a process expected to continue for at least two centuries (Caldeira and Wickett, 2003). Many coastal ecosystems already experience elevated levels of CO2 (Salisbury et al, 2008; Cai et al, 2011; Hu and Cai, 2013), in part due to decomposition of the large amount of terrestrial, algal and anthropogenic organic carbon delivered to estuaries (Gattuso et al, 1998; Paerl et al, 1998; Thomas et al, 2004; Gupta et al, 2009) Animals in coastal zones are, in some cases, already subjected to acidification

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