Impact of high pCO2 on shell structure of the bivalve Cerastoderma edule

Raised atmospheric emissions of carbon dioxide (CO2) result in an increased ocean pCO(2) level and decreased carbonate saturation state. Ocean acidification potentially represents a major threat to calcifying organisms, specifically mollusks. The present study focuses on the impact of elevated pCO(2) on shell microstructural and mechanical properties of the bivalve Cerastoderma edule. The mollusks were collected from the Baltic Sea and kept in flow-through systems at six different pCO(2) levels from 900 mu atm (control) to 24,400 mu atm. Extreme pCO(2) levels were used to determine the effects of potential leaks from the carbon capture and sequestration sites where CO2 is stored in sub-seabed geological formations. Two approaches were combined to determine the effects of the acidified conditions: (1) Shell microstructures and dissolution damage were analyzed using scanning electron microscopy (SEM) and (2) shell hardness was tested using nanoindentation. Microstructures of specimens reared at different pCO(2) levels do not show significant changes in their size and shape. Likewise, the increase of pCO(2) does not affect shell hardness. However, dissolution of ontogenetically younger portions of the shell becomes more severe with the increase of pCO(2). Irrespective of pCO(2), strong negative correlations exist between microstructure size and shell mechanics. An additional sample from the North Sea revealed the same microstructural-mechanical interdependency as the shells from the Baltic Sea. Our findings suggest that the skeletal structure of C. edule is not intensely influenced by pCO(2) variations. Furthermore, our study indicates that naturally occurring shell mechanical property depends on the shell architecture at mu m scale. (C) 2016 Elsevier Ltd. All rights reserved.