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

Raised atmospheric emissions of carbon dioxide (CO 2 ) result in an increased ocean p CO 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 p CO 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 p CO 2 levels from 900 μatm (control) to 24,400 μatm. Extreme p CO 2 levels were used to determine the effects of potential leaks from the carbon capture and sequestration sites where CO 2 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 p CO 2 levels do not show significant changes in their size and shape. Likewise, the increase of p CO 2 does not affect shell hardness. However, dissolution of ontogenetically younger portions of the shell becomes more severe with the increase of p CO 2 . Irrespective of p CO 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 p CO 2 variations. Furthermore, our study indicates that naturally occurring shell mechanical property depends on the shell architecture at μm-scale. [ABSTRACT FROM AUTHOR]