The increasing deposition of CO2 in the oceans is causing a reduction of seawater pH in a process called Ocean Acidification (OA), posing an enormous thread to marine shelled organisms by impeding shell emergence and building. The shell is a hard biomineralized calcified structure essential for bivalve survival and it is secreted by the mantle, a tissue located in the inner shell surface. The regulation of shell building, however, is currently poorly understood. Moreover, because shell structure and composition are very diverse, it has been suggested that some bivalve species will be more susceptible than others to OA. We exposed M. galloprovincialis and C. gigas individuals, which are two leading bivalve species in aquaculture production with very different shell structures and compositions, to acidified seawater (pH 7.8) for 60 days. The mantle response of the genes associated with biomineralization was characterized and compared between the two species using a combination of biometric, functional and transcriptome studies. OA treatment decreased the shell growth in both species, and triggered a higher response in M. galloprovincialis mantle, suggesting that they adopt different gene regulation strategies to maintain and preserve the shell.
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