Initiation of bivalve shell calcification under ocean acidification: integrating insights from shell to cell

The formation of initial bivalve shell is sensitive to ocean acidification, encoding the basis of shell formation and environmental information. Here, we demonstrated how the initial shell building processes were affected under various acidified conditions. With decreasing pH, larvae showed smaller shells and higher incidences of deformity. Shell elemental and isotopic profiles suggested that larvae almost exclusively used seawater dissolved inorganic carbon to calcify and exhibited diminished ability to maintain the calcifying fluid homeostasis. Compared to those reared at pH_NBS 8.1, larvae exposed at pH_NBS 7.7 downregulated the expression of genes related to transport of calcification substrates and regulation of carbonate chemistry, all of which were subsequently upregulated at pH_NBS 7.4. This integrated finding advances the application of sclerochronology by providing insights into the initial shell formation, a crucial phase that is overlooked in sclerochronological studies, particularly in how environmental stressors affect the interpretation of geochemical proxies in adult shells.