THE IMPACT OF CO₂ RELATED OCEAN ACIDIFICATION ON THE MOLECULAR REGULATION OF SHELL DEVELOPMENT IN EASTERN OYSTER Crassostrea virginica.

Eastern oysters (Crassostrea virginica) indigenous to the Gulf of Mexico, are crucial estuarine species in their natural ecosystem and are economically important aquaculture bivalves in the United States. Previous studies suggest that growth and development of the eastern oyster are heavily affected by the fluctuation of environmental factors including temperature, salinity, pH, pollution, etc. Due to anthropogenic activities in energy consumption, along with natural climate patterns, the global atmospheric concentration of CO₂ has dramatically increased in past decades.  This has resulted in rising dissolved CO₂ levels in seawater, ultimately leading to ocean acidification. While there is research indicating that increasing acidification of oceans could negatively impact the development of larval oysters, especially the shell development, the genomic response of oysters to this impact remains largely unknown.

To better understand the impact of CO₂ caused ocean acidification on the shell formation of the Eastern oyster on a molecular level, six previously identified bivalve shell formation related gene-encoding proteins, alkaline phosphatase (ap), calnexin (cnx), calmodulin A (CaM1), calmodulin B (CaM2), dominin (dominin) and segon (segon), were investigated in response to increased dissolved CO₂ in seawater. Expression profiles of these genes along the development of larval C. virginica were analyzed utilizing quantitative PCR (qPCR). Among these six genes, ap and cnx which were previously not identified from C. virginica were cloned using degenerated primers designed with homologous sequences from other bivalve species. The sequences of these two genes were fully characterized. Expression patterns of the six selected genes under high pCO₂ exposure were performed with primarily cultured mantle cells incubated under different percentages of atmospheric CO₂ ranging from 0.04% (control) to 10%, which resulted in pH values of cell culture medium from 7.4 to 7.0. Our results revealed that expression of CaM1 demonstrated an increase with the rise of CO₂ levels in the atmosphere, where CaM2, dominin, and segon showed similar decreasing trends with the rise of CO₂ levels. Studies on the specified roles of these genes in shell formation will contribute to a clearer representation of the impact of CO₂ stress on the development of cultured and wild populations of oysters.