| Summary: | The global process of ocean acidification caused by the absorption of increased atmospheric carbon dioxide decreases the concentration of carbonate ions and reduces the associated seawater saturation state (ΩCaCO3) - making it more energetically costly for marine calcifying organisms to build their shells or skeletons. Bivalves are particularly vulnerable to the adverse effects of ocean acidification on calcification, and they inhabit estuaries and coastal zones - regions most susceptible to ocean acidification. However, the response of an individual to elevated pCO2 can depend on the carbonate chemistry dynamics of its current environment and the environment of its parents. Additionally, an organism's response to ocean acidification can depend on its ability to control the chemistry at the site of calcification. Biotic and abiotic stressors can modify bivalves' control of calcifying fluid chemistry - known as extrapallial fluid (EPF). Understanding the responses of bivalves - which are foundation species - to ocean acidification is essential for predicting the impacts of oceanic change on marine communities. This dissertation uses a culturally, ecologically, and economically important bivalve in the northwest Atlantic - the Eastern oyster (Crassostrea virginica) - to explore the effects of environment and species interactions on responses to elevated pCO2. Chapter 2 describes a field study that characterized diurnal and seasonal carbonate chemistry dynamics of two estuaries in the Gulf of Maine that support Eastern oyster populations. The estuaries were monitored at high temporal resolution (half-hourly) over four years (2018-2021) using pH and conductivity loggers. Measured pH, salinity, and temperature were used to calculate carbonate chemistry parameters. Both estuaries exhibited strong seasonal and diurnal fluctuations in carbonate chemistry. They also experienced pCO2 values that greatly exceeded current atmospheric carbon dioxide levels and those projected for the year 2100. Chapter 3 describes a ...
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