We propose to investigate effects of seawater acidification on the settlement success of estuarine bivalves. Bivalve populations living in bays and estuaries are subject to fluctuations in temperature, salinity, and water chemistry, and the chemistry of seawater has long been suspected to have an important role in the success or failure of bivalve recruitment. Estuarine chemical variability includes coupled changes in dissolved oxygen (O2), pCO2 and pH, and these local carbonate chemistry fluctuations (“estuarine acidification”) are often large relative to the anticipated 21st century global changes due to rising anthropogenic CO2 (“ocean acidification”). We hypothesize that if low-pH or low-O2 events occur during the seasonal settlement window of a bivalve species, recruitment will be inhibited. This process may underlie the well-known but poorly-understood occurrence of ‘bad years’ for bivalve recruitment. To investigate this hypothesis, we propose a two-year study in Waquoit Bay to (1) document the high-frequency (diel and day-to-day) variability in water chemistry (O2, pH, and aragonite saturation state (Ω)) during the July/August settlement period of local bivalves and identify the causes of that variability; and (2) assess the effect of low-oxygen / low pH / low saturation state events on bivalve settlement success. Larval supply and predator activity will also be assessed to help determine the mechanism of any observed correlation between chemistry and settlement.
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