Pacific (Crassostrea gigas) and Olympia (Ostrea lurida) Oyster Shell Dissolution Rates in Yaquina Bay, OR

A large focus of ocean acidification research has examined responses in biocalcification rates with far less on dead shell dissolution. Oyster reefs require a positive shell budget; the rate of shell generation must outpace shell loss. Shell loss can occur due to two primary environmental drivers: chemical dissolution and burrowing organisms (and presumably the interaction of the two). Ocean acidification lowers calcium carbonate saturation state and thus increases shell dissolution rates, with potentially greater effects in the poorly buffered estuarine habitats where oysters are found. Few studies have quantified near-term whole shell dissolution rates. We conducted laboratory and field studies to quantify whole shell degradation rates of Ostrea lurida and Crassostrea gigas. Our field studies tracked individual shell mass loss for more than a year across an estuarine gradient, with measurements taken weekly to monthly to capture seasonal dynamics. Laboratory based studies examined the sensitivity of shell dissolution to changes in carbonate chemistry across four treatment levels of saturation state. The field study produced increased dissolution during the wet season and generally increased dissolution rates up estuary, corresponding to lower alkalinity. During the wet season, an average dissolution rate of -3.76% was seen at the site with lowest alkalinity, -0.53% at the site with intermediate alkalinity, and 0.09% at the site with highest alkalinity. However, in the dry season slightly higher dissolution rates were observed at the site proximate to the ocean compared to the intermediate site, likely due to elevated CO₂ during upwelling events. Additionally, we will investigate differences in dissolution rates between O. lurida and C. gigas.