Ocean Acidification Thresholds for Eastern Oysters

Ocean acidification (OA), a global anthropogenic stressor, may irrevocably damage estuarine ecosystems and their services. Oysters, including the eastern oyster Crassostrea virginica, respond negatively to conditions of OA, reaching physiological thresholds – conditions of seawater chemistry beyond which they are not able to grow or reproduce. We used laboratory experiments to quantify ecologically-relevant thresholds for OA impacts on C. virginica. Rates of oyster growth, calcification, respiration, filtration, excretion and condition index were measured under four OA scenarios for two size classes of oysters. Results were combined with a literature synthesis to parameterize formulations for the effect of pH on oyster vital rates in the coupled oyster-ecosystem model EcoOyster. EcoOyster was then coupled with the seagrass bio-optical model GrassLight to explore the potential for seagrass metabolism to mitigate the impacts of OA on oyster restoration and aquaculture. On short time scales (hrs to days), seagrass metabolism has the potential to alter seawater chemistry sufficiently to mitigate OA impacts on oysters and possibly induce beneficial changes in carbonate chemistry conditions. Synergistically, oyster filtration has the potential to clarify estuarine waters, thereby increasing light penetration and seagrass photosynthesis that further buffer the impacts of OA on oyster metabolism. Simulations are being conducted to quantify these interactions between oysters and seagrasses in order to assess the potential for co-restoration to mitigate OA thresholds for oysters. The final coupled model will ultimately be translated into decision-support tools to inform restoration planning and aquaculture operations.