Use of eelgrass as a mitigation strategy for effects of ocean acidification on oyster farms

Principal Investigators: Jeff Davidson & Maya Groner
Co-Investigators: John Bucci, Colleen Burge, Carolyn Friedman & Sandy Wyllie-Echeverria

Climate change is affecting the health of marine organisms globally. Our ability to mitigate climate change impacts is an important step in limiting future impacts on ecosystems and the fishers and culturists they support. Ocean acidification, or the decrease in seawater pH, is a threat to shellfish such as the Pacific oyster. In contrast, seagrasses such as eelgrass may benefit from the increased organic carbon available in acidified ocean environments, and can create local areas of pH refugia. Oysters may, through filtration, improve the health of eelgrass by removing the pathogen that causes eelgrass wasting disease. One potential mitigation strategy to improve the health of both oysters and eelgrass is growing them together.

In order to test the potential benefits of an oyster-eelgrass partnership, we conducted a laboratory study comparing monoculture and co-culture of juvenile Pacific oysters and eelgrass under three C02 conditions (400, 800, and 1600 ppm). We exposed half of the tanks to the slime mold pathogen (L. zosterae) that causes eelgrass wasting disease. In low pH (acidic) conditions, the proportion of diseased eelgrass leaves decreased more than in high pH conditions. Together, increased day-time photosynthesis in co-cultured eelgrass and Pacific oysters may have positive effects on oyster growth. Based on observations of diseased leaves, eelgrass health may also benefit from low pH conditions.