Determining Whether Native Eelgrass and Pacific Oysters Synergistically Enhance Their Environments

Researchers assess whether Zostera marina and Crassostrea gigas are potential partners in a changing ocean.

Principal Investigator

Carolyn Friedman, University of Washington, School of Aquatic and Fishery Sciences

Co-Principal Investigators

Meg Chadsey, University of Washington, Washington Sea Grant

Colleen Burge, University of Maryland Baltimore County

Drew Harvell, Cornell university

Brady Blake, Washington Department of Fish and Wildlife


Eelgrass wasting disease (EGWD), which may be caused by the pathogen Labyrinthula zosterae, negatively affects eelgrass beds along the West Coast. In the Pacific Northwest, eelgrass and shellfish cultures often grow in the same place. This project focuses on a potential benefit of co-culture: filtration services of oysters to improve the health of eelgrass beds, potentially reduce pathogen loads, and improve local water quality. Different strains of Labyrinthula were analyzed for virulence and responses under different conditions (i.e. temperature, pH, and shellfish presence) were considered. The results will provide the shellfish industry, tribes, resource managers, and the public with key diagnostic and genomic resources that will promote sustainable shellfish culture in Washington State.

Research Updates


Eelgrass plays a critical role in Washington’s marine ecosystems, as eelgrass beds stabilize shorelines and provide food, shelter and habitat for organisms, including juvenile salmon and herring. However, eelgrass is declining in many areas of the state, and eelgrass wasting disease (EGWD)—caused by the pathogen Labyrinthula zosterae—is a possible culprit. Washington Sea Grant-funded researchers began an investigation on the threat of EGWD to local eelgrass, how this threat may change with warmer and acidified waters, and whether shellfish living within eelgrass beds could help mitigate the situation.

Results Thus Far

Of the 14 Labyrinthula strains investigated, 4 did not produce signs of EGWD, 3 resulted in low-to-moderate infections, and 7 produced severe infections evidenced by widespread tissue damage. The researchers discovered that an individual eelgrass does not need to be in contact with another individual in order to spread the disease, suggesting the pathogen can spread through the water column. Temperature makes a difference: widespread infections occurred more quickly at 15 than at 7.5 degrees Celsius. The surveys showed EGWD prevalence levels exceeded 65 percent at all but one of the 10 sites, indicating widespread, high levels of the disease in Washington.