In early November, teams of Puget Soundkeeper volunteers bundle up and head to Seattle-area beaches during a late-night low tide. They’ll hammer in cages of native mussels for our annual mussel monitoring program. Why? Because mussels are a great tool for figuring out what’s in our water. These cages, retrieved in February, are part of the Puget Sound Mussel Monitoring program. The Washington Department of Fish and Wildlife coordinates the program, which is ongoing since 1986. It includes a network of state, county, and city agencies, tribes, marine resource committees, and other groups.

Why Mussels?

Mussels are prolific filter feeders that can filter anywhere from 20–50 gallons of water each day. Because of this, they perform an important ecosystem service—they clean our water! However, this also means they accumulate the chemicals present in their aquatic ecosystem in their tissues. Mussel digestive systems are relatively primitive, lacking a functioning liver. They cannot metabolize contaminants and instead accumulate them unchanged in their tissues.

This is bad news for mussels, but good news for science. Mussels accumulate contaminants until they reach equilibrium with their environment. This usually takes 60–90 days, the same amount of time our mussel cages are placed. Mussels provide a comprehensive look at which pollutants are present in a body of water over a period of time. This method is more robust than taking a sample on a single day, when conditions may vary. It’s also more sensitive to low levels of contaminants that may otherwise go undetected.

Results and Goals

Puget Soundkeeper coordinates volunteers for the Seattle sites, while Fish and Wildlife analyzes our results. The 2019/20 survey report is pending, but the 2017/2018 survey revealed the following:

Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethanes (DDTs)–organic contaminants known to cause cancer and other health impacts–were among the top four organic contaminants found in mussel samples collected throughout the state. All seven of the metals measured in this study–aluminum, arsenic, cadmium, copper, lead, mercury, and zinc–were also detected in the mussel samples.

The 2021/20222 study continues to support Stormwater Action Monitoring (SAM) program efforts to measure stormwater impacts on the environment and evaluate the effectiveness of stormwater management actions. Over the long term, this project helps Soundkeeper and our partners monitor and understand changes in Puget Sound water quality.