On November 4, 2025, a group of over twenty volunteers joined Puget Soundkeeper to assist the Washington Department of Fish and Wildlife (WDFW) with their bi-annual Mussel Watch project. This is a study to analyze the magnitude of organic, metal, and chemical contamination at nearshore environments across Puget Sound. These toxic substances can cause harm to aquatic ecosystems and pose a risk to aquatic wildlife and the people who consume them. Monitoring the toxic contaminants in Puget Sound not only allows us to define areas of contamination in the nearshore environment that may not be as obvious (areas that face contamination from nonpoint pollution sources, such as stormwater runoff) but also guides the steps and progress of recovery efforts.
Why Mussels?
Mussels are excellent filter feeders and constantly filter-out water for food, meaning they also happen to accumulate pollutants and toxins that are in the water. As they take in large amounts of seawater, contaminants concentrate in their tissues until they reach equilibrium with the environment they inhabit. Because mussels do not have a liver, they have limited capacity to metabolize these contaminants and typically retain concentrates in their tissues for approximately three months (WDFW Toxics Biological Observation System, 2025; Langness, 2024). This makes mussels the perfect creatures to determine pollution exposures in our nearshore ecosystems!
To confirm consistency across surveys, WDFW sources aquaculture-grown mussels (Mytilus trossulus) donated by Penn Cove Shellfish, LLC on Whidbey Island. These mussels are distributed to cage deployment teams and placed in designated monitoring sites. Using transplanted mussels rather than wild mussels reduces site limitations, enables the measurement of specific biological metrics, and ensures we are starting with a standardized baseline (a clean slate)!
The Process
The process all starts with the locations. To obtain a vast set of data, mussel cages are deployed all around Puget Sound at over 80 sites with the help of WDFW, state and local agencies, and community partners like Puget Soundkeeper. Each group is assigned to a certain number of cages and site locations. Puget Soundkeeper was provided with eight cages this year to be placed along King County shoreline, spanning from Burien to the south and Magnolia to the north.
Puget Soundkeeper is responsible for coordinating with homeowners (if the mussel cage deployment involves entering private property), rallying up a team of incredible volunteers to help nestle the cages into the beaches, and providing the training to ensure volunteers are prepared to skillfully and safely install the cages.
Staff prepare all necessary tools and materials for cage deployment in advance, including retrieving the mussels from WDFW earlier on the day of the event, to ensure they remain cold. Volunteers and staff meet in the evening for a training that includes how to locate cage sites and how to properly install the cage on the beach. Installation involves anchoring the cages using rebar stakes and helical screw anchors, with cinder blocks added to high activity sites. Following the training, teams of three to five volunteers are sent to one of the eight cage locations to install the cages and complete datasheets documenting coordinates, site conditions, and weather observations.
After three months, volunteer teams are sent out again to retrieve the mussel cages and return the mussels to WDFW to complete the analysis of the tissue samples for contaminants. They are analyzed for a list of legacy contaminants including PAHs, PCBs, PBDEs, and DDTs, which have been identified as important monitoring chemical classes due to their risk to human/aquatic species health, their persistence, and geographic magnitude (WDFW Toxics Biological Observation System, 2025). In the past, WDFW has allowed volunteers to observe and join the laboratory process; scheduling is currently in the works for that to occur again this winter.
Mussel retrieval is set to January 29, 2026. Interested in supporting the retrieval or getting involved in the next bi-annual deployment? Reach out to Nani Welsh at naniw@pugetsoundkeeper.org
Sources:
WDFW Toxics Biological Observation System (TBiOS). (2025, August 13). Biomonitoring of contaminants in the Puget sound nearshore. ArcGIS StoryMaps. https://storymaps.arcgis.com/stories/992bcde65ce8407b887318754a91929e
Washington Department of Fish and Wildlife, & Langness, M. (2024, January 5). Mussel Watch Monitors Toxics in Puget sound. Medium. https://wdfw.medium.com/mussel-watch-monitors-toxics-in-puget-sound-2d59212cd3f4