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Healthy Coastal Habitats: Citizen scientists detect first invasive green crab in Washington’s inland waters

by Washington Sea Grant

UPDATE: Since publishing this story, the Washington Sea Grant Green Crab Team has found an invasive green crab (Carcinus maenas) in Westcott Bay, San Juan Island, marking the first confirmation of this global invader in Washington’s inland waters. 

“Although unexpected and unwelcome, this finding is a perfect example of how volunteers can spur positive environmental action, and it shows that the monitoring program is working as it was designed,” commented Jeff Adams, WSG marine ecologist and project manager. 

Crab Team volunteers were trained and began monitoring sites in April to detect the invasive threat and monitor Puget Sound pocket estuaries that provide ideal crab habitat. The WSG monitoring program focuses on early identification of infestations so that resource managers can take action to reduce impacts and prevent further spread.


When asked how she got involved with European green crab research, Emily Grason comments that her love affair with this small but highly adaptable predator has been a long time in the making. Grason came to the west coast in 2004 and decided to enter graduate school and pursue her studies on invasive green crab in 2008, particularly after watching Dr. Sean McDonald, one of the leads on the green crab monitoring project, present at a conference.


Fast forward a few years and Grason and McDonald’s paths cross again, this time as collaborators on the Washington Sea Grant Crab Team, a citizen science program dedicated to preemptively detecting invasive European green crab by monitoring pocket estuaries for signs of settlement. Grason had been working as a graduate student at the University of Washington’s Biology Department. Thinking green crab were no longer a threat to the region, Grason’s Ph.D. research focused on invasive snails. One day she saw an email on her department’s listserv announcing that Washington Sea Grant (WSG) was seeking a graduate researcher to work with McDonald and WSG’s Marine Ecologist Jeff Adams on green crab research. She jumped at the opportunity.

Though it’s no stranger to those living in coastal communities on both the Eastern and Western U.S. seaboards, the European green crab is a relatively new face in the Pacific Northwest. This invasive species made its first appearance on Washington coastlines in Willapa Bay, after the 1997-98 West Coast El Niño brought strong, warm currents to the region’s otherwise cold waters. In 2012, the first-known green crab colony in the Salish Sea was discovered near Victoria, sounding an alarm for Puget Sound’s valuable shellfish beds and delicate coastal ecosystems.

After a successful pilot run in 2015, Grason and the Crab Team, have been working in full swing. With an estimated 400 or more potentially suitable habitat sites in Puget Sound, the Strait of Juan de Fuca, and the San Juan Islands, Grason and the Crab Team have been hard at work training volunteers and the public, identifying the crabs, reporting and conducting extensive outreach efforts. The goal is to identify any green crab infestations early to reduce their impact and prevent further spread.

One aspect of Grason’s role on the Crab Team that she enjoys most is working with so many citizen science volunteers. “These are all adults that want to learn; they are there for the experience and eager to develop their skills and interests and are invested in the place.” Grason goes on to say, “Teaching people with that level of motivation is so much fun; I get to work with folks that are indulging their natural curiosity for places that they love and it’s wonderful to share that with people.” Green crab field research has also given her an opportunity to see a lot more of the Washington coastline and meet members of those communities. “I’ve gotten to meet residents living in threatened coastal communities who care about those places.”  Another boon of her work with Washington Sea Grant has been the opportunity to build her professional network in the local, state and regional marine conservation community.

The green crab project has even had some overlap with Grason’s graduate research. As it turns out, the invasive Asian mud snail is present at some of the green crab sites. The species is not one many people are interested in because it has little economic impact, but it could prove to be a good food source for the green crab. Volunteers have been collecting snail density information while monitoring for crabs. This data that will allow Grason to explore seasonal patterns, an analysis she would not have been able to conduct otherwise.

So far this summer there has been no evidence of green crab infestation in any inland Washington waters, but the Crab Team is still staying busy. Grason recently returned from a visit to Willapa Bay where she was experimenting with different crab baits. But even at this coastal monitoring site where crabs have been abundant in the past, they didn’t find many green crabs, and the few crabs they did find were from the previous year’s cohort, meaning relatively few young green crabs were washed in on this year’s recent El Nino currents.

Although the coast is clear for now, active monitoring will continue through September and resume in April. The team hopes to report findings back to their many dedicated volunteers by end of the year. Since she recently defended her dissertation, Grason will soon be exploring next steps and she’s considering staying with the project into the next monitoring season.

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