A volunteer network to protect the Salish Sea

No one knows exactly how European green crabs might impact Washington’s inland waters, but their destructive track record calls for action. In 2015, the Washington Department of Fish and Wildlife entrusted Washington Sea Grant with leading a multi-partner monitoring effort to protect the Salish Sea.

Many local marine habitats are vulnerable. European green crabs can thrive in conditions that are less hospitable to native crustaceans like Dungeness crabs. Their adaptability to varying levels in temperature, oxygen and salinity makes the species almost perfectly suited to colonize new environments.

“They are amazing survivors. I’ve seen them occupy habitats that defy explanation,” says McDonald. He, too, appreciates the diminutive crabs, even as he and Grason work to stop them.

Crab Team volunteers come from a range of professional backgrounds — no science experience required. Each small team monitors a site from April through September. Over two days, they set and check traps for European green crabs, and survey sites for molts: the exoskeletons (hard shells) that crabs shed as they grow.

Monitoring to head off a green crab invasion

Invasive species often spread until they’re too numerous to control. To combat this trend, Crab Team and the Washington Department of Fish and Wildlife use a monitoring model called early detection and rapid response. Its premise is simple: Find invasive European green crabs before they have a chance to breed or spread.

“We have a unique opportunity to put in a relatively small amount of effort in a very targeted way and do something different, change what seems inevitable,” Grason says.

When Crab Team began in 2015, no one expected to find any invaders. Although green crabs had lived for years in British Columbia’s Sooke Inlet, the Salish Sea’s colder temperatures and current flow kept them at bay.

Then, in 2016, everything changed.

Crab Team volunteers found a single European green crab on San Juan Island.

Soon after, Padilla Bay National Estuarine Research Reserve staff discovered another. The ensuing rapid response unearthed three more. In 2017, Crab Team volunteers, Washington Sea Grant scientists and the U.S. Fish and Wildlife Service trapped 96 European green crabs on Dungeness Spit in the Strait of Juan de Fuca. Other individual crabs have been found at Sequim Bay, Makah Bay and on Whidbey Island.

Potential risks to Dungeness crab, shellfish and salmon habitat

It’s hard to predict the exact impact that European green crabs could have in Washington. For invasive species experts like Grason, the possibilities are both intriguing and concerning.

“It’s like watching a really good, dramatic TV series,” Grason says. “Every invasion is different. This combination of species and environmental conditions has never happened before anywhere on the planet, and you don’t know how it’s going to play out.”

Even so, scientists have ideas about what’s at risk based on the crabs’ well-documented invasion history elsewhere.

In Maine, the crabs have decimated eelgrass beds in their relentless search for food and have contributed to the soft-shell clam industry’s decline. Washington’s eelgrass beds provide critical habitat for salmon, Dungeness crab and other iconic species that support entire marine-based industries.

Unprotected shellfish beds on public beaches and tribal nations’ tidelands are also vulnerable. If the crabs begin reproducing in the Salish Sea, harm could ripple up the marine food web to people who eat seafood — and to workers, business owners and communities.

Jeff Adams
Crab Team project lead; marine ecologist, Washington Sea Grant.

More about Jeff

McDonald cautions that much remains unknown. “I’m not sure we’re very good at imagining the worst-case scenario,” he says. “They’ve been on the East Coast for 200 years, but we didn’t expect the problems they’ve created in Maine and the Canadian Maritimes over the past 10.”

It’s difficult to be on the front lines against an invasive species that keeps launching new assaults. What keeps Grason going? For one thing, the program seems to be working — Crab Team keeps finding the creatures before their numbers grow. Just as important, the program is creating a network of passionate volunteers whose enthusiasm catches on in their communities.