Keywords: Species and food webs, Invertebrates, Nearshore habitat, Green crabs, Salish Sea, Implementation Strategies, Invasive species, Salish Sea Currents magazine

The state's stay-at-home order has halted much of the field research that would normally be underway in Puget Sound this spring, but a small group of scientists and volunteers have been able to continue their search for an invading marauder along the shoreline. Their work has been classified as critical by the state.


This is a story of a region struggling to withstand a menace that recently arrived—one that, by the time you realize it is here, may have already spread beyond any hope of containing it. Now, officials at all levels of government scramble to detect it as quickly as they can, which may be the only way to forestall the most devastating of its consequences. Whether or not they succeed will have profound implications both for local lives and livelihoods.

We refer, of course, to the European green crab. Why? Did you think we were talking about something else?

It is late in the afternoon in late April, and I am sitting on a narrow strip of land near Lacey, Washington. The strip separates a small, brackish lake from Butterball Cove, an inlet that is part of Puget Sound proper. A few feet from me—always more than six feet, just to be clear — Emily Grason and Amy Linhart are hauling over two large mesh traps, called Fukui traps, from the lake’s nearshore, where they have sat since yesterday evening, baited with pieces of mackerel. One trap is empty, but the bottom of the other swarms with small, wriggly things.

“Okay, let’s get this open,” Grason says. A marine ecologist with Washington Sea Grant (WSG), and program manager of the WSG Crab Team, she pops the trap’s central hinge, spilling its contents into a white plastic tub. A couple of dozen small shore crabs tumble out and scuttle against the tub’s walls. Grason adds some water and swills the contents while Linhart stands off to her side on tiptoe, trying to peer in.

“These look like they’re all hairy,” Grason says, meaning hairy shore crabs, a species common to the area. She transfers half the crabs to a second tub, which she hands to Linhart, the Crab Team Coordinator. Both biologists get out calipers and start to measure the width of the crabs’ carapaces one-by-one. The blue gloves they wear give the shore crabs something to grab, which they do; their tenacity makes measuring them tough. “It’s a pinch-or-be-pinched world,” Grason says as she waits for one crab to loosen its grip. She and Linhart call out widths and crab sexes to Gail Trotter, who is recording data. Trotter is in her mid-50s and lives on the bluff that overlooks the cove. For the past few years, she has surveyed Butterball Cove for the presence of European green crabs as a volunteer with the community science project Grason heads.

The Washington Sea Grant Crab Team (Emily Grason, Amy Linhart, and Gail Trotter) measures crabs captured at Butterball Cove near Lacey, Washington. Photo: Eric Wagner

The Washington Sea Grant Crab Team (Emily Grason, Amy Linhart, and Gail Trotter) practices social distancing while measuring crabs captured at Butterball Cove near Lacey, Washington. Photo: Eric Wagner

I sit apart, watching the three of them work. Between the gloves and the masks and the peculiar socio-viral-magnetic field that keeps everyone a polite-but-precise distance from one another, there is something a little surreal about this exercise of community science in the midst of a pandemic. But to not be here at all would be to yield the area to the green crabs, potentially at least, and that is not an option. [Editor's note: Members of the WSG Crab Team were designated as "critical employees" by Washington Sea Grant, allowing them to continue their field research under strict conditions established by the state. Individual volunteers who have elected to participate in sampling "are designated as individuals performing a critical service," according to WSG Crab Team manager Emily Grason.]

A worldwide menace

The European green crab is considered one of the worst invasive species in the world. Although native to Europe and northern Africa, the species has spread far, often via ballast in ships, or concealed among the seaweed packed around lobsters and oysters on their way to market. The crabs are now found in coastal habitats in South Africa, Brazil, Australia, Japan, and elsewhere.

Their history in North America begins on the east coast in the early 19th Century. There they cause the periodic collapse of the soft-shell clam industry in New England, costing tens of millions of dollars. In southeastern Canada, their habit of digging and burrowing has decimated eelgrass beds, leading to declines in fish abundance. They may serve, too, as an intermediate host for a parasitic worm that affects shorebirds.

Three views of the European green crab. Photos: Kelly Martin and Jeff Adams/WSG

The European green crab (Carcinus maenas). Photos: Kelly Martin and Jeff Adams/WSG

As such, wildlife officials along the North American west coast went on high alert when green crabs were found in San Francisco Bay in 1989. But the crabs stayed put, more or less, wreaking local havoc on native clams and shore crabs until 1998, when, during an El Niño event, their larvae rode unusually warm currents as far north as Vancouver Island, Canada. They were subsequently detected in Willapa Bay and Grays Harbor on Washington’s outer coast, but their numbers were low and did not seem to be spreading further, so Washington state officials ended monitoring efforts after a few years.

A bucket of European green crabs (Carcinus maenas). Photo: W.carter (CC BY 1.0)

A bucket of European green crabs. Photo: W. Carter (CC BY 1.0)

Then, in 2012, biologists with the Canadian government found a population of green crabs had established in the Sooke Basin on the southern tip of Vancouver Island—well within the Strait of Juan de Fuca and in easy striking distance of Puget Sound. This was enough to convince state officials of the need for a wide-scale monitoring program for the 1,800 miles of coastline on Washington’s inland waters.

A wake-up call

The work of watching for crabs now falls in large part to more than two hundred people who serve as volunteers with the WSG Crab Team. Every month during the spring and summer, volunteers set traps to survey fifty-six sites throughout Puget Sound and the Salish Sea. To date, surveys either by WSG volunteers or one of several federal, state, or tribal partner agencies have found evidence of European green crabs scattered across the northern coast of the Olympic Peninsula, the San Juan Islands, Whidbey Island, and other parts of the Salish Sea.

Emily Grason, program manager for WSG Crab Team, works with volunteers to stop the green crab invasion in Puget Sound. Photo: Sean McDonald/UW

Emily Grason, program manager for WSG Crab Team, training volunteers to help stop the green crab invasion in Puget Sound (prior to COVID19 and social distancing requirements). Photo: Sean McDonald/UW

Although no population seems to have established so far, there are worrying signs. Last September, the Crab Team caught seventeen green crabs over the course of two days at Drayton Harbor, near the U.S. – Canada border. It was the largest number of crabs ever caught in any one area of Washington’s inland shoreline. “Capturing that many crabs so quickly was definitely a wake-up call of a sort,” says Allen Pleus, a biologist with the Washington Department of Fish and Wildlife. “We have emergency measures now at Drayton.” The Lummi Department of Natural Resources has similar measures at nearby Lummi Bay.

The finding also caused ripples of worry to spread farther south.  “For us, obviously we want to avoid the destructive consequences of a big infestation,” says Todd Woodard, the director of natural resources for the Samish Indian Nation in Anacortes, on Fidalgo Bay. Fidalgo Bay has a lot of eelgrass beds — prime habitat for crabs, salmon, and other species critical to the Samish. Biologists with the tribe have so far not caught any live green crabs at their one survey site, although a molted shell was found; and live crabs have been caught in Padilla Bay. “These things can really take hold,” says Matt Castle, a field technician on the project. “Some of the videos we’ve seen from the east coast, they show crabs erupting out of the seagrass like in a horror movie. We really don’t want to see that here.”

But the coronavirus pandemic, and Governor Jay Inslee’s stay-at-home order have complicated this year’s management effort somewhat. In the past, biologists have found that the most effective time to trap for green crabs is in April and May. “That’s when we get the most bang for our buck,” Pleus says. But at the time of writing, state government workers are not allowed out to do surveys until a safety protocol has been approved. Similarly, biologists with the Samish are trying to figure out the most prudent way to continue their surveys. “We worry about the crabs making inroads while we’re not out there,” Woodard says.

Survey effort

A sparer survey effort is not the only consequence of the coronavirus pandemic for the Crab Team. In mid-April, organizers cancelled the 2020 Salish Sea Ecosystem Conference. “It was a real disappointment,” Grason says. Not only had she and her colleagues organized a session devoted to green crabs, but the conference would have provided them all with a rare chance to all be in the same room at the same time so they could plot strategy and new lines of research.

Most of the biologists concerned with the European green crab live in Washington, but not all of them. One who could not attend the conference was Carolyn Tepolt, a research scientist at the Woods Hole Oceanographic Institution in Falmouth, Massachusetts, who has been collaborating with Grason for several years.

Tepolt studies the genetics of biological invasions. For her, the European green crab provides a fascinating case study. “Ecologically, it’s really unfortunate they’re finding green crabs in Salish Sea, but from an evolutionary biology perspective, this is a fascinating opportunity,” Tepolt says. It is rare, she tells me, for scientists to catch an invasion as it is expanding. “Usually,” she says, “we find them afterwards when they’re in high numbers. The fact that Emily’s group has been doing such amazing monitoring means they’re able to track the expansion and find crabs in places where they haven’t become established, where they’re beginning to come in.”This means that Tepolt can watch a sort of experiment unfold in real time: What happens to a small population as it expands in time and space and, possibly, abundance? Is there enough dispersal to keep populations connected? And how quickly are the green crabs able to adapt to new environments?

Story map: European green crab in Puget Sound

A broad collaboration of volunteers, agencies, and tribes are working together to keep invasive European green crabs at bay in Washington state. This story map was produced by the Encyclopedia of Puget Sound and the Puget Sound Institute in collaboration with the Washington Sea Grant Crab Team. 

In this, the dynamics of European green crabs on the west coast differ from those of their kin on the east coast. “Each has its own invasion pattern,” Tepolt says. “On the east coast we have at least two introduction events, but on the west coast we’re pretty sure it was only one. Also, the spread on the east coast was relatively slow.” But quicker though the green crabs may have spread on the west coast, their coverage is more discontinuous, with isolated pockets of crabs in protected bays and estuaries, rather than a carpet over everything. This, she says, may be due to differences in the oceanography between the Atlantic and the Pacific, as well as the nature of the two coastlines. “The west coast is a harsher environment in a lot of ways, with a more intact native community. So it may be harder for the crabs to get a foothold.”

Tepolt was looking forward to coming to Vancouver and sharing some data — “There are really intriguing signs that green crabs may have an evolutionary mechanism that lets them adapt to local temps really quickly,” she says — while also meeting some new collaborators. Now, all of that is put on hold. “But,” she says, “there’s always the next one.”

In the meantime, members of the Crab Team will continue to survey where they can when they can. Right now, about half of Grason’s volunteers are out, and more are expected to join once the state Stay At Home order lifts at the end of May.

Washington Sea Grant Crab Team Coordinator Amy Linhart empties crabs from a minnow trap into a plastic tub at Butterball Cove. Photo: Eric Wagner

Washington Sea Grant Crab Team Coordinator Amy Linhart empties crabs from a minnow trap into a plastic tub at Butterball Cove. Photo: Eric Wagner

“We brainstormed ways for volunteers to work while maintaining social distance,” Grason says. The survey at Butterball Cove is the first she and Linhart have done this year, and so this has been their chance to test how things will go for the foreseeable future: The gloves, the masks, the six feet at all times. “So far, so good?” Grason says at one point.

Still, there will be consequences. Near the end of the survey, when Linhart is dumping crabs from the last trap into one of the plastic tubs, Grason suddenly says, “Oop! A crab got out!”

Linhart immediately starts looking here and there around her. “I don’t see it!” she says.

“Oh, it’s already gone,” Trotter says with a tone of resigned experience. “Once they get out, those suckers can move so fast.”

“That’s why we like to have two people do the dumping,” Grason says while Linhart combs through the grass around her to no avail. “So if a crab gets away, the second person can catch it. But we can’t do that now because…” She trails off and shrugs.

Linhart sinks to her knees and looks crestfallen. “If that was a green crab, I’m gonna feel so bad,” she says.

“It probably wasn’t a green crab,” Grason assures her kindly. “Don’t lose any sleep over it.”


About the author: Eric Wagner writes about science and the environment from his home in Seattle, where he lives with his wife and daughter. His writing has appeared in Smithsonian, Orion, The Atlantic and High Country News, among other places. He is the author of "Penguins in the Desert" and co-author of "Once and Future River: Reclaiming the Duwamish." His most recent book is "After the Blast: The Ecological recovery of Mount St. Helens," published earlier this year by University of Washington Press. He holds a PhD in Biology from the University of Washington.

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