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Green crabs have already invaded Washington's shorelines. Now they're heading to Alaska.

The discovery, which experts say is likely tied to warming waters because of climate change, threatens Alaskan economies, ecosystems and long-standing ways of life.
Image: European Green Crab, (Carcinus maenas), Wadden Sea, North Sea Coast, Schleswig-Holstein, Germany
A European green crab.Guenter Fischer / imageBROKER/Shutterstock

The first signs of the Alaskan invasion were discovered by an intern. 

In July, a young woman walking the shoreline of the Metlakatla Indian Community during an internship with the National Oceanic and Atmospheric Administration found a shell of a known menace in the U.S. — the European green crab. 

Two more were soon discovered. It was a day many had been dreading for years. 

“We always knew we were eventually going to see evidence of green crab,” said Dustin Winter, a member of the Metlakatla Indian Community and the program director of its fish and wildlife department. “I didn’t think it was going to happen so quickly.” 

Within a month and half, more than 80 live green crabs had been trapped along the Metlakatla shoreline, Winter said, making the community ground zero in the fight against the species in Alaska, though it’s possible other areas of Alaska have been colonized already. 

The green crab is a notorious invasive species that has reshaped U.S. ecosystems and hammered East Coast commercial fisheries for decades. The discovery of the species in Alaska represents a profound risk in a state that accounts for about 60% of the nation’s seafood harvest

They’re also almost impossible to remove. Nowhere in the world have green crabs been eradicated after they’ve established a population, scientists say. The discovery, which experts say is likely tied to warming waters due to climate change, threatens Alaskan economies, ecosystems and longstanding ways of life. 

“They’re like marine locusts,” said Genelle Winter, the tribal community’s invasive species program director, outlining how the creatures could degrade the area’s coastal shorelines, eat the Dungeness crab tribal members rely upon for meals and destroy the area’s eelgrass habitat for salmon — the foundation of the Metlakatla economy. 

Jeff Adams wades through muck to set crab traps at Nick’s Lagoon near Seabeck, Wash.
Jeff Adams wades through muck to set crab traps at Nick’s Lagoon near Seabeck, Wash.Evan Bush / NBC News

Meanwhile, efforts to thwart green crab populations elsewhere have required incredible investment and effort. Earlier this year, Gov. Jay Inslee issued an emergency proclamation to eradicate or prevent green crabs from spreading in Washington state waters. The state fish and wildlife agency assigned a crab “incident commander” and its Legislature forked over $8.5 million in emergency funding to repel its invasion.

Alaska, which has less than one-tenth of Washington’s population and more than 10 times the coastal shoreline, is preparing now for what promises to be an expensive and complicated struggle. 

“Green crab really can explode and dominate ecosystems,” said Linda Shaw, a wildlife biologist for the National Oceanic and Atmospheric Administration based in Juneau, Alaska. “The implications are huge for Alaska.”

A steady march

The European green crab has been a pest in American waters for some 200 years, but it remained an East Coast-only menace until the late 1980s, when it was discovered in San Francisco Bay, likely transported by humans in bait or in packaging. 

Green crabs are a shore species with long legs. Their bodies can grow to about four inches in width, and their color can vary. On the West Coast, these crabs can be easily confused for native species. A telltale sign for identification is that they feature five spines next to each eye.

On the West Coast, the crabs took hold in the Bay Area and then spread from there, sending larvae into ocean currents that would eventually carry them to Oregon, Washington and British Columbia. 

“Throughout the early 2000s, we would periodically have green crab spread up throughout the coast,” said Sean McDonald, a marine ecologist and associate teaching professor at the University of Washington.  

Huge pulses of green crab larvae are spread during strong El Niño conditions, when warmer surface waters dominate the North Pacific, McDonald said. 

Green crabs were first discovered along inland Washington state shores in 2016, after a prolonged marine heat wave known as the Blob. By summer 2020, they had expanded as far north as British Columbia’s Haida Gwaii, which sits near the southern tip of the Alaskan peninsula. 

“It was a steady march north,” Shaw said.“Realizing they were getting closer, it was probably inevitable they were going to show up here.” 

Like many invasive species, green crabs are likely benefiting from climate change, which often facilitates invasions. Marine heat waves, made more common by climate change, are likely boosting reproduction and distribution of green crabs, Shaw said. 

In warmer waters, larvae are more likely to survive the winter, which ramps up reproduction. Warmer waters also mean new habitat is available for green crabs. 

Federal agencies have helped to fund monitoring programs at the Metlakatla Indian Community for several years, concerned that the species would wash up and take hold on Alaskan shores. 

It’s possible that green crabs have already colonized other remote shoreline areas in Alaska. 

“Unless you’re really looking for them, you probably could easily miss that they’re there,” Shaw said. 

Sean McDonald pours hairy shore crabs — which are native to Washington state — into a bucket for observation.
Sean McDonald pours hairy shore crabs — which are native to Washington state — into a bucket for observation.Evan Bush / NBC News

And if Washington state’s efforts are any indication, deterring an invasion can be a Sisyphean task.

Population control

On a recent afternoon in late August, Jeff Adams stalked out to the center of Nick’s Lagoon, just off Hood Canal in Washington state, taking big, thigh-burning strides through a thick muck that gave off a stench of salt and sulfur. 

Adams, a marine ecologist with Washington Sea Grant who is part of a research group tracking green crabs’ spread in the state, cradled pairs of minnow and fukui traps in his hands as if carrying a football. Slung over his shoulder is a shrimp trap with a dead mackerel speared and suspended at its center. 

“The water is maybe two inches deep here,” said Adams, as his legs disappeared up to his knees in the sludge. 

Nick’s Lagoon — a pond-shaped salt marsh the size of a football field that spills in and out of Hood Canal with the ebb of the tides — is far from pristine wilderness. A rusted gear shaft stuck out from grasses on shore. Golf balls littered the lagoon bed. Another researcher, Emily Grason, reported standing on the frame of what she thought was an old car in the middle of the lagoon. It had apparently been swallowed whole by the mud in the past. 

Even so, Nick’s Lagoon is a productive ecosystem, with signs of beavers, deer and hairy shore crabs native to Washington state.

Green crabs were trapped in Nick’s Lagoon in May, marking the first time the species had been discovered in Hood Canal and the farthest south green crabs were known to have ventured in the Salish Sea, the inland body of water that connects Seattle and many other Washington port cities to the Pacific. 

The researchers, Adams, Grason and Aina Hori, a master’s student, are part of an effort to deter greens from the area. The three members of Washington Sea Grant’s crab team waded into the smelly lagoon for more than an hour, submerging 22 traps in every corner of the lagoon. They returned the next day, pulled up the traps and collected their findings. Two green crabs were among their catch. 

Years ago, the crab team began to construct a monitoring network to detect the species in Washington. Between 200 and 300 volunteers now help monitor 67 sites across the state by setting traps, documenting environmental changes and reporting invaders to the crab team on a hotline. 

So far, 15 green crabs have been caught at Nick’s Lagoon, according to Grason’s data. It’s the kind of place that could become a breeding ground if left alone. 

“What we worry about is that they raise the density where they can find each other and easily reproduce,” Grason said of the crabs. 

Preventing the crabs from reproducing in Hood Canal is paramount, Grason said, because currents here could pen in larvae.

Bags of green crabs that were collected from Washington state’s ocean shore.
Bags of green crabs that were collected from Washington state’s ocean shore.Courtesy Washington Sea Grant

“If you release green crab larvae in those places, you’re going to ratchet up your reproduction rate very quickly,” Grason said. “If you wait for them to be abundant before you do anything on it, you’ve missed your chance.”

Right now, there’s one main way to get rid of green crabs — by trapping them. The crab team’s monitoring network is designed to detect green crab, gather data and pinpoint where to focus trapping efforts. 

The Washington State Department of Fish and Wildlife now has six permanent staffers and 15 seasonal workers helping to trap green crabs, according to Allen Pleus, the incident commander for the invasion response. Tribal governments and shellfish growers are also trapping. 

As of Aug. 7, the agency and its partners had trapped 138,000 European green crab. Most of these creatures are frozen and sent to a landfill. Some are saved for science.

It’s expensive work. The state Legislature in 2022 appropriated $8.5 million in emergency funding to mount a response. In the future, Pleus said the program expects to receive about $6.1 million each fiscal year. 

Even with the burst of funding, no one expects to eradicate the green crab.

“Nobody has ever gotten rid of European green crab once it’s established large populations in its geography,” Grason said. “To the extent we can hold the line, we can buy ourselves time to figure out how to protect eelgrass beds and natural crab populations.”  

A threat to Alaska

Alaskan fisheries are among the most productive in the world. Seafood is a multi-billion dollar economy. Many indigenous communities, including the Metlakatla, rely on the region’s shorelines for shellfish. 

“The area we’re finding the crabs right now is a huge subsistence area. It’s where everybody harvests shellfish. It’s the largest population of Dungeness crab on the reservation,” Genelle Winter said. 

Threats to salmon are threats to the tribe’s future. 

“If we didn’t have a salmon fishery, I don’t know what the community would do,” Dustin Winter said. “It’s the biggest economic impact to the tribe.” 

The discovery of green crabs on the Metlakatla Indian Community’s shoreline touched off a flurry of activity in Alaska. 

Tammy Davis, the state’s invasive species coordinator, last week set off to survey other areas of southeast Alaska for signs of invasion. 

Fending the invaders off remains a daunting prospect. 

“I’m alarmed,” Davis said. “There is so much available habitat.”