The National Oceanic and Atmospheric Administration (NOAA) calls European green crabs one of the most invasive marine species in the world. They are widely blamed for the collapse of the softshell clam industry on the East Coast. Now, the species has been wreaking havoc up the west coast of North America.
“We’re kind of on the front lines with the invasion here,” said Ian Hudson. Hudson coordinates the Metlakatla Indian Community’s green crab program.
Metlakatla is the southernmost community in Southeast Alaska. Locals there had been worried about green crabs for years. The tiny, invasive crabs were first found in San Francisco in 1989 and have been marching north ever since. States like Oregon and Washington have spent millions of dollars trying to protect their lucrative shellfish industries but still, green crab populations there are booming.
In 2022, the community’s worst fears were realized. They found three of the crabs’ shells on their shores. Now, two years later, Hudson said finding shells in the summertime is “basically a daily affair.”
They continued to find more and more of the invasive crabs, but Hudson said in September of this year, it was especially bad.
“We had a giant spike where we found nearly 1,000 in a week-long period,” Hudson said.
He no longer means just shells. He means live crabs. In total this year, Hudson and his team removed nearly 1,500 of the invaders from the ecosystem.
Just getting warmed up
Barbara Morgan, a professor with the University of Alaska Southeast, said the big spike in crabs that Metlakatla saw may have something to do with it being an El Niño year. El Niño is a recurring weather pattern that makes for warmer water temperatures in parts of the Pacific Ocean. As Morgan put it, green crabs love the warmer temperatures and in an increasingly warming world, even colder parts of the state may not be safe from the invasion.
“The thought is that with climate change, that’s going to actually help them spread,” Morgan explained. “They have a really wide temperature tolerance but eventually they will reach water far enough north that it’s too cold for them to reproduce, and so they will not be able to expand further beyond that point. But warmer water from an El Niño or from climate change will help them spread further, reproduce more.”
The crabs are especially sensitive to temperature at the larval stage. So when the water is warmer, more baby crab larvae survive and are carried outward on ocean currents, producing more cohorts of crabs.
Other places that have been overrun by the crabs further south have seen massive declines in eelgrass.
“Eelgrass is keystone to our nearshore habitat,” said Tammy Davis, the Invasive Species Coordinator for the Alaska Department of Fish and Game.
“It’s a nursery habitat for salmon. It’s a nursery habitat for juvenile Dungeness [crabs]. It’s a key habitat for spawning herring. Bivalves, gastropods, other introverts, and other types of crustacean use that eelgrass habitat because it provides protection,” she said.
Davis said European green crabs are hungry. They eat clams, oysters, scallops, and can outcompete and decimate crab populations like the locally prized Dungeness crabs. In Washington state and British Columbia, there have been reports of them eating salmon eggs. In 2022, Washington’s governor, Jay Inslee, declared a state of emergency for the green crab invasion.
“It’s not just that we’re worried about the sea grass. We’re really worried about that whole ecosystem,” Davis said.
Getting the band together
Jasmine Maurer works for the Kachemak Bay National Estuarine Research Reserve in Homer.
“There are a lot of things we don’t know yet, and we also do know many ways that they can negatively impact things that are important to us,” Maurer said.
She added that it isn’t just Alaska’s subsistence and commercial fisheries that could be affected. Changes in habitat could affect foraging sea otters and migratory bird populations as well, among other things.
The highly invasive crustaceans have since been found further north than Metlakatla. This summer, Fish and Game discovered evidence of the crabs in eight new locations including Gravina Island, Revillagigedo Island near Ketchikan, and up into George Inlet — and Davis said they’re likely not stopping there.
“Southeast is probably not the end point for green crab expansion,” she said.
Davis, Morgan, and the Metlakatla Indian Community are part of an ad hoc statewide task force known as the European Green Crab Subcommittee. The subcommittee is housed under the Alaska Invasive Species Partnership. Davis said the partnership was founded as a platform for monitoring and early detection of all different kinds of invasive species across Alaska, as well as a place where members across the state could get on the phone monthly and discuss what their challenges and accomplishments are in the war against ecosystem invaders.
The green crab subcommittee began forming soon after those first crabs were discovered back in 2022. It loops in more than half a dozen state, federal and research groups like Alaska SeaGrant, Alaska Department of Fish and Game, NOAA, the U.S. Forest Service, and the University of Alaska Southeast.
Davis said the task force is largely fighting a war on two fronts — offering support to the places like Metlakatla where green crabs already are, and helping educate those further north on how to spot green crabs arriving in their waters.
“Never tell me the odds”
Part of the sub-committee’s goal is to talk to their partners further south, on the East and West Coasts, that have been dealing with the crabs for longer.
“I don’t think there have been any driving success stories anywhere,” said Professor Morgan. “Been a lot of effort, and really no success stories.”
One partial exception is an estuarine national park on the eastern side of Nova Scotia. Davis said the green crabs reduced eelgrass habitat around the Canadian island to roughly 2% of its normal abundance.
“They were aware of the green crab presence for 20 years,” Davis said of the Canadian park service. “And during that 20 year period — I know that seems like a long time, and we’ve only known about green crab in Alaska since 2022, even though they’ve probably been here longer — but they saw a 98% loss of native crabs in their estuary.”
The park has since managed to return its eelgrass habitat to 35% through continual trapping and restoration effort over six years. In many places that have been contending with the crabs for decades, that is the best they can hope for.
But Davis doesn’t want this to sound like doom and gloom.
“I want to be sure we are not conveying that ‘Oh, well, there’s nothing we can do about it.’ It just means that we have to keep working at it,” she said.
Reframing success
Jasmine Maurer in Homer is also on the green crab subcommittee. For her, what happened in Nova Scotia is a success story — although there’s still big questions over what exactly that means.
Maurer said Alaska has the advantage of time. Though, Alaskans on the front lines may need to reframe their definition of success.
“So, at what level can green crab be present in our environment, in our ecosystem, and [that ecosystem] still continue to function? And that might be — that’s a framework that I think is our reality,” Maurer said.
As far as the education component of their battle plan, the task force said that the goal is to teach people how to spot green crabs.
“Alaskans spend a lot of time on the water, on the beaches, and a lot of us know what looks out of the ordinary,” said Sunny Rice with Alaska SeaGrant.
The telltale sign of a green crab is five spines on either side of the eyes — they look like points at the top of the carapace — and then three little bumps in the middle between the eyes.
“And if you see something that looks out of the ordinary, take a closer look,” said Rice. “And if you see anything like that — but even if you’re just not sure — there’s lots of people, including your Department of Fish and Game office, just go show it to them, just in case.”
“Take a picture. Take 40 pictures. Send me all of them,” Davis agreed.
Knowing where the crabs are appearing, with the help of the public, will help the organizations on the subcommittee gather data, monitor movement, set traps, and target the colonizing crustaceans.
“If people are going out and collecting the carapaces and enumerating how many of each different species there are, then we have GPS data points. That gives a baseline of what we have. Then, in the future, as crabs move into that area, we can then compare what is there after they show up, and the ecological impact of them on the other crab species,” said Morgan. “What’s the impact of green crab? We don’t really know 100% right now, because we don’t have baseline data.”
Morgan pointed out, though, that it is also important not to kill suspicious crabs. There are other crabs that look similar, but are supposed to be here. The professor said she’s had trouble with people misidentifying the invaders and killing native species, which could make the problem worse.
Back in Metlakatla, Hudson, with the Indian Community, said the outlook can look grim but he’s hopeful for the future.
“In three years, ideally, we [will] have been the first organization to successfully eradicate green crab from our waters,” he said.
For more resources on identifying European green crabs, visit the Alaska Department of Fish & Game’s website.
