When a young Sealaska intern walking a beach in July 2022 found the first evidence of European green crab presence in Alaska – a discarded shell on a beach on Annette Island in the state’s far southeast corner – it was an ominous sign about the invasive species’ northward spread.
Since then, the Metlakatla Indian Community, the tribe based on Annette Island, and its partners, which include Alaska Sea Grant, have found not just more shells, but live invasive crabs. Discoveries numbered just a handful at first, then dozens, then hundreds, then thousands.
This year, the Metlakatla tribe’s team has trapped more than 40,000 of them on and around Annette Island, a representative said.
“This year we’ve had a complete explosion of green crab — over seven new locations on Annette Island we found green crab, and eight new locations off Annette Island,” said Nicole Reynolds, an environmental specialist working with the tribe, in a presentation at a three-day Anchorage meeting on invasive species in Alaska this week.
The more than 40,000 crabs removed this year compares to last year’s total of 1,800, Reynolds said.
European green crabs are small, usually measuring no more than 4 inches wide, but they are powerful forces of destruction. They mow down eelgrass beds that are vital habitat for salmon and other native species. And they gobble up native marine life like juvenile salmon, clams, mussels and juvenile Dungeness and other crabs that are important to commercial and subsistence harvests.
“They’ll eat the baby crabs. They’re meaner and tougher than the Dungeness,” Reynolds said during a break in the annual Alaska Invasive Species Partnership Workshop.
European green crabs have already spread north of Annette Island. Last year, they were found at Gravina Island, and this summer they were found by participants in a local university class at beaches in Ketchikanthat lie about 30 miles north of the initial Annette Island discovery site.
Just this month, they were found at Etolin Island, Reynolds said. Etolin Island is roughly 60 miles northwest of the city of Ketchikan, making it the northernmost North America discovery to date.
And now European green crabs appear to be entrenched in Alaska waters for good, Reynolds and Genelle Winter, a grant administrator with the tribal government, told the workshop audience.
That means the fight against green crabs will also have to be long-term, Winter said, with a permanent staff and a strategy of what is known as “functional eradication.” That is an eradication strategy that accepts the reality of the invaders’ presence in some places, but tries to keep them out of other places with resources that are most important to protect.
Such a strategy involves “focusing all our efforts on protecting the most vital subsistence and commercial resources,” she said.
Conditions in Alaska waters, the farthest-north spots in North America where the crabs have spread, do not faze the invaders, DNA analysis shows. For that information, the tribe consulted with an expert, Carolyn Tepolt of the Woods Hole Oceanographic Institute. Tepolt has also been investigating the genetics of green crabs that have invaded Washington state.
Tepolt’s analysis found that the green crabs in Alaska are a genetic blend of those in Washington and British Columbia, diverse enough to persist in the more northern waters, Reynolds said.
“She even called it a ‘super-crab’ just because of how perfectly genetically suited it is for the environment in Southeast Alaska,” Reynolds said.
European green crabs have been altering North American marine ecosystems for a long time.
They were first found in East Coast waters in the early 1800s, likely carried there in ship ballast water. The first West Coast discovery was in 1989 in San Francisco Bay. Since then, they have been spreading north up the Pacific coast. They were first confirmed in British Columbia in 1999 and continued moving up that Canadian province’s coast before being found at Annette Island three years ago.
Beyond the accidental releases through ballast water, scientists say warming conditions are aiding the spread of green crabs. Larvae are more likely to survive in warmer waters brought on by climate changeand weather events like El Nino cycles.
The 2023-2024 El Nino, which warmed Alaska waters, is a possible factor in this year’s explosion of green crabs in Southeast Alaska, the Metlakatla tribal representatives said.
Warmer temperatures than those that used to be normal in Alaska marine waters are known to encourage green crab proliferation.
A study by Danish scienetists that was published in September identifies a temperature range that appears ideal for the crabs. At temperatures of 12.5 to 16.6 degrees Celsius, or 54.5 to 61.9 degrees Fahrenheit, European green crab abundance peaked, the scientists found.
Average temperatures in Southcentral Alaska’s Cook Inlet were within that range this August, an indication that conditions would be suitable for green crabs if they somehow reach that area.
Preparations are already underway in Alaska for what experts believe is an inevitable spread north from the Southeast region.
In Southcentral Alaska’s Kachemak Bay, over 700 miles northwest of Ketchikan, residents this summer deployed over 60 traps in what was effectively a pre-invasion drill. The program was a cooperative effort of the Kachemak Bay National Estuarine Research Reserve, the Seldovia Village Tribe and its council member, Michael Opheim, and the U.S. Fish and Wildlife Service.
There and elsewhere, a big part of the fight against green crab infestations is public education.
European green crabs can be identified by the array of bumps on their shells. They have five sharp spikes on either side of their eyes and three lobes in between their eyes. Despite their name, they are not always green – they can be red, yellow or mottled. Some of those found by her team have even been blue, Reynolds said.
To help boost awareness, local Tsimshian artist Elizabeth Anderson has designed a green crab logo – with an angry face to reinforce the message that the species is a bad actor, Winter said.
In Metlakatla, awareness appears to be keen already, including among some of the youngest residents.
“The other day, the mayor was driving down the street and got flagged down by two little kids. And they said, ‘We found some green crab! We know its green crab because it’s 5-3-5,’” Winter said during the workshop presentation. The numbers reference the array of shell bumps on a green crab. “Those little kids absolutely knew how to identify the European green crab.”
Those crabs, found at a beach right in front of town, were stashed in a plastic bag and added to this year’s count, Winter said.
Aside from identifying, trapping, counting, measuring and analyzing the European green crabs, the inundated community faces another challenge: what to do with thousands of unwanted invaders.
In Metlakatla, the ultimate destination is the community compost heap. That is a good end use, Reynolds said. “They add heat to the compost, and because it’s cold and wet in Southeast, it’s actually really helpful to have more heat,” she told workshop attendees.
On the East Coast and elsewhere, some of the eradication work involves eating the invaders. Experts say they have little meat but can be useful for making soups. One organization, Greencrab.org, has compiled recipes and sells a cookbook and T-shirts with a catchy slogan: “If you can’t beat them, eat them.”