Preventing a green crab invasion
A hungry invader that poses a threat to the region’s marine life has been found in Whatcom County, most recently in Drayton Harbor where the shell of a European green crab was discovered in August.
It’s not the first time one has been found within Whatcom, but scientists, tribes and volunteers are working to keep the non-native pests from making a home here and elsewhere in the state’s saltwater shorelines.
Three live crabs were found in a trap in Chuckanut Bay in July, and the remains of one were found in Squalicum Harbor in Bellingham in May, marking the first confirmation of the invasive species’ presence in Whatcom County, according to Washington Sea Grant at the University of Washington.
Five? That’s not so many.
“How much damage can they do?” acknowledged Emily Grason, a marine ecologist and the Crab Team Program manager for Washington Sea Grant, of a common question.
But it’s what may be lurking that’s of concern.
“That means there are more out there,” Grason said to The Bellingham Herald.
And if the non-native European green crabs are left alone to reproduce until they become established here, they will become a big problem.
Considered one of the world’s worst invasive species, Carcinus maenas are voracious eaters and skilled predators that could prey on native shore crab species, compete with native fish for food and hurt the shellfish industry here, according to Washington Sea Grant.
“They will directly compete with and prey on any crab that’s smaller than they are,” Grason said.
And that could include native Dungeness crabs, which are smaller when they’re younger. There’s a commercial fishery for Dungeness in the state.
European green crabs like a variety of coastal habitats and can thrive in wide ranges of temperature and salinity, especially muddy habitats such as salt marshes with deeply cut channels and sloughing banks, according to Washington Sea Grant.
They are native to the shores of the Baltic Sea and the northeastern Atlantic Ocean, ranging from northern Africa to Norway and Iceland. They’ve been a problem on the East Coast, where they are multiplying and have been blamed for the collapse of the soft-shell clam industry in parts of Maine.
European green crabs were first found on the West Coast, in San Francisco Bay, in 1989, then spread south to Monterey Bay and north to Humboldt Bay in California as well as Coos Bay in Oregon.
They were discovered in Washington state waters in 1998, in Willapa Bay and Grays Harbor.
Monitoring in the state has occurred since the late 1990s. Their numbers seemed to dwindle after they were first introduced to Washington, but monitoring intensified in 2016 after they were found for the first time in Washington’s inland waters, in Westcott Bay on San Juan Island.
Crab monitoring season runs April to September.
More recently, Dungeness Spit and Neah Bay on the Olympic Peninsula have been hot spots where hundreds of European green crabs have been found.
Get them early
The best way to keep their numbers from growing is to trap them and to do so early. That’s not easy, given the more than 2,500 miles of shoreline in the state where the crabs could survive — something Grason described as being akin to looking for a needle in a haystack.
What’s more, trapping means carrying a lot of gear into muddy environments by foot.
But European green crabs are edible, so why not just eat them?
They’re on the small side, for one, according to Grason.
Then there’s the damage they could do to the marine ecosystem if the population takes hold in the state.
“This particular crab has the potential impact to displace Dungeness crab,” Grason said. “We could be losing lots of other things in the process.”
That loss could include vitally important eelgrass.
Eelgrass meadows provide critical habitat for species, including juvenile salmon and herring as well as molting Dungeness crab, so they’re protected by the state of Washington. They’re also important foraging habitat for migratory shorebirds.
There’s been some evidence, particularly in Canada, that European green crabs damage eelgrass beds by ripping through them as they forage for food, according to Grason.
“If eelgrass is at risk,” Grason said, “then a lot is at risk.”
How to help
▪ Learn how to identify European green crabs. Then keep your eyes open for them during your beach walks.
▪ Think you see one? Take a photo but leave the crab where it is.
▪ Report possible European green crab sightings by emailing email@example.com. Attach photos, taken from different angles and distances, of the crab to the email. Include the location. You will be contacted if more information is needed.
Green crab ID
Identifying the European green crab can be challenging, partly because the color of its top shell can vary widely. Plus, several native Northwest crabs are green, too.
▪ Adult green crabs are about 3 inches across at the widest part of their back shell, making them smaller than adult, native Dungeness and rock crabs.
▪ It’s the only crab likely to have five spines (or teeth) present from each eye to the widest point along the front edge of the back shell.
▪ Juveniles can change color to match their surroundings each time they molt. Adults are usually dark-greenish with yellow markings, and often have some orange at the joints. The underside of the crab is off-white, but can often be bright yellow or even red.