Wicked little arthropod found on San Juan Island

A member of an invasive crab species that indirectly threatens our delicious Dungeness variety and preys on clams and oysters was found at Westcott Bay on San Juan Island last week.

Volunteer monitors caught a European green crab, which doesn’t belong in our waters, but seems determined to homestead here anyway.

A team of volunteers from Washington Sea Grant caught the three-inch adult male as part of the Crab Team’s regular monitoring program.

European green crabs are native to the eastern Atlantic and Baltic Sea, but they have migrated as stowaways on ships. The creature was first seen in American waters about 200 years ago.

Since then it has colonized the northeastern seaboard and the Pacific Northwest coast. The Washington Department of Fish & Wildlife is working with Sea Grant to keep it from becoming common in interior estuaries and eelgrass forests favored by our native sea life.

The green crab, also known as the European shore crab, is only about half the size of the “keeper” Dungeness crabs fishers haul in around here, but it has nasty habits.

It is an omnivore and essentially eats everything. Sea Grant Marine Ecologist Jeff Adams said it has also been implicated in digging up eelgrass forests on the east coast — something that could hurt lots of native species, should they do it here.

While our Dungeness or red rocks would likely kick butt in combat with the smaller green crab, the invasive species has parasites in its native range that could be very harmful if they ever show up here, Adams said.

The crab found at Westcott Bay has been checked for parasites and was clean, he said. It is now in a freezer at a lab in Friday Harbor.

Adams said the volunteer monitors and scientists have been looking for the green crab in the Strait of Juan De Fuca and Salish Sea since 2012, always hoping never to find one. The one found last week likely floated in as a larva on currents, he said, possibly from the outside waters of Vancouver Island, where they have established colonies.

The Sea Grant Crab Team is asking the public to keep a lookout for the invasive species. The easiest way to identify them is by their carapace, which has five spiny points on each side between the eyes and front legs, and three bumps between the eyes.

While they often come in shades of green, they can be brown or even kind of red depending on what stage of their molting process they’re in.

Adams said green crabs are not likely to turn up in recreational crab pots because they like protected estuaries and muddy areas. People are more likely to encounter them from the shore.

Since they’re a prohibited species in Washington, it’s against the law to take them. State Department of Fish and Game spokesman Jason Wettstein said in theory at least, someone could be cited for catching and keeping a green crab. So the best thing to do is just photograph them, release them and report them as fugitives so the Sea Grant Crab Team can hunt them down and capture them.

The important thing, Wettstein said, is for people who encounter these creatures to report the location. That way the crab team can “take a really solid look at the area when they try to identify hot spots.”

One crab by itself is not going to destroy the ecosystem; but where there’s one, there cold be a whole colony.

Anyone who finds a green crab or its molted carapace, is asked to contact the crab team at [email protected], describe where it was found and send a photo if possible.