Invasive crab species detected in Drayton Harbor

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An invasive crab species has been detected in Drayton Harbor, worrying experts who are concerned about the potential impact to marine ecosystems in the region.

In August, Margarette Grant and Margaret Santamaria found the shell of an invasive European green crab while walking along the beach in east Drayton Harbor, between Dakota Creek and California Creek. They were conducting a survey for a citizen science project, the Coastal Observation and Seabird Survey Team (COASST), when they discovered the shell of a 50-millimeter male European green crab mixed into the seaweed wrack that had washed up on the beach.

“It was like ‘uh-oh’ – that pit in your stomach,” said Grant.

The European green crab is a small shore crab whose native distribution is in the northeast Atlantic Ocean and Baltic Sea, ranging along coasts from northern Africa to Norway and Iceland. The recent arrival of the green crab on America’s west coast has alarmed experts, because the species has the potential to significantly alter any ecosystem it invades.

The green crab could threaten Dungeness crab, oyster and clam fisheries in the Pacific Northwest. This is because the green crab feeds on many organisms, including clams, oysters, mussels, marine worms and small crustaceans. It can also prey on native juvenile crabs and shellfish.

“It will eat anything that it can get its claws around,” said Emily Grason, a marine ecologist with Washington Sea Grant at the University of Washington. “It could be other species of native crab, and it could also be things like eelgrass beds. There’s research that the green crabs will dig them up, damaging the habitat for juvenile salmon.”

According to Grason, there have been six detections of European green crab in Whatcom County this year. Three live crab were found in a trap in Chuckanut Bay in July, and the remains of one were found in Squalicum Harbor in Bellingham in May. There was the August discovery of a shell in east Drayton Harbor by Grant and Santamaria, and more recently, on September 1, Grant spotted another shell when she was walking along the beach to the west of the Dakota Creek Kayak Trail.

Grant is a member of Washington Sea Grant’s Crab Team, a network of volunteers who use citizen science to achieve a much greater scale of monitoring than would otherwise be possible. She immediately sent photos of her most recent discovery to Grason, who determined that it was the shell of a green crab that had recently molted (shed its shell) in the process of growing.

The next step is for Grason to physically inspect the shell, after it is dropped off in Seattle by Grant or Santamaria. “If we can confirm it’s a European green crab, the goal is to look around and get as much information as to where the crab might have come from,” said Grason.

Despite the name, European green crabs are not necessarily green. They can be all kinds of colors including orange, red and brown, depending on the age of their shell. The juveniles can even have shells with white and black patterns. Meanwhile, native crab species can be greenish in color, leading to further confusion. “The color isn’t a reliable feature to figure out what you’re looking at,” said Grason.

The best way to determine if a crab is a European green crab is to look at the outside of each eye on the back shell. European green crab will have five teeth, or spines, next to each eye. This sets the European green crab apart from other species.

It is unlikely that people going crabbing will catch European green crabs, because a lot of crabbing gear won’t collect green crabs and living green crabs don’t tend to overlap with legal-size Dungeness and rock crabs. But if someone thinks they have a green crab, or sees one while walking on the beach, they can take a photograph and email it to Washington Sea Grant’s Crab Team at crabteam@uw.edu. The team prefers to receive multiple photos from different angles, with another object in the photo for scale.

If the crab is identified as a green crab, Washington Sea Grant will work with the Washington Department of Fish and Wildlife (WDFW) to set traps in the area.

Later this month, scientific technicians with WDFW plan on conducting a “rapid response” to the recent discoveries of European green crab molts in Drayton Harbor. In a rapid response, WDFW scientists quickly set traps in any suitable habitat in the surrounding area.

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