Invasive crabs detected for first time on Orcas Island

An invasive European green crab was found on Orcas Island for the first time.

European green crabs are a species of small shore crab known for damaging ecosystems, including in North America.

They eat eelgrass, algae, baby clams, oysters and young native crabs, and when they dig up eelgrass, it destabilizes soil.

Although the species was first identified in the state in 1998, its population began to soar in 2021.

According to a Thursday news release from Washington Sea Grant, 24 students from an Orcas Island Middle School marine science exploratory class went in May to the island's Crescent Beach for a mock search for the crab species.

In a surprise, seventh-grade student Paxton Erwin found a molt with the species' distinctive five ridges.

A molt is the hard outer shell that is shedded as a crab grows.

"I was thinking it was a bummer to find it because they're bad for our environment but also kinda good that we know they're here," Erwin said in the news release.

Orcas Island Middle School science teacher and Washington Sea Grant volunteer Amy Sprenger reported the molt to the Washington Sea Grant's crab program.

"It was great exposure to real science for my students," Sprenger said in the news release. "They know they can meaningfully participate in the effort to understand and protect our local marine ecosystem. Students were regularly asking for updates on the WDFW trapping efforts around our island and will be interested to hear about where green crabs were and were not found around Orcas."

As a follow-up effort, the state Department of Fish and Wildlife began trapping efforts on the island.

A large green crab was trapped at Deer Harbor on the west side of the island, and had likely been at the site for at least three years. It was determined to be a different crab than the one that had shed the shell found by the middle schooler.

The last detection of European green crabs in San Juan County were small numbers on San Juan Island - the only detections within the county.

According to Washington Sea Grant, the new green crabs have likely arrived at Orcas from separate dispersals.

On June 26, the Sea Grant's crab program will hold a Salish Sea Molt Blitz, a one-day event intended to search throughout much of the Salish Sea for green crab molts.

"The local enthusiasm for protecting shorelines from green crab is critically important, given how much coast there is to cover in the county," the Washington Sea Grant wrote in the news release.

"As green crabs continue to spread within the Salish Sea, searches for molts are yielding new detection locations that can point managers to previously undiscovered populations."

The blitz event includes six sites in the San Juan Islands, including one on Orcas.

Those interested can sign up online at wsgcrabteam.uw.edu

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