Tag Archives: Carcinus maenas

A single green crab invader has been found, the first in Puget Sound

A European green crab, one of the most dreaded invasive species in the world, has finally arrived in Puget Sound.

Caught in a crab trap on San Juan Island were these animals — including the first European green crab ever found in Puget Sound. Photo: Photo Craig Staude, courtesy of Washington Sea Grant
Caught in a crab trap on San Juan Island were these fish, along with the first European green crab ever found in Puget Sound.
Photo: Craig Staude, courtesy of Washington Sea Grant

A single adult green crab was caught in a trap deployed on San Juan Island by a team of volunteers involved in a regionwide effort to locate the invasive crabs before they become an established population.

Until now, green crabs have never been found in Puget Sound, although they have managed to establish breeding populations along the West Coast — including Willapa Bay and Grays Harbor in Washington and the western side of Vancouver Island in British Columbia.

Coincidentally, I recently completed a writing project on invasive species for the Encyclopedia of Puget Sound, including a story about green crabs and the volunteer monitoring program.

Here’s what I wrote: “Puget Sound has so far avoided an invasion of European green crabs — at least none have been found — but the threat could be just around the corner….

“Green crabs are but one of the invasive species threatening Washington state, but they are getting special attention because of fears they could seriously affect the economy and ecosystem of Puget Sound. Besides devouring young native crabs and shellfish, they compete for food with a variety of species, including fish and birds.”

Along the beach, careful observers can often find crab molts. The green crab, upper left, can be distinguished by the points on its carapace. Photo: Jeff Adams, Washington Sea Grant
Along the beach, careful observers may find weathered crab molts of all sizes. The green crab, upper left, can be distinguished by the five points on each side of the carapace. (Click to enlarge.)
Photo: Jeff Adams, Washington Sea Grant

In Canada, one breeding population has been identified in Sooke Inlet near the southernmost tip of Vancouver Island. That’s about 40 miles away from Westcott Bay, where Puget Sound’s first green crab was found on Tuesday.

It is likely that the crab traveled to San Juan Island in its early free-swimming larval form by drifting with the currents, said Jeff Adams, a marine ecologist for Washington Sea Grant who manages the Crab Team of volunteers. This crab likely settled down in suitable habitat and located enough food to grow into an adult. Based on the crab’s size, it probably arrived last year, Jeff told me.

European green crab Photo: Gregory C. Jensen, UW
European green crab // Photo: Gregory Jensen, UW

Finding a green crab in Puget Sound is alarming, Jeff said, but it is a good sign that the first crab was found by the volunteer monitors. That suggests that the trapping program is working. If this first crab turns out to be a single individual without a mate, then the threat would die out, at least for now.

The concern is that if one crab can survive in Puget Sound, then others may also be lurking around, increasing the chance of male-female pairing. The next step is to conduct a more extensive trapping effort in the area where the first green crab was found, then branch out to other suitable habitats in the San Juan Islands, Jeff said. The expanded effort is planned for the week of Sept. 11 and will include a search for molts — the shells left behind when crabs outgrow their exoskeletons and enter a new stage of growth.

Green crab
Green crab

Researchers and others who work with invasive species quickly recovered from their initial surprise at finding a green crab in Puget Sound, then got down to business in planning how to survey for crabs and manage their potential impacts.

Allen Pleus, coordinator of the Aquatic Invasive Species Program at the Washington Department of Fish and Wildlife, told me several weeks ago that if green crabs show up in Puget Sound, one idea would be to conduct an extensive trapping program to eradicate or at least reduce their population. First, however, the extent of the infestation must be identified. I expect that more extensive trapping will be planned next spring and summer to look for offspring from any successful mating in the San Juan Islands.

This video shows a green crab found in Willapa Bay on the Washington Coast.

Typically, green crabs are found in marshy areas, which are habitats extensively used by our native hairy shore crab. But Jeff tells me that some populations of green crabs seem to be expanding their habitat into more exposed rocky areas.

With roughly 400 suitable sites for the crabs in Puget Sound, invasive species experts are calling for everyone who visits a beach to look for green crabs and their molts. One can learn to identify green crabs from the Washington Sea Grant website. The volunteer trapping program is funded by the Environmental Protection Agency with a grant to Fish and Wildlife.

A public discussion about green crabs and how people can help protect Puget Sound from an invasion is scheduled for Sept. 13 at Friday Harbor Laboratories on San Juan Island. See Crab Team Public Presentation.