Scientists, citizens track voracious predator: European green crab is not our friend

Leader Staff
Posted 7/12/16

Washington Sea Grant (WSG) is calling on beachgoers to be on the lookout for a "raving mad" crustacean that has colonized waters and threatened native shellfish from South Africa to the Pacific …

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Scientists, citizens track voracious predator: European green crab is not our friend


Washington Sea Grant (WSG) is calling on beachgoers to be on the lookout for a "raving mad" crustacean that has colonized waters and threatened native shellfish from South Africa to the Pacific Coast.

The European green crab, a small, efficient and adaptable predator also known as Carcinus maenas, meaning “raving mad crab,” was discovered in 2012 in Sooke Inlet, just west of Victoria on the south end of Vancouver Island, a discovery that sounded the alarm for Puget Sound's shellfish beds.

The green crab feeds on a variety of organisms found in estuarine environments, including native shore crabs. It has been blamed for the collapse of the soft-shell clam industry in Maine, and might likewise affect native and commercial species in Puget Sound.

In response to the threat, WSG and the state Department of Fish and Wildlife have established a citizen science program dedicated to detecting the crab and monitoring pocket estuaries so that infestations can be caught early and measures taken to reduce the crab's impacts and prevent further spread.

In addition to the monitoring being conducted in specific areas by trained "crab teams," WSG urges people to be on the lookout for the green crab while enjoying beaches this summer and to report any findings.

So far, no crabs have been found, but “that's the goal,” said MaryAnn Wagner, assistant director for communications with WSG, noting that it is an unusual goal for any project. “So far, we're meeting that goal.”


Monitoring by crab teams is in full swing after a successful pilot run in 2015. There are more than 400 potentially suitable habitat sites on Puget Sound and around the Strait of Juan de Fuca and the San Juan Islands, including several in Jefferson County.

“Jefferson County is a critical habitat, right across the water from where they were found not long ago,” said Wagner.

Visit for an interactive map with updates on findings, sites monitored and suitable habitat sites.

As shown on the map, monitoring in Jefferson County is being conducted by teams at Kala Lagoon, Discovery Bay and Zelatched Point. These three areas are pocket estuaries: lagoon-type habitats that retain saltwater at low tide, but also have some freshwater input, said Emily Grason, project coordinator. Each area has a separate monitoring group of from four to eight people dedicated to the area, said Grason.

Monitoring is also being done at the mouth of the Duckabush River; however, this location has not yet been added to the online map.

"We don't have specific plans to start monitoring at any more sites this year in Jefferson County, because we have done our major volunteer recruitment for the year already," said Grason in an email. “However, we would probably have interest in adding one or two of the medium- or high-habitat-suitability sites next year if we were able to raise enough volunteer interest to support them.”

All the habitat-suitability spots are indicated on the map. Highly suitable habitat sites in Jefferson County include: Naval Magazine Indian Island, South Indian Island County Park, Oak Bay, Skunk Island Lagoon, Mats Mats Bay, Dabob Bay, Point Whitney Shellfish Lab, Thorndyke Bay, Right Smart Cove, Toandos Peninsula State Park and southeast Toandos Peninsula.


The best way for residents to help protect Puget Sound is to learn how to recognize green crabs and report any sightings. Green crabs can thrive in a variety of coastal habitats and in wide ranges of temperature and salinity. In particular, muddy habitats such as salt marshes with deeply cut channels and sloughing banks have proven hospitable.

"I will say, however, that it is invaluable to have people keeping their eyes open on any beach or shoreline they visit, because it's entirely possible that the crabs could surprise us," said Grason in an email.

The “green” crab’s carapace color can vary widely, and several native Northwest crabs are also green. Adult green crabs are about 3 inches across at the widest part of their shell, making them smaller than adult Dungeness and rock crabs, and the shape of the green crab’s shell is triangular. The European green crab is the only crab likely to be found with five spines on the back shell from each eye to the widest point; native crabs either have more or fewer spines.

Report potential green crab sightings to the WSG green crab team by emailing Attach any photos of the crab to the email. WSG asks finders to take several pictures from different angles and distances to aid in confirming the identification. Citizens should be aware that it is illegal to possess a live green crab in the state of Washington without a special permit, so leave any green crab where you found it. Under no circumstances should you harm or kill the crab.

This project has been funded wholly or in part by the U.S. Environmental Protection Agency under assistance agreement PC 00J29801 with the Washington Department of Fish and Wildlife.

Washington Sea Grant, based at the University of Washington, provides statewide marine research, outreach and education services, helping people understand and address the challenges facing our ocean and coasts.