European green crab

European green crabs are a globally damaging invasive species that pose a threat to Washington's economic, environmental, and cultural resources. Potential impacts include destruction of eelgrass beds and estuarine marsh habitats, threats to the harvest of wild shellfish and the shellfish aquaculture industry, the Dungeness crab fishery, salmon recovery, and a complex array of ecological impacts to food webs, which could negatively impact human uses and cultural resources of the Salish Sea.

In areas where green crab have been able to establish reproducing populations, they have had dramatic impacts on other species, particularly smaller shore crab, clams, and small oysters. While green crab cannot crack the shell of a mature oyster, they can prey upon young oysters, and will dig down six inches to find clams to eat. One green crab can consume 40 half-inch clams a day, as well as other crabs its own size.

Learn how a broad collaboration of volunteers, agencies, and tribes is working together to keep the crabs at bay in Washington State in this interactive story map

The video below details an ecological catastrophe in the making due to European green crabs on the Massachusetts coast. As native scallops, mussels, clams, and protective eelgrass disappear under the explosive invasion of green crabs, scientists, local experts, and residents are scrambling to save the marsh from decimation.

How to identify the European green crab

European green crab identification
Jeff Adams, Washington Sea Grant

 

 

 

 

 

 


In the Pacific Northwest, there are many small, green native crabs that are easily confused with European green crabs unless you have a trained eye. In addition, green crabs can actually turn quite red as they age. In Washington State, the European green crab is most often confused with native helmet crab or hairy shore crab.

Download the Crab Identification Guide

Spines

The most distinctive feature of the European green crab is not its color – which can vary from reddish to a dark mottled green – but the five spines or teeth on each side of the shell. This number of spines is different from any other crab you are likely to see on the beach. 

Size

At its largest, the back shell (carapace) measures up to 4 inches across, but it is more common to find smaller, younger crabs. Males are generally larger than females of the same age. 

Color

Although known by the common name of green crab, color is not its distinguishing feature. Juvenile crabs can change their shell color to match their surroundings each time they molt. Adults are usually dark greenish with yellow markings, and often have some orange at the joints. The underside of the crab is off-white, but can sometimes be bright yellow or even red. 

Shape

The back shell (carapace) is wider at the front than the back. The best way to distinguish the green crab from other species is by the number of spines next to the eye (marginal teeth). The green crab is entirely distinct from other native crabs with its five marginal teeth. 

Legs and claws

The green crab has relatively long legs compared to the main body, and narrow claws. The last pair of legs is slightly flattened. 

I think I found a European green crab - what should I do?

Report your sighting

If you find a suspected live green crab or its shell in Washington, report it as soon as possible. Take several pictures from different angles and distances to help confirm the identification. It’s also helpful to include a coin or other object to help show its size.

It is illegal to possess a live green crab in Washington, so make sure to leave the crab where you found it. This may sound counter intuitive, but this law is designed to protect native crabs from cases of mistaken identity, which is very common.

It might be hard to let a crab go when you are concerned it could be invasive, but keep in mind that WDFW will respond to any confirmed sightings quickly, and the best thing you can do is to get the information to us as soon as possible.

If you find a dead crab or an empty shell, however, you can collect and keep it to help in identification.

How to report

Phone: 1-888-WDFW-AIS (1-888-933-9247)
Online: invasivespecies.wa.gov
Email: crabteam@uw.edu
App: WA Invasives 

Are European green crabs edible?

Though edible, and fished commercially in their native range, European green crabs aren’t any bigger than your fist and don't make the most appealing meal. More importantly, the goal is to keep the populations from ever getting large enough to harvest and to prevent the ecological and economic impacts that could come with that many invasive crabs.

To protect native crab species and prevent the spread of invasive species, it is illegal to harvest European green crabs in Washington. 

Join the crab team

WDFW has teamed up with the Washington Sea Grant Crab Team who is leading a volunteer-based early detection and monitoring program for green crab. The Crab Team is also working to improve the understanding of native salt marsh and pocket estuary organisms and how they could be affected by green crabs. To learn more about early detection, monitoring, and volunteer opportunities, please visit the Sea Grant’s Crab Team website.

Limiting the invasion

The European green crab first became established in the United States in the mid-1800s, arriving by sail or steamships via transatlantic trade routes to the Cape Cod region on the east coast. In the early 1900s, green crabs spread northwards, where they are believed to have contributed to the dramatic declines in the soft-shell clam industry. In 1989, they were discovered on the West Coast, in San Francisco Bay. WDFW first confirmed green crabs in Washington waters in 1998 in Willapa Bay and Grays Harbor.

Washington Sea Grant (WSG) Crab Team

Following the 2012 discovery of a large population of green crab in Sooke Basin on Vancouver Island, WDFW established a partnership with the Washington Sea Grant (WSG) to develop a comprehensive early detection monitoring program. WSG’s Crab Team launched in 2015, engaging hundreds of community science volunteers; local, state, and federal agencies; nonprofit organizations, and 10 Salish Sea Tribes.

Shellfish transfer permits

Washington State prohibits the release of non-native species into Washington’s waters and the intentional import of live green crabs. To reduce risk of unintentional introductions, WDFW restricts movement of shellfish from green crab areas and requires that anyone seeking to move live shellfish into or around state waters be approved for an import or transfer permit, which may include precautionary treatment measures to further reduce risk.

Salish Sea Transboundary Action Plan

As the prevention of green crab infestations requires widespread help, WDFW worked with the Canadian Department of Fisheries and Oceans, the Puget Sound Partnership, and Washington Sea Grant to develop the Salish Sea Transboundary Action Plan.

Early detection monitoring

WDFW has focused much of its efforts in the early detection of green crabs by monitoring locations that offer good habitat for the species. If the species is detected at a new location, WDFW conducts rapid response actions to reduce or eliminate those new populations, and to prevent the spread of European green crab from established locations. 

Map of green crab traps in Drayton Harbor in 2020
Map of green crab trapping and captures in 2020 as of June 26. Blue dots indicate location of trap sets, while yellow dots show locations of green crab captures. Red wash indicates heat map of green crab captures. Washington Sea Grant

WSG and WDFW designed trapping protocols with the goals of removing as many European green crabs as possible, as well as simultaneously gathering robust information on green crab abundance, distribution, and population trends. Such fact finding ultimately makes removal trapping more efficient, because we can feed what we learn back into trapping strategies in an adaptive management process.

Read the 2020 Salish Sea Green Crab Update (November 2020)

Coming soon - Map of trapped European green crabs. 

Drayton Harbor

Drayton Harbor in Blaine, WA remains a regional hotspot for green crabs. So far this year, we are finding an average of about 10 crabs in every 100 trap sets, which is slightly greater than the same rate for 2019 (8.2 crabs per 100 trap sets). While 2019's assessment efforts were geographically broad, trapping efforts in 2020 has focused on sites with high capture rates and trapped them repeatedly, driving the capture rate up. 

Drayton capture rates are much higher than 2020 (to date) rates at Dungeness Spit (2 green crabs in about 1,300 trap sets), but more similar to catch rates in Makah Bay (being managed by Makah Fisheries) and Lummi Bay (managed by Lummi Natural Resources).

Read the Crab Team blog.

Washington Coast

In the last few years, shellfish growers have started finding more green crabs in their shellfish beds than they have ever encountered. In 2017, the Makah Tribe discovered a population of green crabs larger than any found along inland Washington shorelines at the mouths of the Wa’atch and Tsoo-Yess rivers. These observations have raised the alarm that Washington’s coastal estuaries could be undergoing a “sea change,” and called for renewed efforts to assess the status of green crab populations. In response to this need, WSG and WDFW are collaborating is collaborating to co-lead an assessment of invasive European green crab populations on the Pacific coast over the next year.

Read the Crab Team blog.

Presentations