Howe Sound is home for an abundance of marine creatures, including many different species of crabs. It’s also currently under threat of a European Green Crab invasion – this aggressive invasive crab competes for prey and has the potential to upset the overall balance of our local marine ecosystem. European Green Crabs feed on a variety of intertidal animals, including oysters, mussels, clams, small fish, and juvenile crabs. They’ve also been known to disrupt eelgrass beds (important habitat for young salmon) and can destroy shellfish habitat.
To-date, there have been no detections of European Green Crab in Howe Sound, but they have been found as close as Salt Spring Island, San Juan Island (in the US), Boundary Bay (just south of Vancouver), along the Sunshine Coast, and all over the West Coast of Vancouver Island.
We need your help to keep an eye out for European Green Crabs, as early detection and rapid response (EDRR) are extremely important in fighting the threat of invasive species. We launched our monitoring program last year, but can only feasibly sample at a few sites around the sound.
So how do you tell the difference between a native crab and an invasive European Green Crab? We’ve put together this guide with some helpful tips.
If you do think you’ve spotted one, please report it immediately to Fisheries and Oceans Canada.
Habitat
European Green Crabs can tolerate a wide range of water temperatures and salinities. Populations often first establish in salt marshes, muddy estuaries, sandy beaches, or rocky bays. This crab prefers sheltered areas, such as in undercut mud banks.
We’re concerned that the sensitive Squamish Estuary ecosystem would be preferred habitat for European Green Crabs. If you’re out walking along it’s shores, paddling through the brackish channels, or windsurfing off the Spit, keep a look out for crabs in the muddy, vegetated banks.
Though they prefer these sheltered locations, of course it’s also possible that these invasive crabs could survive elsewhere in Howe Sound. Marinas and boat launches are another possible area that you may spot one – the crabs can easily hitch a ride on fishing gear or other equipment, and then get deposited in a new location.
In comparison, many of our native crabs will often be found in deeper, less brackish waters. Though we have caught juvenile Dungeness crabs in areas like the Mamquam Blind Channel, so make sure to use the next tips to confirm the crab species.
Shape
Counting the number of spines on a crab’s shell is one of the best ways to confirm or deny that you’re looking at a European Green Crab. They have 5 spines on either side of their eyes, and 3 in between. Their shell is also distinctly pentagon-shaped.
There are no native crabs that have 5 spines. The most similar looking crabs in terms of number of spines and shell shape are shore crabs (multiple species). These little guys have 3 spines, and their shells are more square-shaped.
Colour
Despite the name, European Green Crabs are not always green. Confusing, we know!
Though a mottled dark green is common, their shells can be a variety of other colours, including dark brown, orange, red, and yellow.
Native crabs also come in a variety of colours of course, depending on the species and age of the crab. Many native crabs can be green, so don’t rely on looking for a “green” European Green Crab.
Behaviour
European Green Crabs are known to be quite feisty. They are aggressive and territorial, so if you observe one or try to pick it up, make sure to watch out for it’s claws! The best way to pick up a crab is from behind – with your thumb on the top shell, and one or two fingers on the bottom shell.
Native crab behaviour varies depending on the species. Some native crabs are also quite aggressive, such as Dungeness, meanwhile others are more docile, such as Graceful or shore crabs.
Size
European Green Crabs pack a big punch relative to their size. They only grow up to about 10cm wide (across their shell, not including legs). This is why we use traps with small openings when we’re monitoring for European Green Crabs.
In comparison, many of our native crabs, including Dungeness and Red Rock, grow larger than 10cm wide. Some grow much smaller though, such as shore crabs (various species). So if you see a small crab, make sure to take a closer look for the number of spines on their shell.
Crabs of Howe Sound
Still curious about crustaceans? Check out our Crabs of Howe Sound ID Guide for some more information about crabs that you may come across in our local marine ecosystems.
- European Green Crab (INVASIVE)
- Dungeness Crab (NATIVE)
- Shore Crabs (NATIVE)
- Graceful Crab (NATIVE)
- Red Rock Crab (NATIVE)
- Northern Kelp Crab (NATIVE)
You can learn more about crabs (and other neat marine creatures) in books such as “Whelks to Whales“, on Fisheries and Oceans Canada’s website, or through this informative video from Washington Sea Grant.
Reporting
If you think you’ve spotted a European Green Crab, please:
- Take a picture
- Note down your location (GPS coordinates)
- Send an email with info / photos to Fisheries and Oceans Canada
- Email: AISPACIFIC@dfo-mpo.gc.ca
- Phone: 1-888-356-7525
More Resources
Have we ‘pinched’ your interest? Here’s some useful links:
- Learn more about Crab Team and our monitoring efforts
- European Green Crab species profile page from Fisheries and Oceans Canada
- European Green Crab species profile page from Sea to Sky Invasives Species Council
- Impacts of European green crab in British Columbia webinar via ISCBC
- The Squamish Community Foundation’s blog post about SSISC’s EGC program
Add Comment