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Thingy Thursday: Catch cards and a confounding crab

Few of us get a chance to see the full diversity of the Salish Sea’s crabs. Many species never venture onto the beaches. Others are small and hide well. Some even remain tucked away inside a large clam or mussel. For all the wonder, economic benefit and gastronomical pleasure crabs provide, there are several species that we don’t want to see in our waters, including the invasive European green crab, Chinese mitten crab and Asian shore crab.

European green crab (Carcinus maenas), notice the five large points on either side of the front of the carapace. Photo: Jeff Adams

Such invasive species can have dramatic economic and ecological consequences. That’s why I’m always very appreciative of folks who send notes or pictures or specimens of something unusual. Controlling the spread of marine invasive species is difficult at best, but the earlier they’re detected, the better chance we have.

I received images of a potential green crab in late August from an informed individual who had found an unusual crab at Birch Bay State Park (near Blaine and the Canadian border).

The European green crab has been present on the outer coast of Washington and up the Pacific side of Vancouver Island since the late 1990′s, but the populations have not been highly successful to date and have not found their way into the Salish Sea. Hopefully, that arrangement will continue since these buggers consume shellfish and outcompete Dungeness crab of similar size, for both food and habitat. Red rock crab on the other hand, tend to give the green crabs a serious abdomen whooping.

Green crab??? Thankfully not. Photo: Len Vandervelden

Fortunately, this is a helmet crab. It has the few large points on the front of its carapace like a green crab, and was probably a similar size (~3″ across the carapace), but helmet crabs are covered in stiff hairs and have points all the way around the back side of the carapace.

Helmet crab (Telmessus cheiragonus), a hairy or even bristly crab with several large points on either side of the front of its carapace and a couple more on the back side. Photo: Jeff Adams

The helmet crab is probably the species most commonly mistaken for a green crab. The individual in question is particularly tricky to identify since it has so many barnacles on it.

Live helmet crabs and even molts may seem unusual even to experienced beach goers. I see scores of them while snorkeling over eelgrass that’s exposed at low tide, but I rarely see them alive on the beach when the tide is out. I guess it’s no surprise that as one of the fastest Pacific Northwest crabs, a helmet crab would rather retreat with the tide than try its luck hiding from gulls in the eelgrass and algae.

Back to the European green crab… Fortunately, it isn’t living up to the initial concern in our state, but there are a lot of unknowns if it gets into the Salish Sea or if conditions change in our waters. It’s certainly important to keep a watchful eye.

Always feel free to send observations, pictures or thoughts of things extraordinary or out of the ordinary. If I can’t share part of its story, I enjoy looking for someone who can and learning together.

Oh, and just a reminder for all you crabbers… Whether you caught Dungeness or not, don’t forget to put your Puget Sound crab catch cards in the mail or enter the data online by October 1 to avoid a $10 penalty and to help managers determine how much crab should be harvested in the winter season. Happy autumn!

Jeff Adams is a Washington Sea Grant Marine Water Quality Specialist, affiliated with the University of Washington’s College of the Environment, and based in Bremerton. You can follow his Sea Life blog, SalishSeaLife tweets and videos, email to jaws@uw.edu or call at 360-337-4619.