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.
Share on Facebook
Scripps Interactive Newspapers Group
Recent Comments