B5
THE ASTORIAN • SATURDAY, MAY 22, 2021
Invasive green crabs spreading along coast
By BELLAMY
PAILTHORP
KNKX
SEATTLE — European
green crabs were found in
Washington’s inland waters
in 2016, prompting exten-
sive monitoring. Now, state
offi cials say this destructive
invasive species is spreading
in several coastal locations.
They thrive in shallow
water and soft sediment,
which Washington’s estu-
aries provide. And over the
past two years, it seems the
populations of green crab
are exploding, especially on
the coast.
“Green crabs in Willapa
Bay and Grays Harbor are
appearing at densities easily
fi ve to 10 times greater than
they were ever observed
in the late 1990s. And so
that’s caught a lot of peo-
ple’s attention,” said Emily
Grason, a marine ecologist
who leads Washington Sea
Grant’s Crab Team at the
University of Washington.
She said this sudden pro-
liferation in coastal areas
is somewhat surprising
because they did not spread
rapidly after those initial
sightings two decades ago.
Now, in addition to the hot
spots on the southern end of
the coast, green crabs appear
to be spreading in Drayton
Harbor and Lummi Bay.
She said since 2016, her
team has seen the number of
detection sites and the num-
ber of green crabs trapped
each year steadily creeping
up, although not necessarily
at an even rate. Some sites
have seen declines, notably
Westcott Bay on San Juan
Island — site of the fi rst
inland trapping fi ve years
ago — and Dungeness Spit,
where only three were found
last year after fi nds of 50 to
100 in years prior. She said
it’s likely those locations do
not off er very good habitat
for green crabs.
By contrast, the coastal
locations with good estu-
ary that they have started
monitoring have recently
seen big increases. Many
of those also provide prime
University of Washington
The European green crab is considered an invasive species on the coast.
real estate for Washington’s
shellfi sh growers, whose
operations could see great
harm if green crabs continue
to proliferate.
‘Ecosystem engineers’
Green crabs are known as
voracious “ecosystem engi-
neers” that use their claws to
crush up anything that might
be edible, often dramatically
changing underwater land-
scapes and destroying eel-
grass beds and other critical
habitat for native species.
They’re not really good
to eat, but they’ve dramati-
cally reduced the harvest of
important shellfi sh species
on the East Coast, such as
soft-shell clams in Maine.
“They eat absolutely
everything. They are oppor-
tunistic predators that are
quite happy to make a living
off of anything that they can
eat,” Grason said.
Some shellfi sh growers
in Washington have seen
recent declines in some
products, such as wild-seed
manila clams, Grason said.
This has growers and sci-
entists wondering if green
crabs might be at least partly
to blame for that. She said it
will be the subject of some
of her team’s research this
year.
“There’s a lot of concern
that shellfi sh resources could
be at risk,” Grason said, both
in the coastal geographies
and inland, should green
crabs become more abun-
dant along inland shorelines
as well.
“That’s a huge part of the
economic and cultural iden-
tity of Washington state. And
so a lot of folks are working
very hard to protect those
resources from damage by
European green crab.”
She said the only way to
contain the spread of Euro-
pean green crabs is through
labor-intensive trapping and
monitoring. And they’re
likely a threat — like a virus
— that will never go away
completely.
“Nobody so far that
we’ve heard of has success-
fully eradicated European
green crab from any geog-
raphy,” Grason said. “There
are no known chemicals or
biological control agents
that would be safe and eff ec-
tive to use, so trapping is
currently the best strategy
for controlling populations.”
And she said that will be
“a really long-term project at
best.”
Taking hold
Among the places where
that reality is taking hold is
Makah Bay, south of Cape
Flattery on the Olympic
Peninsula.
Arianne Akmajian, a
marine ecologist with the
Makah Tribe, said a mem-
ber of the public found and
reported their fi rst green
crab in August 2017. A cou-
ple of months later, the tribe
started setting traps. She
said on their fi rst try, the
traps fi lled up quickly, with
34 green crabs caught in just
two days.
“So that was fairly alarm-
ing, going from essentially
not really being aware of the
species or knowing that they
were in our area to catch-
ing a pretty good number of
them just over a couple of
days,” she said.
The area around the res-
ervation has two rivers that
mix with saltwater, provid-
ing ideal habitat for the inva-
sive species, and their catch
rates have steadily gone
up. She said they have now
trapped more than 3,700
green crabs, including about
200 since the start of this
year’s trapping in April.
“What concerns me with
this season is that we are
seeing a lot of small crabs
and small molts, which to
me tells me there’s a really
good crop of crabs this year
— young-of-year crabs that
are going to grow. And so
we’re trying to do some tar-
geting of those smaller crabs
in hopes we can knock them
down a bit,” Akmajian said.
She said some are best
caught by hand and it is
labor intensive, although
they have improved their
trapping methods and are
now able to catch more
crabs with less bait.
The Washington Depart-
ment of Fish and Wildlife
has allocated some $2.2 mil-
lion to fi ghting the spread
of European green crabs.
That’s more than a third of
its $6 million aquatic inva-
sive species budget for the
2021-2023 biennium.
The state said the pub-
lic can play a key role in
helping contain green crabs
by learning what they look
like — they’re not neces-
sarily green; the best identi-
fi er is their shape, with fi ve
spines on each side of their
eyes — and snapping pho-
tos and uploading them for
state biologists to review.
They said this species is
often confused with simi-
lar-looking native crabs, so
it’s important not to handle
or try to kill any suspects.
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