Dungeness Spit on the Strait of Juan de Fuca near Sequim remains
a hot spot for the invasive European green crab, which first showed
up in Puget Sound during the fall of 2016.
This small male crab is one of
the European green crabs caught last year in traps at Dungeness
Spit.
Photo: Allen Pleus
The green crab, one of the most dreaded invasive species in the
world, brings with it the potential to destroy shellfish beds and
disrupt key habitats essential to native species in Puget
Sound.
Thankfully, except for the Dungeness Spit, new findings of green
crabs have been almost zero since a massive volunteer trapping
effort resumed in April throughout most of Puget Sound.
I do have some additional news about green crabs to share, so
please read on for a discussion of these topics:
Invasive saltwater snails, including dreaded oyster drills, seem
to be far more leery of predators than native snails under certain
conditions, according to a new study by Emily Grason, whose
research earned her a doctoral degree from the University of
Washington.
An invasive Atlantic oyster
drill feeds on a young Pacific oyster. // Photo: Emily
Grason
Why non-native snails in Puget Sound would run and hide while
native species stand their ground remains an open question, but the
difference in behavior might provide an opportunity to better
control the invasive species.
Of course, snails don’t actually run, but I was surprised to
learn that they can move quite rapidly to find hiding places when
they believe they are under attack.
Like many marine animals, snails use chemical clues to figure
out what is happening in their environment. For her experiments,
Emily created a flow-through system with two plastic shoeboxes.
Chemical clues were provided in the upstream bin, while the
reaction of the snails was observed in the downstream bin.
The most dramatic difference between native and non-native
snails seemed to be when ground-up snails were deposited in the
upstream bin, simulating a chemical release caused by a crab or
other predator breaking open snail shells and consuming the tender
morsels inside.
Padilla Bay, an extensive inlet east of Anacortes in North Puget
Sound, could become known as an early stronghold of the invasive
European Green crab, a species dreaded for the economic damage it
has brought to other regions of the country.
Trapping sites for crabs (gray
markers) during this week’s rapid assessment in Padilla Bay. Red
markers show locations where three more invasive European green
crabs were found.
Map: Washington Sea Grant
After one young green crab was found in Padilla Bay on Sept. 19
(Water
Ways, Sept. 24), three more crabs were found during an
extensive trapping effort this past week. All four crabs were
captured at different locations in the bay. These four live crabs
followed the finding of a single adult green crab in the San Juan
Islands — the first-ever finding of green crabs anywhere in Puget
Sound. (Water
Ways, Sept. 15).
With these new findings in Padilla Bay, the goal of containing
the crabs to one area has become a greater challenge. Emily Grason,
who coordinates a volunteer crab-surveillance program for
Washington Sea Grant, discusses the difficulty of putting out
enough traps to cover the entire bay. Read her report on the
fist day of trapping:
“Similar to our trip to San Juan Island, we are conducting
extensive trapping in an effort to learn more about whether there
are more green crabs in Padilla Bay. One difference, however, is
scale. Padilla Bay is massive, and it’s hard to know exactly where
to start. On San Juan Island, the muddy habitats where we thought
crabs would do well are well-defined, and relatively limited.
Padilla Bay, on the other hand, is one giant muddy habitat — well,
not all of it, but certainly a huge portion. We could trap for
weeks and still not cover all of the suitable habitat!”
In all, 192 traps were set up at 31 sites, covering about 20
miles of shoreline. The crab team was fortunate to work with the
expert staff at the Padilla Bay National Estuarine Research
Reserve, a group of folks who know the area well and had worked
with shoreline owners to get approval for access.
Three of the four green crabs caught in Padilla Bay were young,
probably washed into the bay during last winter’s warm currents,
Emily said in her wrap-up
report of the effort.
“All of the detections of European green crabs occurred on the
east portion of the bay,” she wrote. “Though the sites varied
somewhat in the type of habitat, all of the crabs were found
relatively high on the shore, in high salt marsh pools, or within a
few meters of the shore.
The first of four European
green crabs found in Padilla Bay.
Photo: Padilla Bay National Estuarine
Reserve
“Padilla Bay has about 20 miles of shoreline, and, at last count
in 2004, there were 143 acres of salt marsh habitat in the bay,”
she continued.”These numbers suggest that there are a lot of places
European green crabs could live in Padilla Bay, and protecting the
bay from this global invader will undoubtedly require a cooperative
effort.”
Yesterday, the response team held a conference call to discuss
what to do next. Team members agreed that no more intensive
trapping would take place this year, Sean McDonald of the
University of Washington told me in an email.
Winter is a tough time to catch crabs. Low tides shift from
daytime hours to nighttime hours, making trapping more difficult.
Meanwhile, crabs tend to lose their appetite during winter months,
so they are less likely to go into the traps to get food, experts
say.
Researchers, shellfish growers and beach walkers are being asked
to stay alert for the green crabs, not only in Padilla Bay but also
in nearby Samish and Fidalgo bays.
The Legislature will need to provide funding to continue the
citizen science volunteer monitoring program, which provided an
early warning that green crabs had invaded Puget Sound. Whether the
crabs will survive and in what numbers is something that demands
more study and perhaps a major eradication effort.
Meanwhile, Washington Department of Fish and Wildlife would like
to expand its overall Aquatic Invasive Species Program with
additional efforts to prevent invaders from coming into Puget
Sound. For information, check out my story on invasive species in
the Encyclopedia
of Puget Sound — specifically the section titled “Biofouling
still mostly unregulated.”
