Tag Archives: Emily Grason

Green crabs entrenched at Dungeness Spit, but new issues are emerging

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:

  • Green crabs on Dungeness Spit
  • New findings on Whidbey Island
  • Where the crabs are NOT coming from
  • New efforts with Canada
  • First scientific paper on the green crab program
  • New assessment tool on the horizon
  • Continue reading

Invasive oyster drills react differently to predators than natives

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.

Continue reading

More invasive crabs found; wider search will resume next spring

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. The red markers show locations where invasive European green crabs were found.
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 Reserve
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.”