Invasive green crabs found in Puget Sound
ANACORTES, Wash. — An invasion has begun in Padilla Bay, with European green crabs infiltrating the mudflats and settling in among native shore crabs.
Green crabs are an invasive species that flourishes in a variety of habitats, enabling it to crowd out other wildlife.
Four green crabs have been found and removed from the area. The first was found by chance, and this week three others were lured out through a trapping effort.
Each of the green crabs was found in a different spot along about 7 miles of shoreline — from the northeast part of the bay to the southernmost trapping site.
“While I am pleased that the crabs are not more abundant, it’s somewhat concerning that they are distributed so broadly,” University of Washington research scientist P. Sean McDonald said.
Experts expect the crabs are coming from a nearby, concentrated population. This means the crabs are likely to continue making their way to Padilla Bay.
“One crab doesn’t scare me. Two crabs really isn’t that bad. What’s scary is large numbers of crabs coming in and settling broadly throughout Puget Sound,” McDonald said.
McDonald is involved with the university’s research institute, Washington Sea Grant, which coordinates European green crab monitoring with the state Department of Fish & Wildlife.
Fish & Wildlife, Washington Sea Grant and the Padilla Bay National Estuarine Research Reserve collaborated in the search this week for the crabs. The search came on the heels of the discovery of the first green crab in the bay a week earlier.
Reserve staff, volunteers trained through Washington Sea Grant’s Crab Team and others have been on the lookout for European green crabs for several years, ever since the species settled along the state’s coast and along Vancouver Island.
In some places the green crabs have impacted shellfish populations and uprooted eelgrass, which is important habitat for other crabs and fish in Padilla Bay.
“When there are a lot of (green) crabs in a confined space eating everything they can get their claws on, they can reduce the number of clams and worms and things like that in the sediment, and that reduces the food available for other species,” McDonald said.
It’s uncertain how the crabs will impact the Padilla Bay ecosystem. That will depend largely on how many there are and how well they do in the existing habitat.
“There’s concern about how it’s going to change the habitat … and the whole ecosystem,” Padilla Bay reserve research coordinator Jude Apple said.
Now that they’re here, the work is just beginning for the reserve, Washington Sea Grant and Fish & Wildlife. The organizations are discussing what to do next, including more monitoring and trapping efforts.
“It’s a really tragic but exciting opportunity for us to be at ground zero,” Apple said. “We are set up to monitor and investigate a potential invasion.”
As a national reserve, Padilla Bay is protected for research purposes, with water quality and eelgrass beds monitored closely.
Apple said the reserve will coordinate with Fish & Wildlife and Washington Sea Grant to plan increased, long-term monitoring for green crabs in the bay in order to track population changes and the impact the crabs have on the bay.
McDonald said additional trapping may be used to remove the crabs.
“Right now the population is very small. It’s just getting off the ground so anything we can do to reduce the numbers is really important,” he said. “The fewer crabs there are the less likely they are to find mates, and then they are less likely to reproduce.”
Meanwhile, the crabs found in the bay may provide more insight in the lab, where researchers can determine whether the crabs have mated and potentially reproduced.
The Padilla Bay search was arranged after reserve education coordinator Glen “Alex” Alexander found a green crab while leading a class in the mudflats on Sept. 19.
“I turned over a rock and I saw the mud moving … so I knew there was a crab there and I grabbed it and pulled it out,” Alexander said. “The first thing I noticed was that it had surprisingly long and thin legs … It was noticeably different than anything I had ever seen.”
The reserve confirmed it was a European green crab and reported the find to Fish & Wildlife and Washington Sea Grant.
The news came just as a team of researchers and wildlife managers was wrapping up a search for the green crabs in San Juan Island’s Westcott Bay, where the first confirmed green crab in the state’s inland waters was found in August.
There the surveyors found one discarded shell from a green crab.
“We were relieved to find very little evidence of a larger population of invasive European green crab in Westcott Bay,” Washington Sea Grant’s Emily Grason said in a news release. “But finding an additional crab at a site more than 30 miles away suggests that ongoing vigilance is critical across all Puget Sound shorelines.”
The surveyors set 192 traps at 31 sites in Padilla Bay this week to get a better idea of how many of the crabs are out there.
Over the next two days, three teams went to various sites where the traps were set. As they trudged through the mud to each trap, the hope was that they would find no more green crabs.
“This one looks pretty empty, which is a good thing,” said Washington Sea Grant marine ecologist Jeff Adams, as he opened one of about a dozen traps at one of the survey sites. “If we find more than one, there’s more of a chance that they are breeding, or could be.”
While only three green crabs were caught during the three-day search this week, the fact that they’re here at all is problematic.
“Having that first detection shows there are pathways bringing them in, which is a major concern because we’ve never seen that before,” said Fish & Wildlife’s Allen Pleus, who leads the agency’s aquatic invasive species unit.
Because the green crabs caught this week are roughly the same size, they are believed to be the same age, and possibly the first of their species in Padilla Bay.
“That means there is a population that is supplying these larvae, and that means we have to keep an eye out and monitor for additional crabs to be showing up,” McDonald said.
His best guess is that the green crabs were larvae from the population that is on the south side of Vancouver Island, and that they were carried into Padilla Bay by the currents.
While European green crab populations are also established in coastal areas such as Willapa Bay and Grays Harbor — and larvae can be unknowingly transported by boats or shellfish shipments — Fish & Wildlife’s Pleus said it’s more likely those in Padilla Bay came from the north.
Regardless of where they came from, it’s impossible to cordon off Padilla Bay and keep them out. McDonald said that’s why it’s important to continue watching for green crabs in the bay and removing them in an effort to limit population growth.
“It’s kind of like a ding in your windshield. One ding is not a problem, but if you don’t deal with it and it spreads it becomes a big problem,” he said.
McDonald said early detection can help prevent damage to the state’s marine habitats.
“Once volunteers or the public raise the alarm, a trapping effort can be initiated. The situations in Westcott Bay and Padilla Bay are excellent examples of how an early detection and rapid response program should operate,” he said.