European green crabs feast on shellfish, destroy marsh habitats by burrowing in the mud and obliterate valuable seagrass beds. The invasive species also reproduces quickly, making it a nightmare for wildlife managers seeking to control its spread in Washington’s marine waters.

Last month, Gov. Jay Inslee issued an emergency order in response to more than 70,000 crabs caught on Lummi Nation land as well as dramatic increases in crab populations on Washington’s outer coast and other locations in Puget Sound in recent years.

As the green crab invasion in the state worsens, a new analysis method developed by University of Washington and Washington Sea Grant scientists could help contain future invasions and prevent new outbreaks using water testing and genetic analysis. The results, published online Feb. 6 in the journal Ecological Applications, show that the DNA-based technique works as well in detecting the presence of green crabs as setting traps to catch the live animals, which is a more laborious process. Results suggest these two methods could complement each other as approaches to learn where the species’ range is expanding.

“We have limited resources to be able to combat this problem, and it’s important to think about how to allocate those resources efficiently and effectively,” said lead author Abigail Keller, who completed the work as a master’s student in the UW School of Marine and Environmental Affairs. “Knowing the best situations for using eDNA to detect invasive green crabs is important, and that’s what our study tried to tackle.”

The research team relied on data collected over three months in 2020 from green crab traps in 20 locations throughout Puget Sound and the outer coast. Trapping at these locations was done by a large number of partners participating in statewide efforts to monitor and control European green crab, including multiple tribes, Washington Department of Fish and Wildlife — the state lead for green crab management — Washington Sea Grant’s Crab Team, and other state and federal agencies.