Growing European green crab populations throughout Coos Bay are likely to impact Dungeness crabs and coastal habitat, according to a new report by researchers at South Slough National Estuarine Research Reserve.

The report — part of a 20-year study by scientists at South Slough Reserve and Oregon State University — found that numbers of invasive green crabs continue to climb. Between June and September 2021, researchers trapped and sampled crab populations daily at 13 sites around Coos Bay. On average, 73.3% of crab species trapped each day were green crabs. In 2020, about 77% of the crabs caught were green crabs.

“Green crab numbers have reached a critical point where we can begin to expect negative impacts on surrounding coastal and estuarine habitat and other organisms,” said Dr. Shon Schooler, lead scientist and research coordinator at South Slough Reserve. “This, in turn, may impact our local fisheries.”

Green crabs dig up and eat eelgrass meadows, destroying the seagrass many organisms rely on for food and shelter. They also displace juvenile Dungeness crabs from habitat where they shelter and feed, leaving Dungeness vulnerable to predators. Additionally, green crabs prey on clams, oysters, and mussels, reducing the populations of these bivalves.

Dr. Sylvia Yamada, an assistant professor at Oregon State University, said the rise in green crabs measured in Coos Bay reflects what is happening in other estuaries along the Oregon Coast.

“All estuaries follow similar trends,” Yamada said. “In the past, green crab larvae were carried in warm ocean currents to Oregon from established populations in California. Now that green crabs are abundant in Oregon, Washington and British Columbia, there is evidence some larvae are coming from the north, while others are reproducing locally. This doesn’t bode well for the future unless we get a series of years when the water is colder.”

Green crabs are an invasive species that established in the San Francisco estuary before 1989 and have since moved north to Southern Oregon. Researchers say the green crabs likely thrive in Coos Bay because of available food and shelter.

The increase in green crabs could harm coastal species and habitats, the researchers said. But there is one way to help curb the crab problem — catch and eat them.

Coastal residents and visitors can help reduce the environmental impacts of green crabs by catching and removing this invasive species from coastal waters. In addition to the report, researchers released a culinary guide with information about preparing and cooking green crabs, including compiled recipes for green crab soup stock, risotto, and more.

Green crabs may vary in color from green to yellow or orange. They have five spines on each side of their shells and three bumps between their eyes. Always check for these identifying marks before removing possible green crabs. Green crabs can be brought to the nearest Oregon Department of Fish and Wildlife office, or taken home and eaten.

Scott Carroll can be reached at scarroll@nrtoday.com or 541-957-4204. Or follow him on Twitter @scottcarroll15.

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