It’s almost like something out of a horror movie. Waves of invasive European green crabs are threatening the Coos Bay estuary, and its existing population of Dungeness crabs, as well as clams, oysters, and mussels, according to a recent report published by South Slough National Estuarine Research Reserve.
The report comes on the heels of a 19-year study conducted by the Reserve and Oregon State University scientists, during which researchers trapped crabs annually throughout the Coos Bay estuary, on Oregon’s southern coast. In 2020, about 77% of the crabs caught were European green crabs. The green crabs were found at all sites, but were most abundant in mid to upper parts of the estuary, the study found.
The number of green crabs collected in the estuary has consistently increased since 2016, when the average number of crabs caught in each trap set by the researchers was less than one (0.92). In 2020, an average of 4.66 green crabs were caught per trap.
Green crabs are an invasive species that established in the San Francisco estuary before 1989 and have since moved north to Southern Oregon. The researchers said that 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.
Green crabs have been linked to declines in eelgrass, which is an essential habitat and food source for marine and estuarine organisms, as well as a valuable component of marine ecosystems that helps to keep the water clean and protect shorelines from storms.
Green crabs may also reduce Dungeness crab populations by eating juvenile crabs and by displacing young Dungeness crabs from sheltered habitats, making them vulnerable to predators. Additionally, green crabs consume clams, oysters, and mussels and may reduce their populations.
Reserve researchers plan to continue monitoring green crab populations in Coos Bay. More research is needed to understand the effects of the growth of the green crab population on habitats and food webs, as well as inform options for managing green crab populations, the researchers said.
Crabbers who believe they have caught a European green crab should follow guidance from the Oregon Department of Fish and Wildlife website, at https://www.dfw.state.or.us/, to identify the green crab, which is often mistaken for other crab species. All green crabs that are caught can be brought to the nearest Department of Fish and Wildlife office.