Green Crabs in Seadrift

The impact of Green Crabs on the Ecosystem.

The impacts of high densities of green crabs are especially evident in Seadrift Lagoon. They have all but driven out the native crab species from the lagoon leaving few native crabs, other large invertebrates, or fish. Seadrift Lagoon presently hosts the highest density of green crabs along the US west coast, and catches have exceeded all the other sites we have sampled recently. The large population of green crabs in Seadrift Lagoon may be acting as a source of dispersing larvae to the rest of Bolinas Lagoon as well as nearby bays and estuaries. By reducing Seadrift Lagoon’s green crab population, we hope to reduce predation on native species and reduce the supply of green crab larvae able to disperse to other sites.

Since 2009, researchers from the Smithsonian Environmental Research Center (SERC), Portland State University, and the University of California, Davis have been working with community volunteers to remove the crabs. The team of volunteers includes home owners and renters in the Seadrift community as well as high school and college students and members of other research and government agencies. Kiren Niederberger, the manager of the Seadrift Association, and local home owners such as Gail Graham and Larry Crutcher have been a critical part of our effort, providing access and assisting with our research in many ways. Volunteers venture out into the lagoon during three consecutive seasons, rain or shine, in hopes of trapping these invasive crabs. Collapsible traps are baited and laid across six transects (each approx. 150m long), with three transects on each side of the lagoon. That amounts to 90 traps set every trapping day. When the traps are collected the following day, crabs are bagged and frozen, then donated to Gospel Flat Farm, a local farm in Bolinas CA where they become compost. We have been told by the farm owners that the green crabs make for great crop fertilizer due to the large amounts of calcium in their exoskeleton combined with nitrogen in the tissue.

If you would like more information on the green crab project outside of Seadrift as well as data from different sampling efforts all up and down the west coast, see the Smithsonian's Green Crab Watch website at

Fighting European Green Crabs in Seadrift Lagoon. SERC, 2011. Web. 08 August 2014.