Dungeness crabs (Cancer magister) occur throughout Washington waters, including the outer coast (mostly in coastal estuaries) and inland waters. Dungeness crabs use different habitats throughout their life cycle: as larvae they are planktonic, as juveniles they are found in intertidal mixed sand or gravel areas with algae or eelgrass (Holsman et al. 2006) and as adults they are found in subtidal or intertidal areas on sand, mud, or associated with eelgrass beds. Bare habitats are infrequently used by juveniles, most likely due to a lack of refuge from predation and decreased food abundance (McMillan et al. 1995). Vegetated, intertidal estuaries appear to be important nursery habitats for young crabs (Stevens and Armstrong 1984); older crabs have been shown to move progressively into unvegetated subtidal channels (Dinnel et al. 1986, Dethier 2006).
As predators and scavengers, Dungeness crabs feed upon a broad range of prey including small mollusks, crustaceans, clams, and fishes. They also prey for a wide variety of taxa, which varies with their life history stage. Larvae are preyed upon by coho and Chinook salmon and rockfishes; juveniles by a wide variety of fishes; and adults by fishes, seals, octopuses, and each other (generally when molting) (Orcutt et al. 1976, Reilly 1983, Dethier 2006).
Threats to Dungeness crabs include: low dissolved oxygen, variation in temperature and salinity, fisheries, habitat alteration or loss, and pollutants such as insecticides, hydrocarbons from oil spills and heavy metals. Because juvenile crabs rely on estuarine habitats and are also potentially more sensitive to toxins, early life history stages are likely to be more influenced by human activities (Dethier 2006).