The Dungeness crab (Metacarcinus magister) makes up one of the most important seafood industries in the range it inhabits along the west coast of North America. It typically grows 20 cm (7.9 in) across and inhabits eelgrass beds and sandy bottoms. Its common name comes from the Dungeness Spit in the Strait of Juan de Fuca, Washington, United States, which shelters a shallow bay inhabited by the crabs.
The carapace widths of mature Dungeness crabs may reach 10 inches, or 25.4 centimeters, but are typically 6–7 inches, or approximately 15–18 centimeters.
Dungeness crabs have a wide, long, hard shell, which they must periodically molt to grow; this process is called ecdysis. They have five pairs of legs, which are similarly armored, the foremost pair of which ends in claws the crab uses both as defense and to tear apart large food items. The crab uses its smaller appendages to pass the food particles into its mouth. Once inside the crab's stomach, food is further digested by the "gastric mill", a collection of tooth-like structures. M. magister prefers to eat clams, other crustaceans and small fish, but is also an effective scavenger. Dungeness crabs can bury themselves completely in the sand if threatened.
The Dungeness crab is named after the Dungeness Spit in the Strait of Juan de Fuca, Washington, United States, which shelters a shallow bay inhabited by the crabs. Its typical range extends from Alaska's Aleutian Islands to Point Conception, near Santa Barbara, California, while it is occasionally found as far south as Magdalena Bay, Baja California Sur, Mexico.
A genetic analysis of adult Dungeness crabs indicated that there is one population across the California Current System, but it is likely that interannual variation in physical oceanographic conditions (such as ocean circulation patterns) influence larval recruitment among regions, causing genetic diversity to change through time.
Mature female crabs generally molt in late spring, although exact timing varies with location. Mating occurs immediately after the female has molted and before the new exoskeleton hardens. Males are attracted to potential mates by pheromones present in the urine of females. Upon locating an available female, the male initiates a protective premating embrace that lasts for several days. In this embrace, the female is tucked underneath the male, oriented such that their abdomens touch and their heads face each other. Mating occurs only after the female has molted, and the female signals her readiness to molt by urinating on or near the antennae of the male. The female extrudes the eggs from her body several months later; however, they remain attached under her abdomen for three to five months until they hatch. Young crabs are free-swimming after hatching, and go through five zoeal larval stages and one megalops stage before settling to the bottom in their first juvenile stage. The free-swimming stages take three months to a year. Sexual maturity is reached after about 12 molts or two years.
Juvenile crabs develop in eelgrass beds and estuaries where salinity levels tend to be low. The hyposaline conditions of the estuaries are lethal to some of the crab's symbionts, such as Carcinonemertes errans which consumes a brooding female's live eggs. Dungeness crabs surveyed in Coos Bay were less likely to be infected by C. errans and have fewer worms present on their carapace when inhabiting less saline waters farther inland.
