The Dungeness crab (Metacarcinus magister) is a commercially valued crustacean along the Pacific coast of North America. Understanding their habitats is important for their biology and sustainable populations. This involves recognizing their geographical spread, the specific aquatic conditions they need, and how their habitats change throughout their life cycle.
Pacific Coast Distribution
Dungeness crabs are native to the Pacific coast of North America, where they are found across a wide geographical range. Their distribution extends from the Aleutian Islands in Alaska, southward to Point Conception near Santa Barbara, California. On occasion, individual crabs have been observed as far south as Magdalena Bay in Baja California Sur, Mexico.
These crabs inhabit coastal waters, including bays and estuaries, throughout this extensive area. Their presence is particularly notable in the cooler, temperate waters of the Pacific Northwest. The species gets its common name from Dungeness Spit in the Strait of Juan de Fuca, Washington, which shelters a shallow bay where these crabs live.
Essential Aquatic Conditions
Dungeness crabs prefer soft substrates like sand or mud, often interspersed with shell debris or eelgrass beds. They can be found from shallow intertidal zones down to significant depths. They are found as deep as 750 to 800 feet (228 to 244 meters), but are most commonly found in waters ranging from the intertidal zone to about 300 feet (91.4 meters).
Adult Dungeness crabs tolerate water temperatures between 38°F and 65°F (3°C and 18°C). Their salinity tolerance ranges from 11 to 35 practical salinity units (PSU), though they prefer salinities between 25 and 32 PSU. Larval stages are more sensitive, requiring temperatures between 50°F and 57°F (10°C and 14°C) and exhibiting less tolerance for lower salinities.
Habitat Shifts Across Life Stages
The Dungeness crab’s habitat use changes throughout its development. Their life cycle begins with pelagic larval stages, known as zoea and megalopa, that drift in ocean currents. These free-swimming larvae undergo vertical migration, typically moving to shallower depths at night and deeper during the day. This larval development can last for several months, with some remaining in the larval stage for up to a year in colder regions like Alaska.
After the larval stages, juvenile crabs settle onto the seafloor, utilizing shallow, protected environments. Estuaries, bays, and intertidal areas with features such as eelgrass beds, shell fragments, or other structures provide important nursery habitats, offering food and refuge from predators. As they mature, Dungeness crabs migrate to deeper, offshore waters, where adult crabs reside on sandy or muddy bottoms. Here, they feed, molt, and reproduce.