Dungeness Crab

Dungeness crab were named after a fishing town on the coast of Washington. Only the males are harvested, the females are thrown back into the water.

A tagging study was conducted by the California Department of Fish and Game. This study showed that crabs reared in the San Francisco Bay grew about twice the rate as ocean-reared crabs. The average carapace was appoximately 100 millimeters after one year. The hypothesis is that warmer bay temperatures and increased food availability is resposible for the rapid growth.

Dungeness crabs are affected by many insecticides. The insecticide carbaryl, also known as Sevin, is particularly toxic to the Dungeness crab. Other toxins include other insecticides and fungicides as well as ammonia. Urban pollutants such as heavy metals, PCB's and hydrocarbons also affect the Dungeness crab. Runoff of pesticides and herbicides affect the Dungeness crab populations as well. Dungeness crabs are not endangered, however, these chemicals can kill or upset the health of Dungeness crab populations.

US Federal List: no special status

CITES: no special status

Dungeness carbs are an important commercial shellfish. Male crabs are harvested along the coast of North America from Alaska to California. The fishery is worth tens of millions of dollars, due to the thousands of crabs caught annually.

Positive Impacts: food

Cancer magister eat a variety of marine invertebrates and fish. As juveniles, the Dungeness crabs feed on fish, shrimp, molluscs and crustaceans. Adults feed on bivalves, crustaceans and fishes. The crabs are able to open shells by chipping away at them with their heavy pinching claws.

Animal Foods: carrion ; mollusks; aquatic crustaceans; zooplankton

Primary Diet: carnivore (Insectivore , Eats non-insect arthropods)

Cancer magister, commonly known as Dungeness crab, is found in the costal waters from Point Concepcion, California, to the Pribilof Islands, Alaska. The Dungeness crabs inhabit the estuaries from Morro Bay, California, to Puget Sound, Washington.

Biogeographic Regions: pacific ocean (Native )

Dungeness crabs are found on the Pacific coast in sandy bottoms below the tidal mark. They can also be found at lowtide in sandy or muddy bays where there is a good growth of eel grass. Dungeness crabs are intolerant of low dissolved oxygen conditions. Also, even low amounts of ammonia are toxic to the crabs. Dungeness crabs also tend to grow better in water that is above six degrees Celsius (Kozloff 1973).

Habitat Regions: temperate ; saltwater or marine

Aquatic Biomes: benthic ; coastal ; brackish water

Other Habitat Features: estuarine

Cancer magister is a decapod. Decopods' thoracic segment is fused with that of the head, to form the cephalothorax, which is covered by a carapace. The Dungeness crab has five pairs of thoracic legs. The first pair of legs is larger then the last four and has pinching claws. Cancer magister is a walking crab and therefore, the last pair of legs is adapted for walking. It has a flat and broad body, oval in shape. The anterior margin of the carapace has nine small teeth on each side, forming an elliptical curve. At the end of the curve, a large, pointed tooth projects directly outward. From this tooth, the carapace slopes backward, forming a narrow posterior end. Males range from 18 to 23 centimeters (about 7 to 9 inches)in width and 10 to 13 centimeters (4 to 5 inches) long. The color of the carapace is reddish-brown, fading towards the back. The legs and ventral side are yellowish.

Range length: 10 to 13 mm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Seals, sea lions, and a variety of fish eat Dungeness crabs.

Males attract the females by use of pheromones, which are chemical scents. During mating, the male crabs clasp the female so that the undersides of each are close. The male's breeding structures place the sperm into the female's body. This is only possible when the female is soft shelled, right after molting. This lasts less than thirty minutes. Mating occurs in near-shore costal locations, outside of estuaries. The eggs are not fertilized and spawned until the fall, following the summer breeding. After fertilization, about half a million to one million eggs are attatched to the female's abdomen. These eggs are brooded there until spring. The larvae are planktonic and use tidal currents to travel into estuaries. The larvae pass through six stages over a 105 to 125 day period. The last two stages are zoea and megalopa. Zoea have a jointed abdomen and a spined carapace behind the head with large eyes. Megalops have big eyes, an extended abdomen, elongated carapace and swimming legs. After the first molting, the form changes to that similar to the adults. Growth after this point occurs by shedding its shell, molting, at certain periods of time, until it reahces full growth (Headstrom 1979, Mash 1975).

Most common in sand or muddy-sand bottoms in subtidal regions, often in or near eelgrass beds. Often partly buries itself in the sand.

Geographical Range: Occurs from Alaska to Santa Barbara, California.

Depth Range: Lives from intertidal to a depth of 230 m.

A Red-brown to purple carapace with a spine-tipped edge on the front half; contains ten teeth on the anterolateral margins. The tenth tooth is the largest and is at the widest portion of the carapace. There are no teeth on the posterolateral margins. The chelipeds are purple to brownish at the base and the chelae are white at the tips. The carpus, propodus, and dactyl of the chelipeds have spiny ridges. The rear legs are more flattened than are those of most local cancer crabs, and are fringed with setae. Some hairlike setae can also be found on the underside of the carapace. This species alone accounts for the large majority of all crabs taken commercially in the Pacific Northwest. It is the largest cancer crab in North America. Width of carapace up to 25 cm in males and 18 cm in females.

How to Distinguish from Similar Species: The most similar-appearing local species is Metacarcinus gracilis, which has similar coloration and white claw tips as does this species. However, it has a distinct tooth behind the widest point of the carapace and has no spiny ridges on the carpus, propodus, and dactyl of the chelae. It also does not grow as large. Cancer productus, also often found intertidally and subtidally in the Pacific Northwest, has black tips to the dactyls of the chelae.Note: Species formerly in genus Cancer have been recently subdivided into several genera. Of our local genera, Cancer, Romaleon, and Metacarcinus have a carapace wider than long plus only scattered setae on the carapace margins and legs while Glebocarcinus has a carapace of approximately equal length and width, often with granular regions and with setae along the edges; and setae on the outer surface of the chela as well as on the legs. Metacarcinus can be distinguished from Cancer because Metacarcinus has anterolateral carapace teeth which are distinct and sharp plus the male has a rounded tip to the telson, while Cancer has anterolateral carapace teeth which are low and lobed, separated by deep fissures plus the male has a sharply pointed telson. Romaleon can be distinguished from Cancer and Metacarcinus because it has a distinct tooth on the anterior third of the posterolateral margin of the carapace while the other two genera do not.

Biology/Natural History: This crab is the largest edible crab from Alaska to California, making this species important for fisheries commercially and economically. There appear to be five subspecies in California alone. The female Dungeness crab can lay up to 2.5 million eggs and can live up to at least 6 years. Females can store sperm received during one mating season and use it during the next season. This species is a carnivore that feeds on more than 40 different species including small clams, oysters, fish, shrimp, worms and according to recent studies even feeds on Velella velella nematocysts. The larvae of this species is often attached to the bells of jelly fishes and to their tentacles; these larvae feed on the gonozooids, and by doing so gain protection from pelagic fish predators and are transported to juvenile crab habitats nearshore as long as associated with the cnidarian. Dungeness crab larvae feed primarily on zooplankton, however phytoplankton are also eaten. The larvae are crepuscular migrators, being found near the surface at dawn and dusk but deeper in midday and midnight. The stage 1 zoeae are nearest the surface with later zoeal stages in deeper water. In spring, larvae of this species may be advected north along the coast as far as Alaska. In springtime, adults of this crab can be found buried in sand or in tidepools, where it can hide and wait for its new shell to harden. On average, males will cover more ground in an hour than females, and ovigerous females move less than nonovigerous females or males. Near Vancouver Island, adults have more epibionts than do juveniles. Common epibionts include barnacles on the dorsal surface, green, red, and brown algae, tube-dwelling polychaetes, hydrozoans, bryozoans on any region of the carapace. A few had sponge, tunicate, or mollusk epibionts. Feeding in ovigerous females is greatly reduced below that of non-ovigerous females. Females are able to survive an entire winter without feeding, at least in the laboratory. Both juvenile and adult crabs may sometimes be cannibalistic. Dudas et al. found that the common local cancer crabs Metacarcinus magister and Cancer productus preferred the thin-shelled introduced varnish clam Nuttallia obscurata to the thicker-shelled clams Leukoma staminea and Venerupis philippinarum if access to all was equally easy. However, Nuttallia obscurata typically lives deeper in the sediment than do Leukoma staminea or Venerupis philippinarum. If they had to dig for them, Metacarcinus magister still ate more Nuttallia obscurata than it did of the other clam species, but C. productus' preference switched to Leukoma staminea and Venerupis philippinarum. Jensen and Bentzen found that the egg clutches of females frequently have multiple paternity. Adult females molt once a year and mate with one male per molt. They can store sperm for up to 2.5 years.The hoplonemertean worm Carcinonemertes errans, an ectosymbiont and egg parasite in Metacarcinus magister, is in turn eaten by a Riserius sp nemertean whose larvae have previously been classified as pilidium recurvatum