Biology Reference
In-Depth Information
Dungeness Crab
The native Dungeness Crab carries a distinctive V on its carapace, or shell,
and has smaller claws but more edible flesh than the brilliant Red Rock
Crab. Observers can tell a Dungeness (
Cancer magister
) from similar-
looking species by examining the pincer-shaped claws. Rock Crabs have
black-tipped claws; Dungeness have white ones. The sharp points of their
remaining six legs are tipped with a biomaterial harder than acrylic glass.
Because the material resists dulling, the animals can scuttle about for
many weeks and still have feet sharp enough to cling to slimy surfaces.
Dungeness Crabs are present from the Aleutian Islands to Santa Bar-
bara, but San Francisco Bay is at the southern edge of their range. The life
cycle of the Dungeness Crab starts outside the Golden Gate, with hard-
shelled males mating with soft-shelled females sometime between March
and May each year. The following fall, each mated female produces up to
two million eggs, carrying them as a spongelike mass under a belly flap
until they hatch in December or January. The offspring first emerge as tiny
plankton-eating larvae. They must grow through several life stages before
they begin to resemble crabs around April to June. At this point, the young
crabs swarm through the Golden Gate in large numbers, likely following
chemical cues such as spring freshwater outflows.
Once they enter the Gate, young crabs seek out areas with lower salini-
ties than the ocean, and they concentrate in the shallows. Juvenile Dunge-
ness Crabs favor the shallow, soft, food-filled bottom of San Pablo Bay and
nearby tidal marshes. After summering in San Pablo Bay, they follow that
bay's deeper channels in their fall migration to the Central Bay and ocean.
By that point, most will have grown to about four inches across.
To grow, Dungeness and other crabs must shed or molt their exoskel-
etons. These empty shells, called “ghosts,” often wash up on beaches, where
Dungeness Crab on sale at Fisherman's Wharf, San Francisco. (Ariel Rubissow
Okamoto)
