Pacific rock crab

Romaleon antennarium

Pacific rock crab

Romaleon antennarium

Other Common Names
Common rock crab, spot-bellied rock crab, California rock crab, brown rock crab. Sometimes called the red rock crab, though this common name is preferred for Cancer productus

Rocky Coast

Other Common Names

Common rock crab, spot-bellied rock crab, California rock crab, brown rock crab. Sometimes called the red rock crab, though this common name is preferred for Cancer productus

At the Aquarium

Rocky Coast

Appearance

This crab has black-tipped claws and a spine on the wrist. Males have larger claws than females. Its carapace is purplish-red to brick red to reddish-brown, while the underside of the shell is a pale yellow with reddish-purple spots. This crab has a wide, fan-shaped carapace that is at least 1.5 times as wide as it is long, and mostly smooth. The rough walking legs usually have hairs, especially in females and juveniles. Has long and stout paired antennae between the eyes.

Habitat

Intertidal to subtidal depths of nearly 300 feet, but usually occurs in waters less than 148 feet deep. Can be found in among rocky areas and pilings in estuaries, rocky habitats, kelp beds, on gravel bottoms, and sometimes on sandy bottoms.

Diet

Predator and scavenger; prey includes bivalves, snails, echinoderms, and other crustaceans

Life History

A female releases a pheromone in her urine before she molts, which stimulates a male to latch onto her and start carrying her around. Mating occurs just after the female molts, while her new shell is still soft. A male will place a spermatophore in the female and she can use the sperm in this packet over multiple spawnings. The spermatophore hardens inside of her reproductive tract and 11 weeks after mating, the eggs get fertilized as the female releases them to her abdominal flap. She broods the orange-colored mass of eggs for 7-8 weeks. During this time, the spongy-looking egg mass darkens in color as the developing crab embryos absorb the yolk in the eggs. A single egg mass contains 410,000 to 2,790,000 eggs. Then the larvae hatch and start life as plankton, feeding and growing, moving through 6 growth stages, while also dispersing over the continental shelf. After the last larval stage, the crab moves inshore.

Males can reach a carapace width of at least 6.1 inches, while female maximum carapace width is 5.7 inches. They can live up to 7 years.

IUCN Status

Not Evaluated

Ecosystem & Cultural Importance

Pacific rock crabs are eaten by sea otters, sharks, octopuses, and large sea bass. Pacific rock crabs are commercially and recreationally fished.

British Columbia to Baja California, Mexico

You are most likely to find juvenile pacific rock crabs while tidepooling, hiding in rock crevices or beneath algae. You might also pull up pacific rock crabs while crabbing in the bay.

Smaller adults will molt every 5-8 months while larger adults molt every 12-18 months. Crabs grow at each molt, with an increase of 7- 26% in width and 50- 70% in body weight for Pacific rock crabs. Crabs are most vulnerable to predation after molting while their shell is still soft.

The claws of rock crabs are powerful and enable adults to crush thick-shelled prey such as snails and cockles.

Citations & Other Resources

Animal Diversity Web
California Fish and Wildlife Marine Species Portal
Carroll, Jay C., and Richard Neil Winn. Species Profiles: Life histories and environmental requirements of coastal fishes and invertebrates (Pacific Southwest): brown rock crab, red rock crab, and yellow crab. No. 4. US Army Corps of Engineers, Waterways Experiment Station, Coastal Ecology Group, 1989.
Invertebrates of the Salish Sea
Oregon Department of Fish and Wildlife

Pacific rock crab

Pacific rock crab

Other Common Names

At the Aquarium

Appearance

Habitat

Diet

Life History

IUCN Status

Ecosystem & Cultural Importance

Citations & Other Resources

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