Cancer antennariusPacific rock crab

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Geographic Range

Cancer antennarius is found in intertidal waters off of the Pacific coast of North America. Areas between San Francisco, California and Baja California, Mexico are where the crab is most abundant, though Sequim, Washington marks the northern range limit (Carroll, 1989).

Habitat

The habitat of C. antennarius ranges from the low intertidal zone to depths in excess of 100 meters. The animal is found on both sandy and rocky substrates, though the rocky environment seems to be preferred. During low tide, C. antennarius is often seen under rocky overhangs and deep within crevices (Carroll, 1989).

Physical Description

Adults can have a carapace width of up to 155 mm, though females never exceed a width of 145 mm. The carapace is widest at the eighth, of nine, anterolateral teeth. The dorsal coloration is usually a deep red or brown, although this can vary to shades of orange or gray. The ventral side is white, with characteristic red spotting. The powerful claws are black-tipped, and the walking legs are almost always hairy. The latter trait is more common in females. The first antennae of C. antennarius are located between the eye stalks, and are distinctively long compared to others in this genus. As with all members of the Cancer genus, males have a more slender, pointed abdomen than do the females (Carroll, 1989; Mohler et al., 1997).

Reproduction

Mating most commonly occurs in the spring and fall. The process is carried out after the female molts, and while her shell is in a soft condition. Mating is stimulated by the release of a female pheromone. The males latch onto the females, and stay in that position until the shell of the female has hardened. During the courtship, a spermatophore is placed within the female. The sperm within this packet can be utilized for multiple spawnings. The spermatophore hardens within the female's reproductive tract, thus preventing other males from fertilizing her eggs. The eggs are extruded eleven weeks after the mating, and are fertilized internally as the female releases them. After a period of 7-8 weeks, the larvae hatch from the orange-colored mass of eggs. The larvae progress through six stages of growth, and are planktonic while doing so. Ocean currents cause the larvae to become widely distributed over the continental shelf. It is not until the last stage of larval growth that the animal moves inshore (Carroll, 1989).

Behavior

Few studies have been done on the behavior of Cancer antennarius. The relatively few tag and recapture studies indicate that this animal rarely travels more than a few kilometers from the site at which it is released. Trapping studies suggest that C. antennarius does exhibit some degree of onshore-offshore movement, although this phenomenon has not been fully examined. The movements in question are thought to be regulated by the animal's molting cycle. The molting process is governed by steroid hormones called ecdysteroids. These hormones are secreted by glands known as Y-organs. Small adults molt every 5-8 months, whereas larger individuals molt every 12-18 months (Carroll, 1989; Spaziani, 1989).

Food Habits

Cancer antennarius feeds by means of scavenging and predation. The animal's diet consists of a variety of bivalves, snails and echinoderms, as well as other crustaceans such as hermit crabs. I have personally kept a number of these animals, and have fed them a diet of shrimp and squid. This mixture seems to be quite suitable for the animal in an aquarium setting. C. antennarius is quite sensitive to the odor of food in the water, and this ability serves as a major means of locating food.

Animals that prey upon adult C. antennarius include sea otters, sharks, octopuses, and large sea bass. The animal is most vulnerable to attack after it has molted. At this time, the shell is soft, and the animal has little protection against predators. Juvenile members of this species are preyed upon by a variety of benthic fishes, including, but not limited to, scorpionfish, cabezon, sand bass, and rockfishes. The polychaete worm Iphitime holobranchiata is known to infest the gills of this particular rock crab, and the infestation is sometimes lethal (Carroll, 1989).

Economic Importance for Humans: Positive

With a taste that is reportedly similar to that of the Dungeness crab, Cancer antennarius is fished both commercially and recreationally. The industry is minor, however, when compared to the fishery of Cancer magister, the Dungeness crab. Most fishing of C. antennarius is centered in California, and localized overfishing does occur (Carroll, 1989).

Economic Importance for Humans: Negative

There is no known negative impact.

Conservation Status

The only known conservation efforts surrounding Cancer antennarius are centered in the fishing industry. State agencies impose catch limits on the crab, both for quantity and size (Carroll, 1989).

Other Comments

As noted above, I have kept numerous individuals of this species, and have found them to be loving and entertaining companions. Cancer antennarius requires little care, and the environmental requirements are minimal. An aquarium size of 80-100 liters is ideal for a pair. Numerous rocks, (of a large size), should be provided, allowing for both shelter and privacy. The animals should be given ample amounts of time in which the environment is darkened, for this is when they are most active. I have always kept the animals at a temperature range of 8-15 degrees C., so a water chiller is absolutely necessary. A feeding regimen of one large shrimp per animal, (at 3 day intervals), has always been followed. An occasional substitute of squid adds variety to the diet. Care should be taken to thoroughly thaw the food, for C. antennarius will have nothing to do with a frozen piece of shrimp. I have learned that with enough patience and handling, this animal becomes quite docile to the touch, and will often sit still in the keeper's hands. Keeping the animal out of the water for long periods should be avoided, however, due to the fact that the animal "prefers" to be submerged. For anyone thinking of acquiring a crab as a pet, I strongly recommend this species if you have the appropriately-sized aquarium and a water chiller.

Contributors

Andy Cameron (author), Western Oregon University, Karen Haberman (editor), Western Oregon University.

Glossary

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

benthic

Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

coastal

the nearshore aquatic habitats near a coast, or shoreline.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

native range

the area in which the animal is naturally found, the region in which it is endemic.

References

Carroll, J., R. Winn. 1989. Species profiles: life histories and environmental requirements of coastal fishes and invertebrates (Pacific Southwest)--brown rock crab, red rock crab, and yellow rock crab.. U.S. Fish and Wildlife Service Biological Report, 82(11.117): 1-16.

Mohler, J., D. Fox, B. Hastie. 1997. Guide to Oregon's Rocky Intertidal Habitat. Newport, OR: Oregon Department of Fish and Wildlife.

Spaziani, E., H. Rees, W. Wang, R. Watson. 1989. Evidence that Y-Organs of the crab Cancer antennarius secrete 3-dehydroecdysone. Molecular and Cellular Endocrinology, 66(1989): 17-25.