Cancer productus Randall, 1839 Common name(s): Red rock crab, Red crab, Red cancer crab
Synonyms:  Platycarcinus productus, Cancer perlatus
Phylum Arthropoda  Subphylum Crustacea   Class Malacostraca    Subclass Eumalacostraca     Superorder Eucarida      Order Decapoda       Suborder Pleocyemata        Infraorder Brachyura         Superfamily Cancroidea          Family Cancridae
	Cancer productus, about 12 cm carapace width, at Sares Head
	(Photo by: Dave Cowles September 2005)

How to Distinguish from Similar Species:  The other large, common cancer crab species in the Rosario area is C. magister, which does not have a dark tip to the dactyl of the chela, and its carapace is widest at the 10th and last lateral tooth.  C. antennarius has red spots on the underside of the carapace.

Note:  Species formerly in genus Cancer have been recently subdivided into several genera (Ng et al., 2008; Schweitzer and Feldmann, 2010).  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 (Schram and Ng, 2012).  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.

Geographical Range:  Alaska to San Diego

Depth Range:  Low intertidal to 90 m

Habitat:  Rocky and soft bottoms.  Most common around rocks.  Often found half-buried in sand under rocks during the day; more active at night.

Biology/Natural History:  Predators include sand and kelp bass and sculpin (on juveniles) and seabirds such as gulls and pigeon guillemots.  Prey include barnacles and smaller crabs, amphipods, sea cucumbers, polychaetes, many other intertidal invertebrates, as well as dead fish.  At least 42 prey species have been noted.  Are an important threat to commercial oyster beds.  Crabs raised on thick-shelled species such as Mytilus californianus developed even stronger claws.  Mating occurs in summer after a female has molted.  Males will often guard a female who is preparing to molt, by holding her under his abdomen.  This may last for several weeks until she molts.  He then guards her until her exoskeleton hardens again.  Gravid females may be found from October to June.  Females may carry from 172,000 to 597,000 eggs on the pleopods of the abdomen.  Males overwinter in shallow areas, while females seem to overwinter in deeper water.  Red rock crabs cannot osmoregulate and so are not found in areas of low salinity.  Near Vancouver Island, adults have more epibionts than do juveniles (McGraw, 2006).  Common epibionts include barnacles (especially Balanus crenatus) on the dorsal surface, green, red, and brown algae (especially on the antennae), tube-dwelling polychaetes (mainly on the ventral surfaces), hydrozoans (mainly on ventral surfaces and limbs), bryozoans (especially Membranipora membranacea) on any region of the carapace.  A few have sponge, tunicate, or mollusk epibionts.

Dudas et al. (2005) found that the common local cancer crabs Metacarcinus magister (Dungeness crab) 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 (2024) also reported observations of C. productus capturing and eating fish. 

References:

General References:
  Brusca and Brusca, 1978
  Gotshall, 1994
  Gotshall and Laurent, 1979
  Harbo, 1999
  Hinton, 1987
  Jensen, 1995
  Johnson and Snook, 1955
  Kozloff, 1993
  McConnaughey and McConnaughey, 1985
  Morris et al., 1980
  Niesen, 1994
  Niesen, 1997
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985
  Sept, 1999

Scientific Articles:

Dudas, Sarah E., Iain J. McGaw, and John F. Dower, 2005.  Selective crab predation on native and introduced bivalves in British Columbia.  Journal of Experimental Marine Biology and Ecology 325:1 pp 8-17

Dufur, Peter L., Brian R. McMahon, and Charles E. Booth, 1983.  Analysis of hemolymph oxygen levels and acid-base status during emersion 'in situ' in the red rock crab, Cancer productus.  Biological Bulletin 165: 582-590

Jensen, Gregory C., 2024. Piscivory by the crabs Cancer productus Randall, 1840 and Pugettia producta (Radall, 1840)  (Decapoda: Brachyura: Cancridae, Epialtidae). Journal of Crustacean Biology 44:3 pp. ruae042. doi: 10.1093/jcbiol/ruae042

McGraw, Iain J., 2006.  Epibionts of sympatric species of Cancer crabs in Barkley Sound, British Columbia.  J. Crustacean Biology 26:1 85-93

Ng, P.K.L., D. Guinot, and P.J.F. Davie, 2008.  Systema Brachyurorum: part I.  An annotated checklist of extant brachyuran crabs of the world.  Raffles Bulletin of Zoology, Supplement 17 pp. 1-286 (Clicking on link will load a pdf of the long article)

Reese, J.E., and C. P. Mangum, 1994.  Subunit composition and O2 binding of the crustacean Hemocyanins:  Interspecific Relationships.  Biological Bulletin 187: 385-397

Schram, Frederick R. and Peter K.L. Ng, 2012.  What is Cancer?  Journal of Crustacean Biology 32:4 pp. 665-672

Schweitzer, C.F. and R.M. Feldmann, 2000.  Re-evaluation of the Cancridae Latereille, 1802 (Decapoda: Brachyura) including three new genera and three new species.  Contributions to Zoology 69:4 pp. 223-250

Wekell, J.C., R. M. Lorenzana, M. Hogan, and H. Barnett, 1996.  Survey of paralytic shellfish poison and domoic acid in Puget Sound predatory gastropods.  J. Shellfish Research 15(2): 231-236

Web sites:
 

In seawater tanks this species will readily attack most smaller animals, including smaller crabs, shrimp, clams, snails, hermit crabs, etc.  They crack them into pieces with their powerful claws.  This species should not be kept with other species.

The tip of the dactyl on the chela of Cancer productus is dark, and the propodus has several tubercles, some of which are usually arranged in longitudinal lines.

The carapace of Cancer productus has 10 teeth lateral to the eye.  The carapace is widest at the 9th tooth.

In this individual (live) one can see the fringes of setae on the legs.

This large male is holding a smaller female, in preparation for her molt.

Mating takes place after the female has molted.

 

Some of the color patterns possible on a Cancer productus juvenile.  Note the possible sequence of patterns from left to right as the crab grows larger.
Crab from subtidal, Admiralty Beach.  Photo by Dave Cowles July 2007	Photo by Dave Cowles July 2006	Crab at Keystone Ferry jetty, July 2007.  Photo by Bethany Reiswig

One of the color patterns possible on a Cancer productus juvenile.
 
 

This small juvenile Cancer productus, found subtidally at Admiralty Beach, often assumes an unusual defense posture with the chelae held lengthwise to the body when disturbed (left) rather than crosswise to the body as is usually seen (right).  Both photos are of the same crab, which is the same individual as the crab at left in the table above.  Photos by Dave Cowles, July 2007 Another juvenile, found near Rosario in 2021 An underwater photo by Kirt Onthank, Jule 2007 Since the female gonopores are hard during intermolt, mating cannot occur except during a molt.  Male crabs (upper) pick up female crabs (lower) before they molt.  The carry them underneath themselves, protecting them until the female molts.  At that time sperm transfer takes place.  The male continues to guard the female until after her new exoskeleton has hardened, then releases her. Underwater photo by Kirt Onthank, June 2007