This cancer crab has a dark
tip to the dactyl of the chela (photo).
carapace is much wider than it is long, and its dorsal surface is
smooth and not covered with large bumps or tubercles. The
of the chela usually has several tubercles (photo).
The widest point of the carapace is at the 8th (next to the last)
tooth (photo). Dorsal carapace is usually brick red, and up
cm wide in males and 17 cm in females. The series of five
between the eyes are nearly equal in size and extend slightly farther
than does that of most cancer crabs, leading to the productus
the name. The dactyls of the walking legs have short
The carapace color pattern of juveniles is very different from that of
adults (photo), often white
or with red and white
Cancer productus Randall, 1839
Common name(s): Red rock crab, Red
crab, Red cancer crab
|Cancer productus, about 12 cm
carapace width, at Sares Head
|(Photo by: Dave Cowles
How to Distinguish from
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
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,
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
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
because it has a distinct tooth on the anterior third of the
posterolateral margin of the carapace while the other two genera do
Alaska to San
Low intertidal to 90
Rocky and soft bottoms.
Most common around rocks. Often found half-buried in sand
during the day; more active at night.
include sand and kelp bass and sculpin (on juveniles) and seabirds such
as gulls and pigeon guillemots. Prey include barnacles and
crabs, amphipods, sea cucumbers, polychaetes, many other intertidal
as well as dead fish. At least 42 prey species have been
Are an important threat to commercial oyster beds. Crabs
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
who is preparing to molt, by holding her under his abdomen.
may last for several weeks until she molts. He then guards
her exoskeleton hardens again. Gravid females may be found
to June. Females may carry from 172,000 to 597,000 eggs on
of the abdomen. Males overwinter in shallow areas, while
seem to overwinter in deeper water. Red rock crabs cannot
and so are not found in areas of low salinity. Near Vancouver
adults have more epibionts than do juveniles (McGraw,
2006). Common epibionts include barnacles
crenatus) on the dorsal surface, green, red, and
brown algae (especially
on the antennae), tube-dwelling polychaetes (mainly on the ventral
hydrozoans (mainly on ventral surfaces and limbs), bryozoans
membranacea) on any region of the carapace. A few
tunicate, or mollusk epibionts.
et al. (2005) found that the common local cancer crabs Metacarcinus
magister (Dungeness crab) and Cancer
the thin-shelled introduced varnish clam Nuttallia
obscurata to the thicker-shelled clams Leukoma
staminea and Venerupis
philippinarum if access to all was equally
obscurata typically lives deeper in the sediment
than do Leukoma
staminea or Venerupis
philippinarum. If they had to dig for
magister still ate more Nuttallia
obscurata than it did of the other clam species,
but C. productus'
preference switched to Leukoma
staminea and Venerupis
and Fairbanks, 1966
and Carlton, 1975
and Brusca, 1978
and Laurent, 1979
and Snook, 1955
and McConnaughey, 1985
et al., 1980
and O'Clair, 1998
et al., 1985
Sarah E., Iain J. McGaw, and John F. Dower, 2005.
predation on native and introduced bivalves in British
Journal of Experimental Marine Biology and Ecology 325:1 pp 8-17
Dufur, Peter L., Brian R. McMahon, and Charles E. Booth,
Analysis of hemolymph oxygen levels and acid-base status during
'in situ' in the red rock crab, Cancer productus.
Bulletin 165: 582-590
Iain J., 2006. Epibionts of sympatric species of
in Barkley Sound, British Columbia. J. Crustacean Biology
P.K.L., D. Guinot, and P.J.F. Davie, 2008.
Systema Brachyurorum: part I. An annotated checklist of
brachyuran crabs of the world. Raffles Bulletin of Zoology,
Supplement 17 pp. 1-286 (Clicking on link will load a pdf of the long
Reese, J.E., and C. P. Mangum, 1994. Subunit
composition and O2
binding of the crustacean Hemocyanins: Interspecific
Biological Bulletin 187: 385-397
Frederick R. and Peter K.L. Ng, 2012. What is
Cancer? Journal of Crustacean Biology 32:4 pp. 665-672
C.F. and R.M. Feldmann, 2000.
Re-evaluation of the Cancridae Latereille, 1802 (Decapoda: Brachyura)
including three new genera and three new species.
to Zoology 69:4 pp. 223-250
Wekell, J.C., R. M. Lorenzana, M. Hogan, and H. Barnett,
Survey of paralytic shellfish poison and domoic acid in Puget Sound
gastropods. J. Shellfish Research 15(2): 231-236
General Notes and
Observations: Locations, abundances,
In seawater tanks this species will readily attack most
including smaller crabs, shrimp, clams, snails, hermit crabs,
They crack them into pieces with their powerful claws. This
should not be kept with other species.
The tip of the dactyl on the chela of Cancer productus
and the propodus has several tubercles, some of which are usually
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
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
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
|This small juvenile Cancer
productus, found subtidally
at Admiralty Beach, often assumes an unusual defense posture with the
held lengthwise to the body when disturbed (left) rather than crosswise
to the body as is usually seen (right). Both photos are of
crab, which is the same individual as the crab at left in the table
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
(lower) before they molt. The carry them underneath
them until the female molts. At that time sperm transfer
The male continues to guard the female until after her new exoskeleton
has hardened, then releases her.
Underwater photo by Kirt Onthank, June 2007
Authors and Editors of Page:
Dave Cowles (2005): Created original page