Crabs have separate sexes, and copulation and direct sperm transfer are the rule.  Perhaps because of their inflexible exoskeletons, the copulatory partners wait until the female moults before sperm transfer is initiated.  The male senses through pheromones released by the female that her moult is imminent.  Then, to ensure that he will be the copulatory partner, he holds her in a close embrace known as amplexus (lit. “embrace” L.) until she moults.  After copulation, which involves the male inserting spermatophores (sperm packets) into the vagina of the female, the female begins to release photograph of SCUBA-diver holding 2 red rock crabs in copulatory amplexuseggs.  The interval between copulation and egg release varies from a few days to weeks depending upon species.  As they transit from gonad to genital pore the eggs pass through the sperm mass and are fertilised.  The eggs are sticky and are caught up on fine bristles on the female’s abdominal appendages.  She carries the eggs for several weeks until they hatch into free-swimming zoea (lit. “animal” G.) larvae.  There is a short-lived (hours or 1-2d) protozoeal (or prezoeal) and 5 planktonic zoeal stages. 

Immediately following Research Study 1 below, aspects of copulation, egg release, & larval stages are considered for several genera of west-coast crabs & relatives. Other topics on reproduction include LARVAL LIFE and SETTLEMENT, METAMORPHOSIS, & RECRUITMENT presented in other sections. For a review of crab larvae and life cycles see Hines1986 Bull Mar Sci 39 (2): 444.

Cancer productus in amplexus. It's hard to tell what's going on in the photo but,
first, identify the large male being held by the diver. It is facing the camera and
has over-exposed whitish parts on the limbs. Within its chelipeds is a much smaller
female being held abdomen-to-abdomen, with its reddish dorsal side facing the camera

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Research study 1

composite graph showing brood mass against body mass for 20 species of west-coast crabsWhat sets the limits on reproductive output in a crab?  Is it just body size or are other factors involved?  A large comparative study on reproductive variability in 20 species of marine crabs, including 10 from the west coast (shown in coloured labels on the graph), confirms that body size is the principal determinant of reproductive output, explaining 95% of variance in brood mass, 79% of variance in number of eggs per brood, 63% of variance in annual brood mass, and 74% of variance in annual fecundity.  Interestingly, allometric limitations on space available for yolk accumulation within an inexpansible body appear to be the main constraint on brood size.  Egg size increases slightly but significantly with increasing body size.  Size range of the 20 species used in the study span 4 orders of magnitude. 

Brood mass is strongly and positively correlated with body size for all 20 species (see graph).  Slopes of logarithmic regression plots of brood mass against body mass for the 20 species vary around an expected isometric value of 1 and, interestingly, a plot of the 20 regressions themselves is isometric (b = 1.04; see graph on Right). Overall, brood mass represents about 10% of body mass in these photograph of crabs Scyra acutifrons and Cancer magisterbrachyurans.  The author surmises that the constraint on brood size is directly related to body volume.  Ovaries have to compete for space with other body organs.  A similar plot of number of eggs per brood against body mass yields a negative allometric relationship.  Thus, small crabs (e.g., Scyra acutifrons: 0.1g) produce about 12,000 eggs . g-1 body mass per brood while large crabs (e.g., Metacarcinus magister: 100g) produce about 3,400 eggs . g-1 body mass per brood.  In absolute terms, a small Scyra produces about 150 eggs in a brood, while a large Cancer produces over 1 million eggs per brood.  Hines 1982 Mar Biol 69: 309.


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Copulation, egg release, & larval stages

  This topic is divided into sections on the genus Cancer, considered here, and ones on species in GENERA A-L and GENERA O-R, presented elsewhere.
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Metacarcinus & Cancer

Research study 1

photo showing scratch marks on the claw of a Dungeness crab resulting from holding the female during copulatory amplexus; photo courtesy Antan Phillips, DFO, NanaimoCopulation in crabs is a scratchy enterprise and you can tell from the presence of these “mating marks” on the inside of the claws of a male Dungeness crab Metacarcinus magister whether he has recently (white marks) or last year (yellow marks) been in copulatory amplexus.  Females are also marked during amplexus, but more along the front edge of the carapace.  Such mating marks may also be present on females of species such as tanner crabs Chionoecetes bairdi that reach a terminal moult but that still copulate in subsequent years to “top up” their supply of sperm. Photo courtesy Antan Phillips, DFO, Nanaimo.

NOTE  many decapod crustaceans, such as lobsters and cancrid crabs (Cancer spp.), moult at regular intervals until death.  Others, such as spider crabs, decorator crabs, tanner and snow crabs, and swimming (portunid) crabs moult to a certain size and then undergo one final terminal or pubertal moult, at which time an individual is a sexually mature adult and will not moult again

Research study 2

schematic showing life cycle of Dungeness crab Cancer magister
Eggs of Dungeness crabs Metacarcinus magister hatch to a short-lived larval form known as a protozoea.  This moults within a day or so to the first of 5 zoea stages.  The zoea larvae spend several weeks feeding on small zooplankters.  The final moult is to a megalopa stage, which is about 6mm in length.  The megalopae swim or cling to floating debris for their final drift onto shore and metamorphosis.  MacKay 1942 Bull Fish Res Bd Can 62: 1

NOTE  lit. “large husk” G.

Research study 3

graph showing size distribution of Dungeness crabs Cancer magisterphotograph showing difference between copulatory scratch marks and inter-male fighting marks on the claw of a Dungeness crab Cancer magisterBreeding of Dungeness crabs Metacarcinus magister in the islands of Haida Gwaii, British Columbia occurs in May-September and begins when the males are 110mm carapace width, or about 3yr of age (but sexual activity is not appreciable until a size of 140mm is reached).  Females are mature at 100mm carapace width, or about 2yr of age.  Copulation occurs with the post-moult female on her back and abdominal flaps of both partners flexed open.  The spermatozoa in a male crab are packaged into spermatophores.  In M. magister the spermatophores rupture after leaving the vas deferens and only free spermatozoa are found in the female’s spermathecae and around the oviducal openings.  After copulation the cavity of the oviduct seals by a secretion that hardens in contact with seawater. The sperm remain viable in the female’s spermathecae for several weeks or months until the eggs mature in the autumn.  As the eggs pass by the spermathecal openings in the paired oviducts they are fertilized, then extruded and attached to the setae of the innermost limbs of the pleopods.  Of 5,461 male crabs (ranging from 107-218mm carapace width) examined in the study, 27% are noted as having mating marks.  The author remarks that this is the first report of such mating marks in the scientific literature.  Males commonly fight for females, with the larger one usually winning.  Chelae and other body parts may bear damage from these fights, as indicated in the photo above Left. The author notes that the extent of mating marks on undersized males, therefore, may provide a useful index of the extent to which commercial harvesters exploit a crab population.  Butler 1960 J Fish Res Bd Can 17: 641. Photo courtesy Antan Phillips, DFO, Nanaimo.

NOTE  such marks are apparently not found on other cancrid species, such as C. pagurus (Europe), C. productus, or C. gracilis. It is not clear when reading these accounts whether scratch marks (mating marks) on M. magister are always caused by abrasion from the females or whether they include damage from inter-male fighting

Research study 4

photograph of Dungeness crabs Cancer magister copulatingphoto/schematic showing location of male gonopore in Dungeness crab Cancer magisterLaboratory observations of mating in Metacarcinus magister provide the following details of the copulatory act.  The male holds a pre-moulting female for a week or so, sternum to sternum, until she moults.  At some point during the latter stages of pre-copulatory amplexus the female flips rightside-up, preceded by her pinching the male’s eyestalks to make him relax his hold somewhat.  However, at no time does the male completely release the female during her moult.  Copulation occurs about 1.5h after the female moults, when the new exoskeleton has firmed somewhat, and with the female now back in a sternum-to-sternum position (i.e., upside-down).  photograph showing relationship of copulatory appendages with the vas deferens tip in a Dungeness crab Cancer magisterThe male carries the female for another 2d.  Extensive wear on the male’s chelae comes more from stroking the female during amplexus than from mating with several females. 

The male inserts his gonopods (a pair of reproductive appendages shown in the photos on the Left) directly into the female’s spermathecae (located in the vagina) and spermatophore transfer ensues.  Snow & Nielsen 1966 J Fish Res Bd Can 23: 1319.

The spermatophores move from the male's gonopores, located at the bases of the 5th walking legs (below the white arrow-head in upper photo on Left), into a groove formed by the juxtaposition of the paired gonopods. These appendages are shown separated in this view because the male's abdominal flap is opened to its fullest (the blue arrow shows how the posterior gonopod moves alongside the anterior one when the flap is partially closed as during copulation). In the lower photo on the Left the soft end of the left vas deferens is clearly visible and the gonopods are in proper alignment. When the gonopod pair is inserted into the female's gonopore, the spermatophores move from the vas-deferens opening, along the groove and into the female's vagina

Research study 5

The 5 zoeal stages and megalopal stage are described for Cancer productus collected at Humboldt Bay, California (cultured at 17oC).  Length change during development is from 2.5mm for Zoea I, to 5.5mm for Zoea V, to 6mm for the megalops.  The author notes 50% mortality during the moult from Zoea V to megalops, owing to difficulty experienced by the larvae in shedding their exoskeletons.  Trask 1970 Crustaceana 18: 133. Photo courtesy Iain McGaw, U Nevada.

NOTE  measured from the tip of the rostral spine to the end of the telson

photograph of red rock crab Cancer productus courtesy Iain McGaw, U Nevada drawing of first zoeal stage of red rock crab Cancer productus drawings of fifth zoeal stage of red rock crab Cancer productus
drawing of megalopal stage of Cancer productus
Research study 6

Studies on larval development of Cancer gracilis collected at Seal Beach, California show that the protozoeal and 5 zoeal stages each last about 7d (at 17oC). The megalopal stage lasts about 15d.  About 16% of the original hatchlings reach the 2nd juvenile stag (second moult) in this study.   Ally 1975 Crustaceana 28: 231. Photo of Cancer gracilis courtesy Dave Cowles, Walla Walla U

NOTE  because the protozoeal stage in other Cancer species lasts only a day or two, the author thinks that the 7-d duration noted here may not be normal

photograph of crab Cancer gracilis courtesy Dave Cowles, Walla Walla U drawing of first zoeal stage of crab Cancer gracilis drawings of fifth zoeal stage of crab Cancer gracilis
drawing of megalopal stage of crab Cancer gracilis
Research study 7

Laboratory culture of Cancer crabs collected around Humboldt County, California confirms the presence of a short-lived “prezoeal” stage in the 3 species examined, Metacarcinus magister, Cancer productus, and C. antennarias.  The focus of the study is on the last species and drawings of the 5th zoeal (4.4mm Length) and megalopal stages (4.8mm Length) are shown here. Roesijadi 1976 Crustaceana 31: 275. Photo courtesy Iain McGaw, U Nevada.

NOTE  an earlier publication o these and other California cancrid crabs includes comparative morphology of maxillae of M. magister, C. antennarius, and C. anthonyi with a key to differentiating their zoea larvae.  Mir 1961 Calif Fish Game 47 (1): 103.

photograph of crab Cancer antennarias courtesy Iain McGaw, U Nevada drawings of fifth larval stage of crab Cancer antennarias drawing of megalopal stage of crab Cancer antennarias
Research study 8

Laboratory culture of Cancer anthonyi in Mission Bay, California shows a prezoeal stage lasting just 2h at 20oC, and 5 zoeal and one megalopal stages that are similar to those of M. magister and C. productus.  In fact, so similar are these stages that the author says that there is no way to distinguish the 3 species in the field.  The author’s drawings of the 5th zoeal (4.2mm Length) and megalopal (3.2mm Length) stages are included here for comparison with those of the other species. Anderson 1978 Crustaceana 34: 55. Photo courtesy Dave Gardner, S. California

photograph of crab Cancer anthonyi courtesy Dave Gardner, S. California drawing of fifth zoeal larval stage of crab Cancer anthonyi drawing of megalopal stage of crab Cancer anthonyi
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Research study 9

histogram comparing spine lengths in first-stage zoea larvae of Dungeness crabs Cancer magister in Alaska and Californiadrawing of first-stage zoea larva of a crab Cancer magister indicating where morphometric measurements are taken in spine-length comparisonFirst-stage zoea larvae of Dungeness crabs Metacarcinus magister in Alaska have significantly longer dorsal, rostral, and lateral spines than comparable larvae in California by 14-29% (see drawing on Left showing measurements taken). By collecting in November and holding ovigerous females at temperatures of 5, 10, and15oC until the eggs hatch the authors determine that longer spines develop at lower temperatures (see histogram on Right). All spine lengths and body lengths of zoeae in Alaska are significantly longer that in zoeae from California.  In view of this the authors caution against strict use of spine lengths to distinguish between  larvae of the same species.  Shirley et al. 1987 Mar Biol 95: 371.

NOTE  hatching begins after 40-160d of culture depending upon temperature

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Research study 10

histogram comparing seasonality of egg-bearing in crabs Cancer antennarius and C. anthonyi in CaliforniaA study on crabs Cancer antennarius and C. anthonyi near Pt. Conception, California shows that females of the former species bear eggs mostly in winter/spring, while females of the latter species are ovigerous mainly in summer and autumn.  Reilly 1987 Cal Fish Game 73: 88.

Research study 11
  Laboratory culture of eggs from Cancer oregonensis and C. productus collected in Puget Sound, Washington reveals differences between these and California populations in the megalopa stage.  The authors provide a key for distinguishing megalopae in northern populations of the 2 species listed above as well as C. gracilis and M. magister.  DeBrosse et al. 1989.  Fish Bull 88: 39. Photos courtesy Ron Long, SFU (Cancer oregonensis) and Iain McGaw, U Nevada (C. productus).

NOTE  a later study by the senior author provides comparative data on 3 species of Cancer (the above 2 plus M. magister) collected from 3 sites within Puget Sound and 2 sites offshore (data not included here).  DeBrosse 1990 J Crust Biol 10: 315.

photograph of crab Cancer oregonensis courtesy Ron Long, SFU drawing of megalopal stage of crab Cancer oregonensis photograph of crab Cancer productus courtesy Iain McGaw, U Nevada drawing of megalopal stage of crab Cancer productus
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Research study 12

graph showing relationship between moult increment and size in Dungeness crabs Cancer magistergraph relating moulting frequency with size/age in Dungeness crabs Cancer magister in northern CaliforniaA detailed study of growth and reproductive dynamics is provided for adult female Metacarcinus magister in northern California.  Of 12,034 adults of 92-173mm carapace width tagged and released, 111 tagged moults are recovered.  Other observations are done on 166 individuals in the laboratory.  Chief findings are that moult increments decline with size/age from 21 to 12mm over the range of sizes noted above (see graph on Left). Furthermore, moulting frequencies decline from about 0.9 at sizes <135mm to near zero at 160mm (see graph on Right).   Most females extrude eggs annually, although some appear to do so without moulting and mating.  Sperm appears to be viable for up to 2.5yr.  Fecundity in large individuals can be up to 1.6 million eggs, depending not just on crab size but also on previous moulting history.  The authors provide much more useful information not included here.  Hankin et al. 1989 J du Conseil 46: 94.

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Research study 13

graph showing relationship between fecundity and size in 6 west-coast Cancer speciesA comprehensive study on reproductive output and fecundity for representatives of the genus Cancer and Metacarcinus includes 6 west-coast species.  As known graph comparing lifetime fecundities in 6 species of Cancer crabsfrom other studies, female body size is the principal determinant of reproductive output (see Left graph).  Mean fecundities range from 18,000 to 2,200,000 eggs per brood.  Most species produce 2 broods per year over an average reproductive span of 7yr.  Lifetime output scales isometrically with body size, reaching a maximum for large C. productus of over 22 million eggs (see Right graph). Hines 1991 Can J Fish Aquat Sci 48: 267.

NOTE  these are C. oregonensis, C. gracilis, C. antennarius, C. productus, C. anthonyi, and Metacarcinus magister. Several other cancroid species are included in the study but not shown in the graphs

Research study 14

map showing study sites for research on crabs Cancer magister in southeaster Alaskagraph showing gonadosomatic index for crabs Cancer magister in southeastern AlaskaDungeness crabs Metacarcinus magister are distributed from the Pribilof Islands, Alaska to Santa Barbara, California.  To answer the question of whether females in northern populations extrude eggs annually as they do in southern populations, researchers in Alaska hold animals for a year and monitor gonadosomatic indices monthly from March-October in males, and in egg-bearing and non-egg-bearing females. Results from some field animals are also provided, but not shown here.  The data indicate (see graph) that most non-ovigerous females resorb their gonads in the autumn, indicating that egg-extrusion is not an annual event for the majority of females in southeastern Alaska. The study is the first to document gonad resorption in Dungeness crabs. Swiney & Shirley 2001 J Crust Biol 21: 897; see also Swiney et al. 2003 J Crust Biol 23(2): 280.

NOTE  a measure of gonad mass to fresh body mass (after removal of gonads) x 100%, the same as "Gonad Index" used by researchers


What possibilities exist for the decrease in gonadosomatic index in non-ovigerous females?  Consider these answers then CLICK HERE for explanations.

Gonads are absorbed. 

Body mass increases. 

Eggs are extruded but not held by the female, perhaps because they are not fertilised. 

Research study 15

histogram showing duration of amplexus in crabs Cancer gracilis in Puget Sound, Washingtondrawing of reproductive parts of female crab Cancer gracilisCollections from several locations in Puget Sound, Washington provide details on the breeding biology of Cancer gracilis.  Individuals aggregate to breed in August.  Males are mature at 77mm carapace width (CW). While ones smaller than this may have spermatophores in their vas deferens, they are unresponsive to receptive females.  Females start mating at about 50mm CW, and are fully receptive and copulating at about 60mm.  Females may copulate more than once, so sperm competition is likely. Prior to copulation, which occurs after the female moults, the male carries the female upside-down under his body in amplexus for several days (see graph on Left). Copulation ensues after the female moults and it takes about an hour for intromission to start.  Intromission itself takes about 40min.  After copulation the male guards the female for a time by standing over her and forming a cage with his legs.  Later, when released, the female may copulate again.  During copulation the male’s gonopods cannot extend the full length of the vagina into the spermatheca, so movement of sperm is assisted by pumping contractions of the male's pleon, or lower body surface. 

The sperm deposit consists of a mass of spermatophores (sperm packets) which, when the male is finished, forms a membrane-bound body known as a sperm plug.  The plug has 3 parts: a head, shaft, and the main body of the plug within the spermatophore (see drawing on Right).  Note that the oviduct enters the spermatheca towards its ventral side (marked by a blue arrow), and this is the route followed by the eggs when they are released several days or weeks after copulation.  As they pass through the sperm-packed spermatheca the eggs are fertilised and then attached to the bristly pleopods as an egg mass (see photo of Hemigrapsus oregonensis as an example). photograph of grapsid crab Hemigrapsus oregonensis bering eggs cra

Note in the drawing the presence of an old sperm plug that is sometimes retained through the female’s moult.  Interestingly, in such a case the sperm plug from the most recent copulation pushes the old plug upwards and into the “cul-de-sac” of the spermatheca, out of contact with the oviducal opening.  This ensures that only the new sperm will fertilise the eggs.  In an instance of a double copulation in a single receptive period by a female, the plugs are deposited in the spermatheca side-by-side, presumably in no particular order relative to the oviducal opening; hence, which sperm do the fertilising is a matter of chance.  The authors note that “sperm competition” takes the form of post-copulatory mate guarding as well as sperm plugs.  Orensanz et al. 1995 J Zool Lond 235: 411.

NOTE  sperm plugs of C. gracilis are of the “external” type, that is, they protrude from the vagina.  Other species may have an “internal” type

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Research study 16

drawing of reproductive system in a female crab Cancer magisterA contribution from the same research group1 in Research Study 15 above on Cancer gracilis provides complementary information on functional morphology of the reproductive system in female Metacarcinus magister.  Spermathecae in M. magister are of the “ventral type”, that is, the vagina and oviduct open into the spermatheca in close proximity.  A new structure is described in M. magister, apparently unique for brachyurans, and that is the bursa (see drawing). The bursa often contains sperm and is located, and opens into, the distal end of the vagina near to where it leads to the gonopore sited on the 2nd walking leg.  The bursa is 5mm in diameter and has a capacity of about 100µl.  The vagina is about 2cm in length.  The sperm plug, a mechanism for preemption, that is, replacement or displacement, of stored sperm from a rival, is also unique in that it obstructs only half the length of the vagina and does not occlude the gonopore.  The plug is placed in the vagina by the first male to mate with a newly moulted female to prevent subsequent access by another male’s spermatophore.  The plug may be in the vagina between the bursa and the spermatheca or part way into the bursa, and it often extends partly out of the gonopore.  The plug appears not to prevent subsequent copulations, but the spermatophores from these later matings are diverted into the bursa.  The plug is in 2 parts.  In the vagina proper, the innermost section of the plug adheres to the walls and forms a tight seal.  In contrast, the  outermost section of the plug is more friable, does not adhere to the vaginal wall, and if it protrudes from the gonopore it usually falls off a short time after copulation.  The authors note that only about half the length of the male’s gonopod enters the vagina, its width stopping it at the vaginal constriction.  In a recently mated female the spermatophore contains free spermatophores, white in colour, that form a solid mass.  By the time of egg extrusion, several months after copulation, the spermatophore walls have disappeared, and the sperm are mostly free in the mass.  The eggs pass through this mass, are fertilised, released from the gonopore, and caught up in the bristles of the female’s pleopods.  Although the most obvious function for the bursa would seem to be for short-term2 sperm storage, the authors give several good reasons3 why this is unlikely and promise to investigate the matter further.  Jensen et al. 1996 Biol Bull 190: 336.

NOTE1  School of Fisheries, University of Washington, Seattle

NOTE2  long-term storage is unlikely because the inner lining of the bursa is lost during moulting

NOTE3  some examples are: sperm in the bursa may be exposed to seawater seep during copulation, sperm are often in a degenerative state, and there is no obvious path for oocytes to move through the bursa nor for sperm to be moved from the bursa to the vagina

Research study 17

map of Fritz Cove, Alaska showing study sites for research on movements of crabs Cancer magistermaps showing movements of female crabs Cancer magister in Fritz Cove, Alaska at different times of the year
Use of ultrasonic telemetry devices allows movements of Dungeness crabs Metacarcinus magister in Fritz Cove (near Juneau, Alaska) to be monitored over periods of 2-18mo. Males and females behave differently.  Females are inactive (generally buried in dense aggregations) at water depths below 20m between Nov-Apr, then move into shallow maps showing movements of male crabs Cancer magister in Fritz Cove, Alaska at different times of the yearwater (<8m) in late April where they release zoeae up to early June, and move back into deeper water in July. Moulting in females occurs in Jun-Jul, presumably accompanied by copulation. 

Movements of males parallels those of females, with migration from deep water in April to shallow areas (<25m), but staying segregated from females until July.  In autumn the males return to deeper water. Overall, females only range 1.5km from the mouth of Fritz Cove, while males move 7km from the head of the cove.  Stone & O’Clair 2001 Mar Ecol Progr Ser 214: 167.

NOTE  the devices operate ultrasonically, each with a unique code for individual identification.  They are glued to the upper carapace with quick-drying epoxy putty

NOTE the coloured dots in the figures above are meant for visual emphasis only; each dot does not represent a single crab. A crab that stays more or less in pne spot for several months will be represented by a single dot, whereas one that moves around a lot will be represented by several dots

Research study 18

A later study by the same authors on the behaviour of female Metacarcinus magister in Fritz Cove, Alaska reveals surprising home-site fidelity. To test homing behaviour the researchers attach ultrasonic telemetry devices to 8 ovigerous crabs and move them 1.4km from their brooding site.  A second control batch of 8 ovigerous crabs are similarly tagged and returned to their brooding site.  Locations of all tagged crabs are monitored weekly over an 8-mo period to determine activity patterns, and changes in depth and habitat usage, in additon to homing tendencies.  Within 13-20d, 7 of the 8 translocated crabs have returned to their original site.  The general pattern of behaviour of the female includes inactivity (usually buried) at depths greater than 16m during winter/early spring, a movement into shallower water during mid-April/June, and increased activity in July with movement back to deeper water, presumably to forage.  Movement into shallow water in springtime coincides with the spring phytoplankton bloom and hatching of the zoea larvae from the females. The authors conclude that much of the behavior of M. magister is related to the reproductive status of the females.  Stone & O’Clair 2002 J Crust Biol 22: 481.

Metacarcinus magister buried 0.6X

Research study 19

photographs of lower vaginal areas of Dungeness crab showing sperm plug in situAll fisheries that select the largest males for harvest run the risk of leaving a portion of reproductively mature females uninseminated.  This is investigated at 2 sites (Clam Beach and Big Lagoon) in northern California by researchers at Humboldt State University by collecting large, recently moulted, female Metacarcinus magister and examining them for presence and status of sperm plugs.  Results show photographs of crab vagina with sperm plugthat of 336 of the largest females collected (>140mm carapace width), over 98% have either complete, or remnants of, sperm plugs in their vaginal tracts (see illustrations showing location of sperm plugs in mated and unmated females).   From other laboratory observations the researchers know that sperm plugs will last for at least 180d after mating, a time exceeding the approximate 4mo duration of mating season for Dungeness crabs in northern California.  The authors conclude that despite an intense fishery on large male crabs in the area, their evidence from sperm plugs indicate essentially 100% mating success among large, recently moulted females.   Oh & Hankin 2004 J Crust Biol 24(2): 314; for more on the same subject see Hankin et al. 1997 Can J Fish Aquat Sci 54: 655.

NOTE  the overall collection actually totals 590 females of 87-167mm carapace width, of which 93% have either complete or remnants of sperm plugs.  The data cited above are for the very largest females in this overall collection


Details of reproductive tract of a recently mated
female crab Metacarcinus magister showing a sperm plug with
the tip extending into the spermatheca. Compare this
illustration with those in Research Studies 15 & 16 above

Research study 19.1

drawings of stage I zoea larva of crab Cancer antennariusResearchers at California State University, Fresno provide drawings and drawings of stage I zoea larvae of crab Cancer productusa dichotomous key for zoeal larval stages of crabs in San Francisco Bay.  The survey includes 13 species, of which Cancer productus and C. antennarius are shown here (stage I zoeae only; C. gracilis zoeae are identical to those of C. antennarius).  Rice & Tsukimura 2007 J Crust Biol 27 (1): 74.

NOTE  other genera Carcinus, Eriocheir, Fabia, Hemigrapsus (2 spp.), Lophopanopeus, Pachygrapsus, Pinnixa, Pyromaia, and Rithropanopeus can be found in their own sections in the ODYSSEY.  Separating them in this way is not so handy, but interested readers can use the links provided here to navigate from one to the other. The key requires too much detailed anatomy to be included here. Most species are described from the literature, but a few are cultured from gravid females 

Research study 20

graph showing seasonal abundances of larvae of Cancer oregonensis in AlaskaLight-trap collections of Cancer oregonensis larvae in kelp beds in  Kachemak Bay, Alaska by researchers from the University of Alaska reveal peaks in abundance in midsummer-early autumn (see graph).  A total of 10,016 zoeae and megalopae are collected over a 16mo period, of which C. oregonensis (60% of the total) and the mussel-crab Fabia subquadrata (32%) are the most abundant Daly & Konar 2008 Mar Biol 153: 1055.

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