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Dungeness crab (Cancer magister) fisheries of the eastern Pacific, from Alaska to central California, have a minimum size limit, measured as carapace width (CW), to ensure that all harvested males have had the opportunity to participate in at least one mating season as sublegal-sized crabs. Dependable indicators of female mating activity have been revealed, but mating activity of males has only been indirectly inferred through examination of  so-called "mating marks", presumably created  during the premating embrace between a male and female. Previous researchers found that mating marks were present on a higher percentage of sublegal-sized males than on legal-sized males, leading to implications that in a fished population large females may go unmated, and cause a reduction in overall egg production. I present results from laboratory experiments designed to discover the process of mating mark formation, along with at-sea observations documenting the occurrence of mating marks in a natural population in northern California. The experiments involved laboratory matings of male and female crabs to determine the factors that influence the formation of mating marks. Hypothetical factors that may affect mating mark formation include relative male and female sizes, mating frequency, competition, and substrate type. A total of 107 male crabs, some mated multiple times and in different conditions, were allowed to form a total of 155 premating embraces in the laboratory. No mating marks were produced in any of the controlled laboratory matings, however. Mate takeovers, when a competing male displaces the female mate of another male in a premating embrace, were observed, resulting in males forming premating embraces with each other. In addition, inter-male competitive behaviors were observed that may produce marks on the males' claws. At-sea observations revealed that as the mating season progressed, the frequency of mating mark occurrence on all male crabs increased. Throughout the 2004 mating season, sublegal crabs in northern California had a slightly higher frequency of mating marks than legal crabs on half of the collections while half of the collections yielded a slightly higher mating mark frequency on legal crabs. Reliable use of mating marks to indicate mating success would require that (1) every premating embrace, involving the smallest to largest male capable of mating, produces mating marks; (2) every premating embrace results in successful copulation and insemination; and (3) the timing and location of field samples are  appropriate for  estimating population-level mating activity. Data from laboratory matings and at-sea observations show that these assumptions cannot be reasonably accepted, and therefore it is misleading to use mating marks as an index of mating activity in male Dungeness crabs.

Identifying where and how larvae accumulate in space and time is key to understanding the dynamics of benthic marine populations and communities and for locating marine reserves, particularly in recruitment-limited upwelling regions. The interaction of alongshore coastal currents with large headlands has been shown to increase the accumulation of planktonic organisms through the formation of headland eddies. Larval settlement of benthic invertebrates and circulation around Bodega Head, a small headland in an upwelling region, was investigated to determine if similar processes are at work around both large and small headlands. During the upwelling seasons of 2000 through 2004, invertebrate settlement rates and physical variables, including wind, current, and water properties, were monitored to identify spatial and temporal settlement patterns, circulation features, and larval transport mechanisms. A larval accumulation zone was identified in the lee of the headland where crabs, mussels, and barnacles settled in greater abundance than along the exposed coast. Oceanographic sampling revealed a sub-surface recirculation feature in the lee of Bodega Head. This recirculation feature strengthened as upwelling increased providing a mechanism for larvae to accumulate in an area thought to have extensive offshore transport. During relaxation this recirculation feature weakened allowing the potential export of larvae to adjacent habitats. High frequency sampling revealed interspecific differences in larval transport mechanisms. Strongest correlations with physical variables that are indicative of upwelling and relaxation conditions were observed for Cancer magister, which settled primarily during relaxation-favorable conditions, and for Cancer antennarius/productus, which settled primarily during upwelling-favorable conditions. Further, C. magister and C. antennarius/productus settled at different depths and exhibited different spatial distributions, suggesting that these two congeners employ different strategies for returning to adult habitat. Non-cancrid crab settlement was correlated with tidal periodicity, indicating the importance of multiple taxon-specific delivery mechanisms. We suggest that both small and large headlands predictably accumulate larvae and are particularly effective during periods of strong upwelling. Thus larval accumulation zones should be included in networks of marine reserves in upwelling regions where advection of larvae may limit recruitment to adult populations.

Dungeness crab support a valuable commercial fishery in California, yet in recent decades the fishery has intensified significantly, with most crab landed during the first 6 weeks of the 7-month season. This study of fishermen’s operating costs and their opinions of new management measures is intended to support discussions and decision-making about policy changes that may affect the economics of the fishery. Our survey results show that a majority of fishermen have favorable views of only two of 12 alternative measures (one trap-limit for all size vessels and daylight-only fishing). However, opinions of these measures vary between owners of different-sized vessels. Experiences in other crustacean trap fisheries around the world suggest that simply implementing these two measures may not significantly decrease total trap numbers fished or slow the race for crab.

The complete mitochondrial (mt) genome of Cancer magister was obtained using next-generation sequencing. The circular genome was 39,658 bp in length, consisting of 13 protein-coding genes, 26 transfer RNA genes, and 2 ribosomal RNA genes. Unfortunately, the control region was not found in mitochondrial genome. Of the 41 genes, 24 were encoded by the heavy strand, while the others were encoded by the light strand. The genome composition with A + T bias (69.90%). The phylogenetic analysis showed that C. magister and Cancer pagurus was clustered together, then grouped with A. alayseae and Gandalfus puia, which may suggest Cancroidea was close with Bythograeidae. The newly described mitochondrial genome may provide valuable data for phylogenetic analysis for Cancridae.

The specific dynamic action (SDA) describes the postprandial increase in metabolism. It is a composite of mechanical and chemical digestion, nutrient transport and protein synthesis. How these individual events contribute to the overall SDA has not been worked out fully for any organism. The mechanical events associated with the SDA were investigated in Dungeness crabs, Cancer magister . Following consumption of a meal, oxygen consumption (MO 2 ) remained elevated for several hours. When the crabs were presented with fish scent there was a 2 fold increase in MO 2 , which rapidly decreased once the stimulus was removed. Crabs were then offered fish in a perforated tube. There was a rapid increase in MO 2 associated with handling which returned to pre-treatment levels within an hour of removal of the tube. Finally the crabs were fed a piece of foam that had been soaked in fish water to determine the costs of mechanical digestion. The mechanical breakdown of the meal accounted for 29.9 ± 3.3% of the overall SDA. Since food handling produced a large increase in MO 2 , it was reinvestigated using crabs that had one or both claws removed. Although there were no statistically significant differences as a function of claw removal there was a consistent trend in the data. The maximum MO 2 , scope, duration and SDA increased from animals with 0 claws through 1 claw to 2 claws. The results showed that the mechanical portion of the SDA can account for a significant portion of the overall budget in decapod crustaceans. [ABSTRACT FROM AUTHOR]

The mechanics and emergence patterns associated with burying behaviour were investigated in the Dungeness crab, Cancer magister, and the red rock crab, Cancer productus. Cancer magister used both the legs and chelae to excavate the sand, whereas Cancer productus used the legs to pull and push itself down into the sediment only using the chelae in a final push beneath the sediment. Several individuals of each species remained buried for over 50 h, which was accomplished by alterations in ventilatory physiology. More commonly, both species exhibited an endogenous rhythm of circadian periodicity, with peak periods of emergence from the sand occurring during nocturnal high tides. Although burial may act as a means of predator evasion and to ambush prey, it appears the primary reason may be to conserve energy. These two species of crabs often occur sympatrically; the difference in behaviours is closely related to previously reported differences in physiological mechanisms between the two species when buried.

Due to their habitat specificity, marine parasites present excellent systems for studying the processes and patterns of larval settlement. Settlement of Carcinonermertes errans, an egg predator of the Dungeness crab, is described here for the first time. Upon contact with a host individual , competent larvae of C. errans settled on the crab's exoskeleton and migrated under the abdominal flap within 24 h. When removed from the host, recently settled worms retained their larval characteristics. After 48 h on the host, however, metamorphosis proceeded and larvae became juvenile worms. Additional field studies showed that competent larvae were present in the waters of the Coos Bay Estuary during the months of August through early November, could infect crab hosts directly from the water column, and exhibited density-dependent gregarious settlement. [ABSTRACT FROM AUTHOR]

An increasing number of examples suggest that interactions among introduced species are ecologically important and relevant to the management of invaded systems. We investigated the potential for the introduced cephalaspidean sea slug Philine orientalis to interfere with the feeding of the introduced European green crab ( Carcinus maenas) and the native Dungeness crab ( Cancer magister). We observed co-occurrence of crab species and P. orientalis at field sites in Bodega Harbor and Tomales, San Pablo, and San Francisco Bays. In laboratory and field experiments, we determined whether crab feeding was suppressed by P. orientalis and the duration of this suppression for individual crabs. We also used foraging response models to explore changes in the feeding rate of crabs with varying densities of P. orientalis and small bivalve prey. We found that P. orientalis deterred predation by green and Dungeness crabs on small clams in laboratory feeding trials, but not in field experiments with green crabs and P. orientalis. Foraging models predicted that P. orientalis would only affect crab feeding in the field under specific conditions of crab, P. orientalis, and prey densities. These foraging models bridged an important gap between lab and field experiments and allowed us to predict how changes in species abundances at two trophic levels might alter the importance of crab suppression by P. orientalis. [ABSTRACT FROM AUTHOR]

Abstract: Parasites can significantly impact ecosystems by altering the distributions and population sizes of their host organisms. Some hosts are thought to find refuge from parasitism by entering habitats where their parasites cannot survive. The nemertean worm Carcinonemertes errans is an egg predator that infects the Dungeness crab, Cancer magister, throughout the host's range. To determine if C. magister experiences a refuge from C. errans within estuarine environments, we examined the distribution of C. errans on Dungeness crabs within Oregon's Coos Bay Estuary. Year-round sampling over a three-year period also allowed us to test for temporal variation in the parasite's distribution. We found that parasite prevalence, mean intensity, and parasite density of C. errans infecting C. magister varied along a clear estuarine gradient, with crabs nearest the ocean carrying the heaviest parasite loads. Larger crabs were more heavily infected with worms, and seasonal infection patterns were observed at some sites within the bay. Crabs sampled from coastal waters near the estuary carried significantly more worms than did crabs from the bay, suggesting that the estuary is acting as a spatiotemporal parasite refuge for this important fishery species. [Copyright &y& Elsevier]

A typical nemertean pilidium larva resembles a hat with ear flaps. But one type, called pilidium recurvatum, looks more like a sock, swimming heel first. This distinctive larva was discovered in 1883 off the coast of Rhode Island and subsequently found in plankton samples from other parts of the world. Despite the long time since discovery, and its significance in discussions of larval evolution, this larva remained unidentified even to the family level. We collected pilidium recurvatum larvae from plankton samples in Coos Bay, OR, and identified them as belonging to the heteronemertean genus Riserius based on juvenile morphology and DNA sequence data. Phylogenetic analysis suggests that two distinct types of pilidium recurvatum from Oregon represent two new species within this currently monotypic genus. We describe the morphology of pilidium recurvatum using confocal microscopy and compare it to that of the typical pilidium, discussing possible implications for larval feeding. We also report our surprising discovery that juveniles of Riserius sp. from Oregon prey on another nemertean, Carcinonemertes errans, an egg predator of Cancer magister (Dungeness crab) , a commercially important species. We speculate that the species-level diversity and geographic distribution of Riserius may be much greater than currently appreciated. [ABSTRACT FROM AUTHOR]

For 12 yr (1997-2001, 2006-2012) daily abundance of Cancer magister megalopae was measured in Coos Bay, Oregon. Before 2007 from 2000 to 80 000 megalopae were caught annually. In 2007, catch jumped and has since varied from 164 000 to 2.3 million. The step change in catch size appears related to a shift to negative Pacific Decadal Oscillation ( PDO) values. Late season catches, which cannot be due to local spawning, are negatively correlated to the PDO, suggesting that these megalopae derive from north of the California Current. During periods of lower and higher catches, annual returns of megalopae were significantly negatively correlated to the day of the year of the spring transition and positively correlated to the amount of upwelling during the settlement season. The size of the Oregon commercial catch lagged 4 yr to allow for growth of recruits into the fishery is set by the number of returning megalopae; the relationship is parabolic. At lower returns, the population is recruitment limited, but at higher returns, density-dependent effects predominate and set the commercial catch. Lagged commercial catches in Washington and Northern and Central California were also related to the number of megalopae returning to Coos Bay, suggesting that the forces causing variation in larval success are coast wide. If high return rates are due to a PDO regime shift, then for years to decades the commercial catch may be set by density-dependent effects following settlement and the huge numbers of returning megalopae may impact benthic community structure. [ABSTRACT FROM AUTHOR]

Abstract: The Dungeness crab, Cancer magister, is a commercially important crustacean that ranges from the Pribilof Islands, Alaska, to Santa Barbara, California. Mating occurs between recently moulted females and post-moult males. After approximately 90 days, females release planktonic larvae into the water column. Stage-I zoea are found in the nearshore environment and subsequent zoeal stages are found at greater distances. After approximately 80 days, zoea moult into megalopa, which move first from the open ocean onto the continental shelf and then across the shelf to settle in the nearshore environment or estuaries. Crabs reach sexual maturity at 2–3 years of age. The fishery for C. magister is managed using a 3-S management strategy which regulates catch based on size, sex and season. As more fisheries seek sustainability certifications, the Dungeness crab fishery presents an excellent test case of how to sustainably manage a crustacean fishery. [Copyright &y& Elsevier]

Abstract: Combined field and laboratory experiments were carried out to investigate the salinity and thermal preference of adult Dungeness crabs, Cancer magister (Dana). In the field, crabs were fitted with archival CTD data tags to monitor the salinity, temperature and depth experienced at 10min intervals. Crabs spent the majority of time in conditions that did not present a physiological challenge and at depths below 15m. However, all crabs that were at large for more than a week made migrations to depths shallower than 15m. Exposure to stressful salinity and temperature conditions in shallow water (<15m) showed a distinct pattern and could be divided into short exposure times (<20min) associated with movements to deeper water which were indicative of avoidance behaviour, and longer exposure periods that suggest animals were actively foraging in the shallows of the estuary. Results obtained from laboratory preference experiments using salinity (16 to 32) and temperature gradients (8 to 22°C) confirmed data from tagged crabs in the field. Overall, crabs showed a strong avoidance of low salinity. However, when crabs that had been starved for 21d were presented with a food stimulus in low salinity, they showed directed movements towards the stimulus and spent more time in low salinity. Likewise, when presented with a food stimulus in high temperatures, starved crabs spent more time searching for food in high temperature than those which had recently fed. The results of this study suggest that crabs are primarily exploiting estuarine habitats under optimal environmental conditions, but that exposure to deleterious salinities or temperatures may be altered by the presence of food. [Copyright &y& Elsevier]

The article presents a study on the effect of ecological alterations of the bioengineering macrophyte Atlantic smooth cordgrass to the foraging habitat of the native predator Dungeness crab. The study utilized trapping surveys of crab habitats in Willapa Bay, Washington with passive sampling method to observe the foraging behaviors of crabs. Results of the study indicate that Atlantic smooth cordgrass limits the access of Dungeness crabs to prey resources and increases the rates of stranding.

Abstract: Aquatic organisms routinely experience fluctuations in oxygen levels. In response to oxygen deprivation, many organisms increase the oxygen carrying capacity of their blood to restore balance to hypoxic cells and tissues. This response has been well described in vertebrate as well as invertebrate systems. The respiratory pigment found in decapod crustaceans, hemocyanin (Hc), increases in concentration and is differentially regulated in response to decreases in oxygen tension. To test the effects of hypoxia on Hc regulation in Cancer magister, adult crabs were exposed to hypoxic conditions (6.4kPa) for 12days. Total protein and oxyhemocyanin were significantly higher in crabs that had been exposed to hypoxic conditions. Hemocyanin analyzed by pH7.4 PAGE showed that the concentration of both the 16S and 25S conformations of Hc significantly increased in hypoxic crabs. We also show that C. magister differentially regulates Hc subunits 3 and 6 when challenged by hypoxia. As Hypoxia-Inducible Factor-1 (HIF-1) is considered to be the global regulator for oxygen homeostasis, we have also identified putative HIF-1α binding sites in the promoter and intronic sequence of several Hc subunits. The presence of these potential hypoxia response elements, the conservation of physiological responses, and the discovery of a HIF-1α homologue in C. magister and several other crustacean species, suggest a role for HIF-1 in regulating crustacean responses to hypoxia. [Copyright &y& Elsevier]

Decapod crustaceans are well known for agonistic interactions where they commonly fight over resources. Accurate descriptions of crab behaviour are essential to the development of quantitative behavioural studies involving the Dungeness crab fishery. An underwater video system mounted over a commercial crab trap in situ was used to qualitatively describe several of the most common behaviours utilized by Cancer magister in and around traps, including the documentation of previously undescribed behaviours in this species. Crabs commonly guarded trap doors without entering the trap and prevented other inspecting crabs from entering the trap. Agonistic interactions in traps ceased when crabs 'clustered' together, creating a group of non-interacting, fairly motionless crabs sitting on or near each other. These observations indicate that crab behaviour merits further attention in future studies of gear saturation and the catchability of Dungeness crabs. [ABSTRACT FROM AUTHOR]

This study presents a methodology for combining archival data storage tags (DSTs) and ultrasonic transmitters to investigate the microhabitat conditions of adult Cancer magister (Dana), inhabiting an estuary. The temperature, salinity and depth experienced by free-ranging Dungeness crabs were recorded at 10-min intervals for periods ranging from 1 week to 8 months. Crabs were tracked using a hydrophone, and tags were recovered via concentrated trapping or returned by recreational fishers for a reward. These methods led to a return rate of 50%. Representative CTD tag data showed that the conditions recorded at fixed stations within the estuary were not reflective of those experienced by free-ranging crabs, but rather crabs were able to orientate and avoid low salinity within the estuary. The prevalence of low salinity exposure was linked to times of increased food availability within the estuary, suggesting that crabs were entering the shallows of the estuary to forage. The techniques used in this study demonstrate that DSTs are a viable means of determining the microhabitat conditions of crustaceans inhabiting highly variable environments. [ABSTRACT FROM AUTHOR]

Ecologists have long debated the relative importance of biotic interactions vs. abiotic forces on the population dynamics of both marine and terrestrial organisms. Investigation of stock size in Dungeness crab (Cancer magister) is a classic example of this debate. We first tested the hypothesis that adult population size was set by larval success. We, found that during a five-year sampling period, adult crab population size from Oregon through central California, USA, as measured by the commercial catch, varied directly with the number of terminal-stage larvae (megalopae) returning to Coos Bay, Oregon, four years earlier; adult population size was largely determined (>90% of the variation) by success during the larval stage. We then tested whether biotic interactions or abiotic forces caused the variation in larval success. Most of the variation (>90%) in the number of returning megalopae is explained by the timing of the spring transition, a seasonal shift in atmospheric forcing that drives ocean currents along the west coast of the United States. Early spring transitions lead to larger numbers of returning Dungeness megalopae, while in four other crab taxa, species with very different life history characteristics, early-spring transitions lead to lower numbers of returning megalopae. During the past roughly 30 years, the size of the commercial catch of Dungeness crab is significantly and negatively correlated with the date of the spring transition throughout the California Current system. Long-term variation in the date of the spring transition may explain a major crash in the Dungeness crab fishery in central California, which began in the late 1950s. The data suggest that Dungeness crab population size is determined by variation in larval success and that a significant portion of this variation is due to the timing of the spring transition, a large-scale climatic forcer. [ABSTRACT FROM AUTHOR]

Barber J. S., and Cobb, J. S. 2007. Injury in trapped Dungeness crabs (Cancer magister). – ICES Journal of Marine Science, 64: 464–472. Although traps are the most effective fishing equipment used to capture crabs they can also result in indirect damage to target species. We examined the effect of trap-soak time, crab density, and the legal to sublegal size ratio on injury rates to male Dungeness crabs, Cancer magister. Our field results show that injuries increase significantly with increased trap-soak time, and as a consequence of different size ratios (crabs in traps with a greater ratio of sublegal crabs had more injuries). The injury rate was independent of density. In a laboratory experiment, injured crabs were as capable as intact crabs of obtaining, defending, and consuming food. However, studies on other crab species indicate that injury reduces growth, delays reproduction, decreases mating success, and increases mortality. If the costs of injury are similar for Dungeness crabs, this could diminish the rate of recruitment into the fishery. [ABSTRACT FROM PUBLISHER]

Hemocyanin, the blue blood protein of many arthropods and molluscs, reversibly binds oxygen at its highly conserved copper-oxygen-binding sites and supplies tissues with oxygen. Cryptocyanin, closely related structurally and phylogenetically to arthropod hemocyanin, lacks several of the six critical copper-binding histidines, however, and has lost the ability to bind oxygen. Despite this loss of function, cryptocyanin continues to be synthesized, an indication that it has been exploited to carry out new functions. Here, we show that cryptocyanin is present in extremely high concentrations in the hemolymph of the crab during the premolt portion of the molt cycle. Both proteins are specifically expressed in the same type of cell in the hepatopancreas and secreted into the hemolymph, but cryptocyanin plays a major role in forming the new exoskeleton, while hemocyanin functions in oxygen transport. A cessation in cryptocyanin, but not hemocyanin, synthesis after eyestalk ablation supports our hypothesis that cryptocyanin is closely regulated by molting hormones. The contrasts between the two gene products illustrate how a gene duplication of a copper-oxygen protein and its subsequent mutation may work in concert with the evolution of new regulatory mechanisms, leading to the assumption of new functions. [ABSTRACT FROM AUTHOR]

Decapod crustaceans inhabit aquatic environments that are frequently subjected to changes in oxygen content. The physiological mechanisms that allow them to cope with periodic episodes of hypoxia have been well documented. Most crustaceans exhibit a bradycardia coupled with diversion of haemolymph from digestive organs towards ventral structures. However, all these experiments were conducted on animals that were starved prior to experimentation in order to avoid increases in metabolism associated with digestive processes. The present study sought to determine how the Dungeness crab Cancer magister balances the demands of physiological systems when they feed and digest in hypoxia. Cardiac parameters and haemolymph flow rates through each arterial system exiting the heart were measured using a pulsed-Doppler flowmeter. Scaphognathite beat frequency (ventilation rate) was calculated by recording changes in pressure in the branchial chamber. There was an increase in both cardiac and ventilatory parameters following feeding. Digestive processes were facilitated by an increase in haemolymph flow rates through the anterior aorta, hepatic arteries and sternal artery. Cancer magister showed a typical bradycardia during hypoxia (3.2 kPa). However, food intake caused a significant reduction in this response. Likewise, ventilation rate also showed effects of addivity, increasing in response to both food intake and hypoxia. Digestion during hypoxia was associated with a decrease in both stroke volume and cardiac output. Blood was diverted away from digestive structures, suggesting that blood flow events are prioritized during hypoxia. The changes in haemolymph flow rates paralleled those in previous reports on reductions in protein synthesis in the hepatopancreas during hypoxia. Haemolymph flow rates through the anterior aorta did not change; thus the blood supply to the supraoesophageal ganglion was maintained during feeding in hypoxia. The results show that the nutritional state of an animal is important in modulating its physiological responses to environmental perturbations. This underscores the importance of an integrative approach, studying physiological responses at the organismal level. [ABSTRACT FROM AUTHOR]

Coastal peoples worldwide harvested and consumed a wide variety of shellfish. Most archaeological analyses of shellfish remains tend to focus on bivalves such as clams and mussels while other shellfish such as gastropods, barnacles, and crabs have received much less attention. Here we examine the use of Dungeness crabs (Cancer magister) at a late-Holocene village on Netarts Bay, northern Oregon Coast. Ethnographic and ethnohistoric records suggest that crabs were both individually hunted as well as gathered, often en masse. We employ allometric scaling of Dungeness claws (propal fingers) recovered from several household middens to estimate crab body size and age. These data indicate that while a wide age range of crabs were collected, most harvesting efforts focused on juveniles and young adults. This suggests that most Dungeness crabs at the site were gathered (not individually hunted) in Netarts Bay, most likely in shallow subtidal areas where cockles (Clinocardium nuttalli) were also being regularly taken. As such, Dungeness crabs were part of a foraging strategy that involved the efficient mass harvest of small prey using minimal technology. [Copyright &y& Elsevier]

Physiological parameters associated with burying were investigated in the Dungeness crab, Cancer magister, and the red rock crab, Cancer productus. Ventilation frequency of the branchial chambers increased while the crabs were burying, this was associated with the greater oxygen demand of the tissues. The number of ventilatory reversals in C. magister increased in number as well as in duration and magnitude when the crabs were buried, which functioned to clear the branchial chambers of sediment. In contrast, the number of ventilatory reversals in C. productus decreased. On the surface of the sand, cardiac parameters (heart rate, stroke volume, cardiac output) of both species remained stable. During the burial process, there was a large increase in cardiac output which was afforded primarily by an increased stroke volume of the heart. Once buried, cardiac output declined in both species; this was due to a decrease in stroke volume in C. productus, but a decreased heart rate in C. magister. There were also differences in haemolymph flows through each arterial system. During the burying process, both species increased haemolymph flow to the muscles of the limbs via the sternal artery. Once buried haemolymph flows to the limbs decreased, and increased flow to eyestalks and antennae via the anterior aorta occurred. Perfusion of the digestive organs via the anterolateral and hepatic arteries did not change when the crabs were buried. There was an increase in flow through the posterior aorta, of C. magister, but flow through this artery did not change in C. productus. Periods of spontaneous cardiac arrest were observed in both species while resting on the surface. These increased in duration in C. productus when buried, but there was no change in C. magister. Changes in ventilatory and cardiac variables were closely linked on the surface, but tended to uncouple when the animals were buried. The physiological responses of C. magister resembled those of true sand-dwelling crabs, whereas the responses of C. productus paralleled those of crabs that only bury occasionally in the substrate. Although these two species often occur sympatrically, they employ different physiological mechanisms when buried in the sediment. [Copyright &y& Elsevier]

The isolation, PCR amplification, and descriptive statistics of six microsatellite loci are described for the Dungeness crab, Cancer magister. Also reported is the inheritance of these loci in two families obtained from artificial crosses in the laboratory. All six loci conform to expectations under Mendelian inheritance and there is no evidence for linkage between any of the loci. Allelic size ranges for three of the loci are relatively large, ranging from 135–357 bp between the smallest and largest allele detected at that locus. At two of these loci upper allelic drop out (non-amplification of the larger allele in a heterozygous individual) can be problematic for scoring. Results from cross-species amplification in nine congeners are summarized. These loci will be valuable in studies requiring high-resolution genetic markers in Dungeness crabs and related species. [ABSTRACT FROM AUTHOR]

An aluminum smelter situated at the head of Kitimat Arm (BC, Canada) has discharged polycyclic aromatic hydrocarbons (PAHs) into the receiving waters since 1954. The purpose of the present study was to examine the distribution of PAHs contaminants in dungeness crabs (Cancer magister) collected in Kitimat Armand Douglas Channel (BC, Canada) by determining the concentrations of PAHs in the hepatopancreas and muscle tissues of crabs by using gas chromatography--mass spectrometry. Crabs were collected at specific sites down the Arm from the smelter on four separate occasions over a three-year period. Hepatopancreas and muscle tissues of the crabs were analyzed for 10 of the 16 PAH priority pollutants recommended by the U.S. Environmental Protection Agency. Results of the studies showed that the crabs had detectable levels of PAHs in hepatopancreas and muscle tissues. The highest concentrations of PAHs in the tissues were found at a site near the aluminum smelter, the alleged point source of PAH discharge. The concentrations of PAH analytes were high in crabs collected close to the smelter and at lower levels in crabs collected throughout Douglas Channel. These results show that PAHs discharged by the smelter were bioavailable to the crabs. The concentration of each PAH analyte in the hepatopancreas was found to be strongly related to its water solubility. However, the PAH analyte concentrations in the hepatopancreas and muscle did not appear to correlate highly with each other. [ABSTRACT FROM AUTHOR]

Adult female Dungeness crabs (Cancer magister) can be inseminated only while in a soft-shell condition immediately after molting. Population modelers have therefore assumed that all adult female Dungeness crabs undergo an annual molt. Based on this assumption, a tag-recovery project was initiated in northern California to determine demographic statistics of the adult female stock. Of 12,037 adult female crabs tagged and released, recoveries of 492 crabs in the commercial fishery showed that a large proportion of adult female Dungeness crabs fail to molt annually and that extrusion of viable eggs does not require annual molting and mating.A size-specific annual molting probability estimator was developed which accounts for commercial gear selection biases. Estimates using this technique showed that annual molting probabilities decline with increasing adult female size and become zero above 155 mm. Therefore, size and age are weakly correlated. Size-related population statistics are probably more meaningful than age-related statistics becapse molt increments and molting probabilities appear to be more dependent on size than age.Width frequency distribution separation failed to allow year class strength extraction and size­ specific survival rate estimation.      However, comparisons of width frequency histograms across years show variation in year class strength.Tag-recoveries provided an annual survival rate estimate of 0.2 for crabs fully vulnerable to the commercial gear (> 155 mm). Truncation of width frequency distributions over larger female sizes suggests that survival rates for smaller female crabs are greater. The extremely low survival rate and the cessation of molting for large adult females imply that adult female Dungeness crabs may become senescent after reaching a terminal size.

A gastric peptide from the Dungeness crab ( Cancer magister), extracted and characterized previously (Larson and Vigna 1983b), was localized in the foregut (stomach) of this species by immunocytochemistry using antisera specific for the bioactive carboxy-terminal amino acid sequence common to gastrins and cholecystokinins (CCKs). Immunoreactivity was found in all gastric epithelial cells and in the procuticle. Electron microscopy revealed an absence of peptidergic secretory granules in the gastric epithelial cells. The pattern of immunostaining suggests that the gastric epithelial cells secrete this peptide apically where it is incorporated into the cuticle lining the lumen. Specific immunostaining could not be demonstrated in various neural ganglia or in the hypodermis. The distribution of this peptide is different from that of gastrin/CCK in vertebrates and other invertebrates. This suggests that the crab gastric peptide is sufficiently similar to gastrin/CCK to react with C-terminal specific antisera, but may be anatomically, functionally, and possibly phylogenetically otherwise unrelated. [ABSTRACT FROM AUTHOR]