Ventilatory and cardiovascular modulation associated with burying behaviour in two sympatric crab species, Cancer magister and Cancer productus

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.     

Observations on the histopathology of a systemic ciliate (Paranophrys sp.?) disease in the Dungeness crab, Cancer magister

Infections of the hemolymph of crabs by ciliates have been known for almost a century. Originally placed in the genus Anophrys, these crab-parasitizing ciliates have been recently transferred to the genus Paranophrys. Infections were long thought to be confined to the hemolymph in living crabs, with death caused by consumption of all hemocytes. Histological examination of heavily infected, but living, Dungeness crabs demonstrate that the ciliates actively invade and probably consume many tissues of the host prior to death rather than saprophytically feeding on the decomposing tissues subsequent to death as previously reported.     

Hemocyte classification and differential counts in the dungeness crab, Cancer magister

The primary purposes of this research were to describe and classify the circulating hemocytes of Cancer magister and devise a method for making differential hemocyte counts for crustaceans. C. magister hemocytes were classified using two simple criteria: the presence or absence of cytoplasmic granules and staining characteristics of the granules, if present. Hyalinocytes (HC) were devoid of granules, intermediate granulocytes (IG) contained basophilic granules or a mixture of basophilic and acidophilic granules, and eosinophilic granulocytes (EG) contained large, acidophilic granules. Hemocyte renewal and a hypothetical maturation sequence of C. magister hemocytes are described and discussed. Differential counts revealed that granulocytes were more abundant than hyalinocytes. For 22 crabs, the mean percentage (and range) of each hemocyte class was: IG, 65.97 (57.50–73.80); EG, 17.76 (4.70–26.47); and HC, 16.25 (3.40–34.67). After additional data are collected and analyzed, the routine use of differential counts may prove to be a valuable method for monitoring the status and health of C. magister and perhaps other crustaceans as well.     

Uptake of Bacteriophage and Their Subsequent Survival in Edible West Coast Crabs After Processing

Edible West Coast crabs (Cancer magister and Cancer antennarius), when in seawater contaminated with coliphage T4, were found to accumulate high titers of this virus. To study the extent of the hazard presented by crabs contaminated with virus, samples of edible crabs were contaminated with coliphage T4 and then processed by boiling. Results indicated that virus in crabs withstood this method of processing. The survival rate varied from 2.5 to 20%, depending upon the processing time. Heat penetration studies showed that, although internal temperature in the crabs was sufficient to inactivate virus, the processing times normally used to cook crabs were not. These results suggest that processed crabs could serve as vectors for the dissemination of virus diseases if the crabs are harvested from a polluted area.     

Gastric processing in the Dungeness crab, Cancer magister, during hypoxia

The gastric physiology of the Dungeness crab, Cancer magister, was investigated over a range of oxygen tensions. Postprandial crabs reacted differently to hypoxia compared with unfed animals. The bradycardic response in postprandial animals was reduced, suggesting a summation of responses with feeding. A similar pattern was observed for ventilation rate. In unfed animals ventilation rate increased slightly as oxygen levels declined, but dropped significantly in oxygen tensions below 3.2 kPa, whereas in postprandial crabs it increased significantly in the lower oxygen regimes. Gastric processing of the meal was followed using a fluoroscope. Pyloric contraction rates were maintained during mild hypoxia, but decreased in 5.3 kPa oxygen tension and below. This led to an increase in clearance times of digesta from the foregut, midgut and hindgut regions. The slowing of gastric processing in the lower oxygen tensions suggested that the animals were unable to maintain their internal oxygen concentration. A significant reduction in efficiency of assimilation only occurred in the lowest oxygen regime tested (1.6 kPa). The range of hypoxia where gastric processing was affected corresponded closely to the levels of oxygen that modulate the foraging behaviour of C. magister. By using both physiological and behavioural mechanisms C. magister can maintain digestive processes, even in severely oxygen depleted environments.     

A systemic microbial disease in the Dungeness crab,Cancer magister,caused by a Chlamydia-like organism

A Chlamydia-like agent was diagnosed in Dungeness crabs, Cancer magister, collected from Willapa Bay and northern Puget Sound, Washington. Over a 5-year period, infected crabs were found during the months of December through March. Infection by the organism is systemic, resulting in greatly hypertrophied cells with appressed nuclei. Unlike Chlamydia or other Chlamydia-like organisms, the present microbe has a great affinity for connective tissue or connective tissue cells rather than epithelial cells. Transmission electron microscopy revealed the presence of several developmental stages that are similar to chlamydial stages, in addition to what appear to be slightly altered or aberrant stages.     

Host specificity of <Emphasis Type="Italic">Sacculina carcini</Emphasis>, a potential biological control agent of the introduced European green crab Carcinus maenas in California

The European green crab, Carcinus maenas, is an introduced marine predator established on the west coast of North America. We conducted laboratory experiments on the host specificity of a natural enemy of the green crab, the parasitic barnacle Sacculina carcini, to provide information on the safety of its use as a possible biological control agent. Four species of non-target, native California crabs (Hemigrapsus oregonensis, H. nudus, Pachygrapsus crassipes and Cancer magister) were exposed to infective larvae of S. carcini. Settlement by S. carcini on the four native species ranged from 33 to 53%, compared to 79% for green crabs. Overall, cyprid larvae tended to settle in higher numbers on individual green crabs than on either C. magister or H. oregonensis. However, for C. magister this difference was significant for soft-shelled, but not hard-shelled individuals. Up to 29% of the native crabs arrested early infections by melanizing the rootlets of the parasite. Most native and green crabs settled on by S. carcini became infected, especially when settled on by >3 cyprids. Infected green crabs died at more than twice the rate of uninfected green crabs. In contrast to green crabs, all infected native crabs died without producing an externa (reproductive sac). At high settlement intensities, infected native crabs frequently exhibited neurological symptoms (twitching, loss of movement) before death. These results indicate that use of S. carcini as a biological control agent could result in the death of native crabs. The magnitude of this effect would be proportional to the density of infected green crabs in the environment and the probability that cyprids would contact native crabs in the wild. Potential benefits of biological control should be assessed in relation to these potential non-target effects.     

Endogenous rhythms of haemolymph flow and cardiac performance in the crab Cancer magister

Heart rate and arterial haemolymph flow rates were measured in freshly trapped Dungeness crabs, Cancer magister, using a pulsed-Doppler flowmeter. In the laboratory, freshly collected subtidal crabs exhibited endogenous rhythms in both cardiac function and haemolymph flow through one or more arterial systems, of both tidal and diurnal periodicity. The strongest tidal rhythms were recorded in the sternal and paired anterolateral arteries. These endogenous rhythms of selective tissue perfusion are related to an underlying locomotor activity, but may also be involved with hormonal transport or feeding. Changes in both heart rate and stroke volume were responsible for the increases in haemolymph flow rates. These rhythms were not entrained by aerial exposure, since confinement of arhythmic crabs in intertidal cages did not re-entrain an endogenous tidal rhythm. Endogenous locomotory rhythms are known to be controlled by neurohormones released in cycles from the sinus gland on the eyestalk. These hormones may also control the endogenous cardiovascular rhythms, since these were abolished after eyestalk ablation in freshly collected Cancer magister. These results suggest that hormones synthesized and released by the X-organ/sinus gland complex may, together with pericardial hormones, play a role in modulation of crustacean cardiovascular function.     

Selective crab predation on native and introduced bivalves in British Columbia

Experiments were conducted to determine whether locally abundant crab species prefer co-occurring littleneck clams, Protothaca staminea (Conrad, 1837) and Tapes philippinarum (A. Adams and Reeve, 1850), relative to a recently introduced species, the varnish clam, Nuttallia obscurata, (Reeve, 1857). Prey preference, handling time, pick-up success, profitability and consumption rates were investigated for two crab species, Dungeness crab, Cancer magister (Dana, 1852) and red rock crab, Cancer productus (Randall, 1839) crabs. Both crab species preferred varnish clams over the native species. This may be attributable to the lower handling time, higher pick-up success and increased profitability of consuming varnish clams. Handling time appeared to be a factor not only in species preference, but also in the degree of preference, with shorter handling times corresponding to stronger preference values. Both native and introduced bivalves burrow into the substratum, with the varnish clam burrowing deepest. When feeding on clams in limited substratum both crab species preferred the varnish clam. In the unlimited substratum trials Dungeness crabs preferred varnish clams (although to a lesser degree) while red rock crabs preferred littleneck clams. This was likely due to the significantly deeper burial of the varnish clam, making it less accessible. Although the morphology (i.e. thin shell, compressed shape) of the invader increases its vulnerability to predation, burial depth provides a predation refuge. These results demonstrate how interactions between native predators and the physical characteristics and behaviour of the invader can be instrumental in influencing the success of an invasive species.     

Substrate–inhibitor specificity of cholinesterase and monoamine oxydase from optic ganglia of the pacific squid <Emphasis Type="Italic">Todarodes pacificus</Emphasis> and commander squid <Emphasis Type="Italic">Berryteuthis magister</Emphasis>

A comparative analysis of enzymological characteristics of cholinesterase (ChE) and monoamine oxydase (MAO) from the optic ganglia was performed in the Pacific squid Todarodes pacificus and Commander squid Berryteuthis magister caught in their four habitats across the Pacific Northwest. A substrate–inhibitor analysis revealed a homogeneity of T. pacificus and B. magister ChE preparations as well as homogeneity of T. pacificus vs. heterogeneity of B. magister MAO preparations. In case of thiocholine derivatives, the rate of hydrolysis induced by T. pacificus ChE was practically independent of the structure of the acyl group, whereas in case of B. magister ChE it was found to decrease in this substrate series. It is only T. pacificus MAO that was found to be able to deaminate also a diaminooxydase substrate histamine. ChE activity was higher in T. pacificus than in B. magister for the whole substrate series, while for MAO the same activity pattern was observed for tyramine, tryptamine and serotonin. In both squids, the sensitivity of ChE to organophosphorus inhibitors containing the dimethylbutyl group was by several orders of magnitude higher than that in mammals. The sensitivity of ChE to the siloxane reversible inhibitors was lower in T. pacificus ChE and much lower in B. magister than in mammals.     

Comparative-enzymological study of cholinesterases from optic ganglia of the Commander squid Berryteuthis magister individuals inhabiting different zones of the species area

In this review a comparative analysis is performed of enzymological characteristics of cholinesterase (ChE) from optic ganglia of individuals of the Commander squid Berryteuthis magister caught in 8 zones of its habitation area in the northern-western Pacific aquatorium, of ChE of the Pacific squid Todarodes pacificus as well as of the “standard” acetylcholinesterase from human erythrocytes and butyrylcholinesterase from horse blood serum. By the method of the substrate-inhibitor analysis there was shown homogeneity of ChE preparations from the B. magister individuals from different habitation zones. Kinetic parameters of the enzymatic hydrolysis of 8 ester substrates are presented as well as the data on study of identity of ChE properties in the B. magister individuals from different habitation zones. Study of the process of the ChE reversible inhibition from the Commander squid individuals under action of 57 mono- and bisonium inhibitors has revealed differences in ChE properties in squid individuals from isolates in different zones of the habitation area, which argues in favor of the existence of intraspecies groups of the Commander squid B. magister.     

Chemically induced predator avoidance behaviour in the burrowing bivalve Macoma balthica

The responses of the burrowing bivalves Macoma balthica and Cerastoderma edule to chemical cues emitted by feeding shore crabs Carcinus maenas were investigated. M. balthica held in the laboratory and exposed to chemical signals in effluent water discharging from tanks containing C. maenas fed 20 M. balthica day^− 1 reacted by increasing their burial depths from approximately 30 mm to depths of > 60 mm, over a period of several days. When the signal was removed the bivalves gradually returned to their original depth over 5 days. C. edule similarly exposed to effluent from crabs feeding on conspecifics showed no response. In an attempt to identify the signal inducing this burrowing response, M. balthica were exposed to a variety of chemical signals. Crabs fed M. balthica elicited the strongest response, followed by crabs fed C. edule. There were also small responses to effluent from crabs fed on fish, crabs previously fed on M. balthica and to crab faeces, but no responses to starved crabs, crushed M. balthica, or controls. We conclude that increased burrowing depth of M. balthica is induced by some as yet unidentified chemical cue produced by feeding crabs and is strongest when the crabs were fed on M. balthica. Unexpectedly, neither the presence of crabs themselves, nor of damaged conspecifics, was effective in eliciting a burrowing response. The mortality rates of M. balthica and C. edule selected by crabs when burrowed at normal depths and after exposure to effluent from feeding crabs were different. Crabs selected 1.5 times more C. edule than M. balthica when both species were burrowed at their normal depths, but 15 times more after the tanks had been exposed to effluent from feeding crabs for 5 days. The burrowing response of M. balthica thus appears to reduce mortality significantly by displacing predation pressure on to the more accessible C. edule.     

Ventilation and control of acid-base status during temperature acclimation in the crab,Cancer magister

Summary Frequencies of scaphognathite (ventilatory,f _sc) and heart (f _h) pumping, oxygen consumption ( ), and hemolymph oxygen, carbon dioxide and pH levels were measured in adult Dungeness crabs (Cancer magister) during 7–10 day periods of exposure to 7, 12, and 17°C seawater. Ventilation volume ( ) was calculated for individual animals fromf _sc and a previously determined relationship between stroke volume and animal mass. increases (Q₁₀=2.3) with temperature were associated with larger increases inf _sc (Q₁₀=3.3) and (Q₁₀=3.5) and smaller increases inf _h (Q₁₀=1.5). The incidence of unilateral scaphognathite pumping and pausing decreased as temperature rose.Postbranchial oxygen tension was maintained in vivo but hemolymph oxygen content decreased both in vivo and in vitro as temperature rose. Postbranchial carbon dioxide tension did not change significantly but relative alkalinity was maintained as temperature rose by loss of hemolymph bicarbonate. The effects of increased ventilation volume and potential mechanisms of bicarbonate regulation are discussed.The responses of the essentially subtidalCancer magister are compared with those of subtidal, intertidal and terrestrial crabs demonstrating that the concepts of acid-base regulation developed for water and air breathing vertebrates are also applicable to water and air breathing crabs, and that intertidal crabs may exhibit transitional states.This work was supported by Grant No. A.5762 National Research Council of Canada     

Immunotoxic effects of nickel in the mud crab Scylla serrata

The presence of xenobiotic contaminants especially metals in coastal waters is a major concern as they are immunotoxic to aquatic animals even at low concentrations. In our present study, mud crab Scylla serrata was exposed to three sublethal concentrations (0.4, 0.6 and 0.8 mg/L) of nickel for 30 days under laboratory conditions and the alterations of hematological parameters like haemocyte count, clotting time, haemocyte viability, protein content and immunomodulatory components like phenoloxidase, phagocytosis and superoxide anion generation were measured. In addition, the accumulation patterns of nickel were measured in gills, hepatopancreas and ovary. The accumulation was more in gills when compared to hepatopancreas and ovary of crabs exposed to nickel and was not detected in the control crabs. The results revealed a significant (P < 0.05) induction of superoxide anion generation and phagocytosis activity in the haemolymph of the crabs exposed to nickel when compared to control. On the contrary, the rest of the parameters were significantly (P < 0.05) reduced in the experimental groups when compared to the control. All the studied parameters exhibited a concentration dependent response.     

Oxygen consumption and the respiratory responses to declining oxygen tension in the crab Ebalia tuberosa (Pennant) (Crustacea: Decapoda: Leucosiidae)

Oxygen consumption and its relationship to body weight and activity have been examined in Ebalia tuberosa (Pennant). Ebalia showed only very limited ability to regulate their oxygen consumption under conditions of declining P_O2. Respiratory independence was markedly affected by the level of activity of the animals. When inactive, respiratory independence was maintained down to a critical P_O2 of only about 130 mm Hg while when active, the crabs behaved as perfect conformers. Inactive Ebalia responded to a decrease in PO₂ by increasing the pumping activity of the scaphognathites and heart. This increased activity continued even at oxygen tensions lower than the P_c. The rate of reversals of the ventilatory currents did not change with decreasing P_O2. In the active crabs, the pumping activity of the scaphognathites and heart, and the rate of current reversals were higher than in the inactive animals, and a decrease in PO₂, did not bring about any further change in any of these responses. When exposed to hypoxic conditions for long periods initially inactive crabs survived longer than did active animals.     

Bitter crab syndrome in two species of king crabs from the Sea of Okhotsk

The disease caused by parasitic dinoflagellates of the genus Hematodinium was found in the red Paralithodes camtschaticus and blue P. platypus king crabs from the Sea of Okhotsk. The hemolymph of diseased crabs was cream colored, opaque, and dense. Numerous dinokaryotic trophonts and multinucleate plasmodia of the parasite were revealed in the hemolymph and internals of diseased animals. The parasitic infection was recorded in females and juvenile males from August to mid-October.     

Effect of fasting and refeeding on gluconeogenesis and glyconeogenesis in the muscle of the crab Chasmagnathus granulatus previously fed a protein- or carbohydrate-rich diet

The present study investigated the participation of the muscle gluconeogenic and glyconeogenic pathways in lactate metabolism after 15 fasting and during different periods of refeeding in Chasmagnathus granulatus previously maintained on a carbohydrate-rich (HC) or high-protein (HP) diet. In C. granulatus the metabolic adjustments during the fasting use different pathways according to the composition of the diet previously offered to the crab. During fasting, the gluconeogenic capacity is reduced in crabs maintained on the HC diet. In animals maintained on the HP diet, an increase in activity of the glyconeogenic pathway occurs after 15 days of fasting. In the animals fed HC diet, the glyconeogenesis is one of the pathways responsible for maintenance of the lactate levels in the fed and refeeding states. In crabs fed on the HP diet, the gluconeogenesis and glyconeogenesis pathways are involved in the reduction of lactate levels during the refeeding period. This study shows that protein or carbohydrates levels in the diet previously administrated to the crabs modulate the gluconeogenesis, glyconeogenesis in muscle and lactate concentration in the hemolymph in fed, fasting and refeeding states.     

Predation by gulls on crabs in rocky intertidal and shallow subtidal zones of the Gulf of Maine

Most organisms in intertidal areas are marine in origin; many have distributions that extend into the subtidal zone. Terrestrial predators such as mammals and birds may exploit these animals during low tide and can have considerable effects on intertidal food webs. Several studies have shown that avian predators are capable of reducing densities of sessile and slow-moving intertidal invertebrates but very few studies have considered avian predation on mobile invertebrate predators such as crabs. In this study, we investigated predation by Great Black-backed Gulls (Larus marinus Linnaeus) on three species of crabs (Cancer borealis Stimpson, Cancer irroratus Say, and Carcinus maenas Linnaeus). The study was at Appledore Island, ME (a gull breeding island) and 8 other sites throughout the Gulf of Maine, including breeding islands and mainland sites. On Appledore Island, intertidal and subtidal zones provided over one-third of prey remains found at gull nests, and crabs were a substantial proportion (∼ 30% to 40%) of the total remains. Similarly, collections of prey remains from intertidal areas indicated that crabs were by far the most common marine prey. C. borealis was eaten far more often and C. irroratus and C. maenas less often than expected at each site. Comparing numbers of carapaces to densities of crabs in low intertidal and shallow subtidal zones at each site, we estimated that gulls remove between 15% and 64% of C. borealis during diurnal low tides. The proportion of C. borealis eaten by gulls was independent of proximity to a gull colony. Approximately 97% of the outer coast of Maine is within 20 km of a breeding island. Thus, a lot of gull predation on crabs may occur throughout the Gulf of Maine during summer months. Crabs are important predators of other invertebrates; if predation by gulls reduces the number of crabs in intertidal and shallow subtidal areas, gulls may have important indirect effects on intertidal food webs.