Fungus invasion of legs of the tanner crab, Chionoecetes bairdi

Histological examination of tissues from the legs of tanner crabs, Chionoecetes bairdi, infected with black mat fungus, Trichomaris invadens, showed that hyphae penetrated the cuticle of the crab, extensively invaded the epidermis, and extended into the muscle tissue.     

Fungus invasion of legs of the tanner crab, Chionoecetes bairdi.

Histological examination of tissues from the legs of tanner crabs, Chionoecetes bairdi, infected with black mat fungus, Trichomaris invadens, showed that hyphae penetrated the cuticle of the crab, extensively invaded the epidermis, and extended into the muscle tissue.     

Observations on the histopathology and probable progression of the disease caused by Trichomaris invadens,an invasive ascomycete,in the Tanner crab,Chionoecetes bairdi

Fifty-three Tanner crabs with varying degrees of surface encrustations and internal invasion by Trichomaris invadens were necropsied, processed, and examined to determine the extent of internal tissue invasion and histopathological effects of the infection. Sufficient data were accumulated to provide some insight on the progression, but not the rate, of tissue invasion. The epidermis and subepidermal layers are invaded and virtually replaced by proliferating hyphae. The invasion then proceeds internally, predominantly via the connective tissue. Major muscles and blood vessels are invaded, then invasion of deeper organs, including the hemopoietic tissue, gastrointestinal tract wall, and wall of the heart follows. The eyestalk is infected, usually early in the disease, and the invasion follows a similar pattern to that in the cephalothorax. Massive invasion and destruction of the retina is the major pathological effect. The gill may also be involved, with destruction of the lamellar tissues and invasion and destruction of podocytes in the stem of the gill.     

Histopathology of the mangrove land crab Ucides cordatus (Ocypodidae) affected by lethargic crab disease

Lethargic crab disease (LCD) has caused extensive epizootic mortality of the mangrove land crab Ucides cordatus (Linnaeus 1763) (Brachyura: Ocypodidae) along the Brazilian coast. Direct culture of tissue samples from sick crabs and subsequent isolation and purification identified the causative agent as an Exophiala species of fungus. The histopathology of crabs with variable signs of LCD indicates that the most affected tissues are the epidermis, connective tissue, heart, hepatopancreas, nervous system, and gills. Gonads, somatic muscles, and digestive system are less affected by the fungus. The observed pathology is compatible with the clinical signs of LCD. Necrosis, tissue degeneration, and congestion of hemal sinuses and vessels are present in heavily infected organs. Nerve fibers may be compressed by accumulations of yeast-like cells. In heavy infections the tissue of gill lamellae is destroyed with subsequent dilation or compression. Cellular immune responses include hemocytic infiltration, agglutination and encapsulation, and phagocytosis. Phagocytosis of yeast-like cells is abundant in the connective tissue associated with the exoskeleton. These results indicate that LCD is the result of a systemic phaeohyphomycosis caused by a species of Exophiala. The present study also suggests that dispersal of the fungus within the crab occurs through the hemal system.     

The influence of starvation and copper exposure on the composition of the dorsal carapace and distribution of trace metals in the shore crab Carcinus maenas (L.)

1. The influence of starvation and copper exposure on the composition of the carapace of the shore crab, Carcinus maenas has been investigated. The effects of the concentrations of selected trace metals in the carapace and midgut gland have also been examined.2. Differences in nutritional state did not affect the concentrations or relative proportions of the principle carapace components (calcium, chitin and protein), but starvation was associated with a reduction in carapace copper concentration. Copper concentration in the midgut gland increased in “starved” crabs, while midgut gland zinc and calcium concentrations remained unchanged.3. Starvation in combination with copper exposure (0.5 mg Cu/1) resulted in alterations in both carapace composition and trace metal loads. Carapace calcium concentrations were reduced significantly following copper exposure irrespective of the nutritional state of the crabs. However, the reduction was more marked in “fed” crabs than in “starved” animals.4. Copper-exposed crabs exhibited raised carapace copper concentrations while carapace zinc concentrations were depressed. Such changes were most pronounced in copper-exposed “starved” crabs.5. Calcium concentrations in the midgut glands of “starved” copper-exposed animals were significantly elevated compared with those in either control or “fed”, copper-exposed crabs.6. The findings are discussed with regard to their ecotoxicological significance.     

A trematode metacercaria encysted in the nerves of the dungeness crab, Cancer magister

Of 188 Dungeness crabs, Cancer magister, 8 contained unidentified trematode metacercariae encysted in various components of the nervous system, including the thoracic ganglion, brain, lamina ganglionaris of the eyestalk, and major nerves arising from the thoracic ganglion. A single cyst was present in the available tissue sections of 7 of the crabs and no behavioral abnormalities were exhibited. One crab with multiple cysts in major nerves near the thoracic ganglion was markedly ataxic. The cysts and included worms distorted, compacted, and destroyed nervous tissue, and occupied most of the nerves where present. Host response was minimal, but some cysts invoked massive hemocytic accumulations near the infection site. Infections probably seriously affect nerve impulse transmission and accounts for the lethargic behavior of the crab with multiple cysts in major nerves. The present report is the first record of digenetic trematode infections in the Dungeness crab and the apparent restriction of the worm to nervous tissue is unusual if not unique in the Digenea. Because of the absence of grossly recognizable lesions and the small samples excised at necropsy, both the incidence and intensity of infection in Dungeness crab populations are almost certainly higher than indicted by our data.     

Hole boring of crustacean prey by the octopus Eledone cirrhosa (Mollusca, Cephalopoda)

Eledone cirrhosa has been found to make a borehole in the carapace of a high proportion of its crustacean prey. This is the first account of drilling in crustaceans by octopus. The frequency of incidence of the boring behaviour varied between prey species from 17 to 93% of those killed. The incidence of boreholes was higher in crabs killed by small octopuses. Using crabs mainly of the genera Cancer, Carcinus, Corystes and Macropipus , the distribution and orientation of the boreholes was recorded. The boreholes occurred in any part of the carapace but the great majority were found close to the mid-line and in the posterior half. The long axis of the oval penetration was usually aligned with the anteroposterior axis of the crab. The Mediterranean species Eledone moschata was also found to bore crabs, and newly hatched juveniles of this species are capable of boring as early as their second killing of a live crab. No evidence was found that Octopus vulgaris normally bores the carapace of crabs.     

The diet of the Harlequin crab Lissocarcinus orbicularis,an obligate symbiont of sea cucumbers (holothuroids) belonging to the genera Thelenota,Bohadschia and Holothuria

The present paper characterizes, for the first time, the diet of the Harlequin crab Lissocarcinus orbicularis, an obligate symbiotic crab that associates with sea cucumbers (holothuroids) belonging to the genera Thelenota, Bohadschia and Holothuria. These tropical holothuroids host a rich symbiotic community in the Indo-West Pacific Ocean of which the Harlequin crab is the best known. The diet of L. orbicularis was characterized by analyzing the microscopic, molecular and isotopic signatures obtained from its gastric content. The presence of sea cucumber ossicles in the gastric mills of the crabs suggests that symbionts eat the superficial integument of their host and this was supported by the fact that Holothuroid DNA was detected in the stomach of L. orbicularis after DGGE and sequencing of the 18S rDNA gene. The stable isotopic δ¹³C and δ¹⁵N values of crab tissues were compared with diverse potential food sources including three holothuroids, three algae, one sea grass as well as the organic matter contained in the water column, in the sediment, and the second most abundant symbiont, the polychaete Gastrolepidia clavigera. The low δ¹⁵N values of crabs suggests that the crabs do not exclusively feed on sea cucumber tissue but assimilate diverse food sources such as sea grasses and organic matter contained in sediment that have similar δ¹³C values. There were no differences between the feeding of males and females but there was a positive correlation between the carapace length and the stable isotopic values indicating a shift of the food source as crabs grow larger.     

Regeneration of Limbs in Males of the Tanner Crabs Chionoecetes bairdi and Ch. Opilio

The frequency of the loss of pereiopods and the features of their regeneration were studied in males of the tanner crabs Chionoecetes bairdi and Ch. opilio, sampled in the Sea of Okhotsk in 2001. It was established that after the loss of an appendage a complete recovering of body symmetry in both crab species occurs in four moltings, during which the length of the regenerating pereiopod averages respectively 39–41, 70.5, 89.5, and 96–97% of the norm. The patterns of limb regeneration were compared between tanner crabs and representatives of fam. Lithodidae.     

Quantifying factors influencing American lobster (Homarus americanus) predation on the invasive green crab (Carcinus maenas) in Newfoundland,Canada

The European green crab (Carcinus maenas) is a newly invasive species in Newfoundland, where it has likely been present for ≤15 years. The green crab has been found in stomach contents of American lobster (Homarus americanus) in New England and Nova Scotia, Canada, but predation on this species has not yet been quantified in Newfoundland. We conducted feeding experiments to determine whether lobsters from Newfoundland were as likely as those from Nova Scotia (which have coexisted with green crabs for >60 years) to recognize and prey upon this new species. We also performed experiments to determine whether green crabs reach a size refuge from predation and whether factors including starvation, availability of alternate food sources, or habitat complexity would influence the probability of lobster attacking or feeding on green crabs. In our trials, lobster origin had no significant effect on crab predation; lobsters, irrespective of origin, were more likely to consume small (<40 mm carapace width [CW]) and medium (40–65 mm CW) crabs than larger (>65 mm CW) ones. Nevertheless, even small lobsters (73–76 mm carapace length, 300 g) were able to kill and consume the largest green crabs (78 mm CW, 100 g). Green crabs were less likely to be attacked or eaten when an alternative food source was present, suggesting that the lobsters were preying on the crabs, rather than simply killing them in a dispute over territory. The addition of a shelter provided a refuge for the green crabs; however, the crabs were only able to avoid being injured or eaten if this shelter was structurally complex. The green crab is slowly spreading westward around the island of Newfoundland, and so its long‐term effects, interactions with other organisms, and contribution to the diet of Newfoundland lobsters remain to be seen.     

The ectosymbiont crab Dissodactylus mellitae-sand dollar Mellita isometra relationship

The presence of the ectosymbiont Dissodactylus mellitae on Mellita isometra was studied at Tybee Island in Georgia. The number of crabs found on sand dollars, stage of maturity, sex, numbers of eggs, and size of eggs produced by crabs were noted. The test diameter of sand dollars, and the number and diameter of eggs produced were also noted. Infestation rates of crabs on sand dollars varied over time. The maximum number of crabs found on a sand dollar was 10. The three types of population dispersion, random, uniform, and clumped, were observed for crabs on sand dollars throughout the sampling period. Clumped or gregarious settling was observed when juvenile crabs were abundant, uniform and random distribution when mature crabs were abundant. Female crabs were significantly larger than male crabs, with carapace width of the largest mature female crab being 4.6 mm and the largest male 3.1 mm. Crabs produced between 80 and 300 eggs from 0.188 to 0.291 mm in diameter. Bigger crabs produced significantly more eggs than smaller crabs. Sand dollar sizes were 50-110 mm, with a mode between 60 and 70 mm. The effect of crab burden on egg production in the sand dollar was time-dependent. The presence of crabs on sand dollars correlated with total egg production of sand dollars in May, the peak of the spawning season, with sand dollars carrying one or two crabs having a lower egg production than those without crabs. Overall, variation in egg size was attributed to variation among females followed by variation between seasons and crab burden.     

A new shell disease in the mud crab Scylla serrata from Port Curtis, Queensland (Australia)

In 1994 a previously unreported rust spot shell disease was seen in mud crabs Scylla serrata - Forskal from Port Curtis, central Queensland, Australia. Of 673 crabs surveyed, 21.7% had shell lesions. Of these, 82.9% had rust spot lesions on the carapace. The majority of rust spot-affected crabs (78.8%) were female. Rust spot lesions were predominantly non-perforated (89.4%) and 54.8% were bilaterally symmetrical. There was also a gender difference in the areas of the carapace most commonly affected. The main histological features of the rust spot lesion included: a cavity in the upper endocuticle; indentation of the endocuticle below the cavity; remains of muscle attachment adhesive epithelium within the cavity; fibrous connective tissue between the damaged carapace and the attached muscle; and islands of endocuticle in this fibrous connective tissue. Histopathology of the internal organs failed to find evidence of an infectious or parasitic cause of the rust spot lesions. The cause(s) of the syndrome appear(s) to be non-infectious.     

The occupation of artificial burrows by Helice tridens (De Haan) and the length of its stay

The mud-crab Helice tridens (De Haan) influences the cycling of matter in salt-marsh ecosystems through its burrowing activity. If the crabs occupy and stay in their burrows for a short time, their burrowing activity will be great, since they will continuously construct new burrows. Therefore, investigation of the relation between the crabs and their burrows is considered to be important. In the present study, the relation between pipes as a form of artificial burrow and their occupation by the crab was analyzed. A close relationship was recognized between the diameter of the pipe opening and the carapace width of the crab which occupied the pipe, while pipes with a length shorter than the depth of the crab burrows were hardly occupied. These results indicate that the diameter and length of an artificial burrow affects the likelihood of its occupation by this species of crab. The length of the crab's stay in this type of artificial burrow was generally 1 day. This result may be related to the field observation that newly made burrows frequently collapse due to water current occurring through tidal action after the crabs have left.     

稻田网箱养殖辽河水系中华绒螯蟹幼蟹的个体生长

本实验在室外网箱内监测辽河水系中华绒螯蟹(Eriocheir sinensis)幼蟹阶段个体生长发育的每一次蜕壳生长情况。2013年实验选取雄蟹和雌蟹各200只,记录了每个蜕壳阶段雌蟹和雄蟹的生长,包括壳长、壳宽、总重和蜕壳间隔时长(d),并且观察雌蟹和雄蟹形态特征的变化。实验共进行111 d,幼蟹共蜕壳11次。实验结束时,雄蟹剩余34只,雌蟹剩余42只;雄蟹的特定生长率为(7.176 5±0.168 4)%/d,雌蟹的特定生长率为(7.283 3±0.174 3)%/d;雌蟹生长蜕壳过程中腹部的形态变化大,腹部由三角形变成卵圆形;雄蟹在生长蜕壳过程中螯足的增长明显较雌蟹快,并且在本实验最后一次即第11次蜕壳后螯足腹面内侧出现1小撮绒毛,外侧也出现少量绒毛,但不易被发现。     

Evidence for a permanent establishment of the snow crab (Chionoecetes opilio) in the Barents Sea

In the Atlantic the snow crab (Chionoecetes opilio) is naturally distributed on the northwestern side, i.e. eastern Canada and west Greenland. Until recently, there have been no observations of snow crab in eastern Atlantic. However, in 1990s single and occasional reports were made of crabs captured in the eastern part of the Barents Sea, presumably introduced through ballast water. Special attention during the annual bottom-trawl surveys in the Barents Sea during February 2004–2006 were given to include recordings of snow crab to evaluate if the introduced species has succeeded to establish a self-sustaining population in this region. Recordings of snow crabs were systematically noted and biological measurements carried out. The results confirm previous Russian observations of snow crabs in the northern region of Gåsebanken. In addition, a significant number of crabs were also found in the central region of the Barents Sea, mainly in deeper waters from 180 to 350 m depth. The sizes ranged from 14 to 136 mm carapace width. All females above 70 mm were berried with fertilised eggs. A major fraction (31% in 2005; 76% in 2006) of the crabs consisted of juveniles below 50 mm CW, providing evidence for successful recruitment. The small-sized crabs were exclusively found in Gåsebanken, identifying the main recruiting area at present for snow crab in the Barents Sea. The results obtained show that the snow crab is now adapted to the northeast Atlantic.     

Molt-inhibiting hormone immunoreactive neurons in the eyestalk neuroendocrine system of the blue crab, Callinectes sapidus

The production of ecdysteroid molting hormones by crustacean Y-organs is negatively regulated by a neuropeptide, molt-inhibiting hormone. It is generally agreed that molt-inhibiting hormone is produced and released by the eyestalk neuroendocrine system. In the present study, immunocytochemical methods were used to detect molt-inhibiting hormone immunoreactive neurons in eyestalk ganglia of the blue crab, Callinectes sapidus. The primary antiserum used was generated against molt-inhibiting hormone of the green shore crab, Carcinus maenas. A preliminary Western blot analysis indicated the antiserum binds molt-inhibiting hormone of Callinectes sapidus. Using confocal and conventional immunofluorescence microscopy, molt-inhibiting hormone immunoreactivity was visualized in whole mounts and thin sections of Callinectes sapidus eyestalk ganglia. Immunoreactivity was detected in 15-25 neurosecretory cell bodies in the medulla terminalis X-organ, their associated axons and collateral branches, and their axon terminals in the neurohemal sinus gland. The cellular organization of molt-inhibiting hormone immunoreactive neurons in blue crabs is generally similar to that reported for other crab species. The combined results suggest the cellular structure of the molt-inhibiting hormone neuroendocrine system is highly conserved among brachyurans.     

Infection by a Hematodinium-like parasitic dinoflagellate causes Pink Crab Disease (PCD) in the edible crab Cancer pagurus

The edible crab (Cancer pagurus) supports a large and valuable fishery in UK waters. Much of the catch is transported live to continental Europe in specially designed live-well ('vivier') vehicles. During the winter of 2000/2001, many trap-caught crabs from Guernsey, Channel Islands, UK, were reportedly moribund and pink in colour. These crabs generally died before and during vivier transportation. We provide histological, immunological, and molecular evidence that this condition is associated with infection by a Hematodinium-like dinoflagellate parasite similar to that previously reported in C. pagurus and to an infection causing seasonal mass mortalities of the Norway lobster (Nephrops norvegicus). Pathologically, every altered host bore the infection, which was characterised by very large numbers of plasmodial and vegetative stages in the haemolymph and depletion of reserve cells in the hepatopancreas. Due to the hyperpigmentation of the carapace and appendages, we have called this infection 'Pink Crab Disease' (PCD). Similar Hematodinium infections cause 'Bitter Crab Disease' in tanner and snow crabs, which has had a negative effect on their marketability. At present, little is known about the seasonality, transmission, and market impact of this infection in C. pagurus.     

Agonistic interactions between invasive green crabs, Carcinus maenas (Linnaeus), and sub-adult American lobsters, Homarus americanus (Milne Edwards)

The invasive green crab, Carcinus maenas, has recently expanded its range into the Southern Gulf of St. Lawrence, where there is potential for substantial niche overlap with juvenile American lobsters, Homarus americanus. We used two experiments to elicit, record and analyze the agonistic interactions of adult green crabs (carapace width of 63-75 mm) and sub-adult (carapace length of 55-70 mm) lobsters. The first experiment gave each animal equal access to a limited food resource. The green crabs were first to the food in significantly more trials, spent a significantly greater proportion of time with the food, and were able to successfully defend the food from attacks by the heavier lobsters. In the second experiment, we allowed the lobsters to gain possession and initiate feeding on the food before releasing the green crabs. In these trials, the lobsters spent significantly more time with the food, and were able to defend the food from the green crabs. The results of both experiments are discussed in the context of game theory. The different behaviour of the crustaceans in the two experiments is consistent with the “bourgeois” strategy in a hawk and dove game simulation. With this strategy, an animal acts like a hawk if in possession of a resource, but acts like a dove if the other animal is in possession of the resource. The fact that the green crabs were able to physically compete with, and in many cases dominate the larger, heavier lobsters supports the potential for competitive impacts of green crabs on sub-adult lobsters.     

Infestation Level of the Crab Hemigrapsus sanguineus by a Parasitic Crustacean Polyascus polygenea (Crustacea: Cirripedia) in Vostok Bay, Sea of Japan

We studied the infestation level of the coastal crab Hemigrapsus sanguineus by a cirripede barnacle Polyascus polygenea in Peter the Great Bay (Vostok Bay, Sea of Japan) in 1998–1999. It is shown that the externae of the parasite usually appear on the surface of the host’s body at the time when the crab attains sexual maturity (at a carapace width of 14–15 mm). More often we encountered infested crabs of a medium size, with a carapace width of 25–29 mm. The level of crab invasion did not depend on the sex of the host. In the summer period the proportion of infested crabs in different habitats ranged from 7 to 84%. The greatest number of crabs bearing the externae of the parasite was registered in an area with a boulder-pebble surface and small surf waves.Original Russian Text Copyright © 2005 by Biologiya Morya, Korn, Akhmadieva, Rybakov, Shukalyuk.     

Habitat partitioning between prey soldier crab Mictyris brevidactylus and predator fiddler crab Uca perplexa

Interaction and habitat partition between the soldier crab Mictyris brevidactylus (prey) and the fiddler crab Uca perplexa (predator) were examined at a sandy tidal flat on Okinawa Island, Japan, where they co-occur. Both live in dense colonies. When the soldier crabs were released in the densely populated habitat of the fiddler crab, male fiddler crabs, which maintain permanent burrows in hard sediment, preyed on small soldier crabs and repelled large ones. Thus, the fiddler crabs prevented the soldier crabs from trespassing. It was also observed whether soldier crabs burrowed successfully when they were released 1) where soldier crab burrows just under the sand were abundant, 2) in a transition area between the two species, 3) an area without either species, and 4) where artificial tunnels simulated soldier crabs' feeding tunnels were made by piling up sand in the area lacking either species. In contrast to the non-habitat area, many soldier crabs burrowed in the sediment near the release point in the tunnel, transition and artificial tunnel areas. This indicates that the feeding tunnels on the surface attracted other crabs after emergence. When the large male fiddler crabs were transplanted into the artificial burrows made in soft sediment of the soldier crab habitat, all left their artificial burrows by 2 days. In the fiddler crab habitat, however, about one-third of the transplanted male fiddler crabs remained in the artificial burrows after 3 days. The soldier crabs regularly disturb the sediment by the up and down movement of their burrow (small air chamber) between tides. This disturbance probably prevents the fiddler crab from making and occupying permanent burrows. Thus, it appears that these crabs divide the sandy intertidal zone by sediment hardness and exclude each other by different means.