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.     

An experimental evaluation of host specificity: the role of encounter and compatibility filters for a rhizocephalan parasite of crabs

The encounter/compatibility paradigm of host specificity provides three qualitative pathways to the success or failure of a potential host-parasite interaction. It is usually impossible to distinguish between two of these (encounter and compatibility filters closed versus encounter filter open and compatibility filter closed) because unsuccessful infection attempts are difficult to observe in nature. We were able to open the encounter filter under experimental laboratory conditions. Our analytical system used the rhizocephalan barnacle, Sacculina carcini, a parasitic castrator of the European green crab, Carcinus maenas, and Pachygrapsus marmoratus, a native European crab that occurs with C. maenas but is not parasitized by S. carcini in nature. Penetration followed by unsuccessful infection of P. marmoratus crabs by parasitic barnacle larvae leaves a uniquely permanent record in the thoracic ganglion of the crabs. This provided us with a novel tool to quantify the encounter filter in a host-parasite system in nature. We demonstrated, in the laboratory, that the compatibility filter was closed and that, in nature, even where barnacle larvae were present, the encounter filter was also effectively closed. The closure of both filters in nature explains the failure of this potential host-parasite interaction, an outcome favored by selection in both host and parasite.     

Microbial communities are indicators of parasite infection status

Growing evidence suggests that microbiomes have been shaping the evolutionary pathways of macroorganisms for millennia and that these tiny symbionts can influence, and possibly even control, species interactions like host–parasite relationships. Yet, while studies have investigated host–parasites and microbiomes separately, little has been done to understand all three groups synergistically. Here, we collected infected and uninfected Eurypanopeus depressus crab hosts from a coastal North Carolina oyster reef three times over 4 months. Infected crabs demonstrated an external stage of the rhizocephalan parasite, Loxothylacus panopaei. Community analyses revealed that microbial richness and diversity were significantly different among tissue types (uninfected crab, infected crab, parasite externae and parasite larvae) and over time (summer and fall). Specifically, the microbial communities from parasite externae and larvae had similar microbiomes that were consistent through time. Infected crabs demonstrated microbial communities spanning those of their host and parasite, while uninfected crabs showed more distinctive communities with greater variability over time. Microbial communities were also found to be indicators of early-stage infections. Resolving the microbial community composition of a host and its parasite is an important step in understanding the microbiome's role in the host–parasite relationship and determining how this tripartite relationship impacts coevolutionary processes.     

Parasites of the shore crab Carcinus maenas (L.): implications for reproductive potential and invasion success

The European shore crab, Carcinus maenas, is one of the most successful marine invasive species. Its success has been in part attributed to the loss of parasites, rekindling an interest in host-parasite interactions and impacts on host fitness in this crab. In the present study, we investigated C. maenas populations from Europe, South Africa and Australia for parasites, and assessed their impact on the fitness of male crabs. For the shore crab, testes weight along with success in mating competition is traded off against other life-history traits. We therefore used this parameter as an indicator both for reproductive fitness and a possible resource trade-off in response to parasite infestation. In the native range, crabs infested with Sacculina carcini showed significantly lower testes weight than uninfected crabs. However, helminth parasites did not generally cause reduced testes weights. Crab populations from South Africa and Australia were either parasitized at very low prevalences, or were completely parasite free. However, no population level effect of this parasite release was reflected in testes weight. These findings do not support a severe fitness impact of helminth parasites on C. maenas, which questions the role of parasites on its population dynamics, both in the native area and for invasive success.     

Differences in the parasitic effects of a bopyrid isopod and rhizocephalan barnacle on the portunid crab,Charybdis bimaculata

Bopyrid isopods and rhizocephalan barnacles are obligate parasite crustaceans which harm their decapod hosts. However, to the best of our knowledge, studies have not compared which of these parasites has a greater parasitic effect on its hosts. Here, the parasitic effect of the bopyrid isopod, Allokepon hendersoni, and an unidentified sacculinid rhizocephalan species, infesting the same population of portunid crabs, Charybdis bimaculata, was investigated and compared for the first time. Samples were collected from the bycatch of a trawl fishery in Tosa Bay, Japan. A total of 2601 crabs were collected, of which 14 (0.55%) were parasitized by the bopyrid and 21 (0.82%) by the rhizocephalan. One of the two female crabs parasitized by the bopyrid was ovigerous (with much fewer eggs than unparasitized females). No ovigerous crab was found from the eight females parasitized by the rhizocephalan. Because only two female crabs were parasitized by the bopyrid, the following analyses were made using the male crabs. Both parasites reduced the wet weight (crab condition) and the cheliped size (secondary growth) of C. bimaculata, but the impact of the parasitism did not differ between the parasite species. The size of the abdominal flap of male hosts was reduced by the bopyrid infestation; however, rhizocephalan infestation caused enlargement of the abdominal flap, which is an indication of feminization. The present study provides information on how the effect of these two parasitic castrators on the same host crab varies. A moderate decrease in crab condition and cheliped development was common among the parasites, suggesting that the degree of impact might be favorable for the survival of the two parasites species.     

A review of the parasitic dinoflagellates Hematodinium species and Hematodinium-like infections in marine crustaceans

Parasitic dinoflagellates in the genus Hematodinium are important parasites of marine Crustacea. Outbreaks of these parasites have damaged commercial stocks of Norway lobster Nephrops norvegicus, snow crab Chionoecetes opilio, Tanner crab C. bairdi, American blue crab Callinectes sapidus, and velvet swimming crab Necora puber. Species of Hematodinium can reach high enough levels to regulate their host populations, but mortalities are also centred on the unfished juveniles and females, hosts not normally sampled by fisheries; hence impacts are often underreported. Seasonal prevalences of up to 85 % occur annually in many host populations; in effect, these parasites form cryptic blooms in the water column with crabs and other crustaceans at risk of disease. We review the biology and ecology of Hematodinium spp. infections in crustaceans. Included is a comparison of the different infections, a synthesis of what is known, and an attempt to highlight fruitful areas for continued research.     

Epizootiology of the parasitic dinoflagellate Hematodinium sp. in the American blue crab Callinectes sapidus

Hematodinium sp. is a parasitic dinoflagellate that infects and kills blue crabs Callinectes sapidus. Periodic outbreaks of dinoflagellate infections with subsequent high host mortalities prompted a study of the epizootiology and distribution of the crab pathogen. Hemolymph samples from over 13000 crabs were assessed for infections over 8 yr. Moderate to high prevalences were found at several locations along the Atlantic and Gulf coasts of the United States. In the coastal bays of Maryland and Virginia, prevalence followed a seasonal pattern, with a sharp peak in late autumn. Infections were significantly more prevalent in crabs measuring less than 30 mm carapace width; host sex did not influence prevalence. Prevalences were highest in crabs collected from salinities of 26 to 30%o; no infected crabs were found in salinities below 11%o. Intensity of infection did not vary among crab sizes, molt stages, or sexes. Naturally and experimentally infected crabs died over 35 and 55 d in captivity, with a mean time to death of approximately 13 and 42 d, respectively. Several other crustaceans, including gammaridean amphipods, xanthid (mud) crabs, and the green crab Carcinus maenus, were found with Hematodinium-like infections. Considering its widespread distribution and high pathogenicity, we suggest that Hematodinium sp. represents a significant threat to blue crab populations in high salinity estuaries along the Atlantic and Gulf coasts of the USA.     

A trematode infection with no effect on reproductive success of a sand-bubbler crab

The infection effects of the parasitic digenean trematode on the body weight and reproductive success of the sand-bubbler crab were examined. Gynaecotyla squatarolae (Trematoda: Microphallidae) infects the body cavity of Scopimera globosa (Decapoda: Scopimeridae) and uses the crab as its second intermediate host. The parasites infected all reproductive crabs examined to varying degrees. Larger crabs of both sexes had more parasites than smaller ones, probably because body size reflects age, and older crabs had a longer period of exposure to infection. Males had more parasites than females, probably because of sexual difference in acting time on the surface. Ovigerous females stay in closed burrows and do not act on the surface during incubation, and so have less chance of infection than males. The quantity of infecting parasites did not explain variations in either body weight or reproductive success of individual crabs in a field experiment. The life history of this parasite, relative body size of the crabs, and cost and the possible benefit of manipulation for the parasite may explain these results.     

滨鹬马蹄吸虫(复殖目:微茎科)的尾蚴和囊蚴期的季节动态

对科威特湾微茎科滨鹬马蹄吸虫幼虫期的中间宿主双带盾桑椹螺(Clypeomorus bifasciata)及小相手蟹(Nanosesarma minutum)的季节动态进行了研究。调查期超过一年,在检查的1 600只螺和415只蟹中, 11.8 %的螺感染了8种马蹄属线虫中的一种,且以滨鹬马蹄吸虫的感染占优势(9.9 %螺感染) ; 80 %的蟹感染滨鹬马蹄吸虫囊蚴。虽然一年四季两种宿主都会感染,但吸虫的流行和尾蚴(指成熟期感染)在夏季呈现高蜂。从螺体排出的尾蚴具有明显季节性,在此海湾必须要超过最低温度20℃。总的感染率在较大(较老)的螺里有所下降,显示吸虫影响宿主生存并随之影响宿主群体结构。囊蚴的感染丰度与蟹的个体大小有明显相关性;较大的蟹感染较多的囊蚴,显示宿主能耐受更多的吸虫。调查显示,囊蚴的感染率与蟹的大小或性别无相关性。囊蚴体外脱囊以及产卵吸虫的释放证明,成熟虫体终年存在于所有大小和性别不同的蟹里,显示从蟹到鸟的持续感染是可能的。总的来说,滨鹬马蹄吸虫在海湾的传播动态是由这两种无脊椎动物宿主来协调,并似乎是被一系列依赖于温度的活动控制,这些活动影响易感宿主种群及感染性幼虫期尾蚴和囊蚴的存在。     

Epibionts of the red king crab Paralithodes camtschaticus (Tilesius, 1815) in Sayda Inlet of Kola Bay

The species composition of organisms associated with the red king crab Paralithodes camtschaticus (Tilesius, 1815) was investigated in Sayda Inlet of Kola Bay in 2004–2005. Nine fouler species and three symbiotic species were found on the carapaces of the red king crab. Balanus crenatus Bruigere 1789 barnacles were the most abundant fouler species and were found on 14.8% of the crabs. Symbiotic amphipods Ischyrocerus commensalis Chevreux, 1900 were found for one-tenth of all the crabs studied. The mean intensity of the amphipods was significantly greater for September, when the reproduction period of this species occurred. Male and female crabs were hosted with the same intensity. The number of host crabs increased accordingly to the crab size. The proportion of hosted crabs was three-fold less in Sayda Inlet than in the less polluted areas of the Barents Sea.     

Parasite modification of predator functional response

Parasite alteration of the host (predator) functional response provides a mechanism by which parasites can alter predator–prey population dynamics and stability. We tested the hypothesis that parasitic infection of a crab (Eurypanopeus depressus) by a rhizocephalan barnacle (Loxothylacus panopei) can modify the crab’s functional response to mussel (Brachidontes exustus) prey and investigated behavioral mechanisms behind a potential change in the response. Infection dramatically reduced mussel consumption by crabs across mussel densities, resulting in a decreased attack rate parameter and a nearly eightfold reduction in maximum consumption (i.e. the asymptote, or inverse of the handling time parameter) in a type II functional response model. To test whether increased handling time of infected crabs drove the decrease in maximum consumption rate, we independently measured handling time through observation. Infection had no effect on handling time and thus could not explain the reduction in consumption. Infection did, however, increase the time that it took crabs to begin handling prey after the start of the handling time experiment. Furthermore, crabs harboring relatively larger parasites remained inactive longer before making contact with prey. This behavioral modification likely contributed to the reduced mussel consumption of infected crabs. A field survey revealed that 20 % of crabs inhabiting oyster reefs at the study site (North Inlet estuary, Georgetown, South Carolina, USA) are infected by the barnacle parasite, indicating that parasite infection could have a substantial effect on the population level crab-mussel interaction.     

Phylogenetic ecology of gall crabs (Cryptochiridae) as associates of mushroom corals (Fungiidae)

Coral‐associated fauna is a relatively understudied topic. Hence, the nature of the relationship between an associated organism and its host is usually unknown. In the present study, the obligate associations between gall crabs (Decapoda: Cryptochiridae) and mushroom corals (Scleractinia: Fungiidae) are reviewed from a phylogenetic perspective. Based on field surveys, examination of museum material and a literature review, a total of 35 fungiid species have been found that act as hosts for four gall crab species. Fungiid‐associated gall crabs appear to be more geographically widespread than previously known, with new records showing their occurrences from the Red Sea and western Indian Ocean all the way to the central Pacific Ocean. The obligate nature of the association between cryptochirids and their hosts makes them an ideal model taxon to test for possible cospeciation events. The congruence between their phylogenies was tested by using the program Jane 4.0, resulting in cospeciation and duplication events between the crabs and their host corals. The sharing of several closely related host coral species by the same gall crab species or genus may provide support to models indicating phylogenetic relationships within the Scleractinia.     

Tyrosine hydroxylase protein expression in ventral nerve cord of Neotropical freshwater crab

Given the importance of catecholamines in coordinating physiological and behavioral responses in brachyurans, the present study was designed to investigate the distribution of tyrosine hydroxylase (TH)-positive cells and fibers in the ventral nerve cord of Dilocarcinus pagei the Neotropical freshwater crab. TH immunoreactivity was visualized in adult crabs of both sexes, during the intermolt period. We found TH-positive cells that have not been previously described in brachyurans. Specifically, we found a pair of TH-positive cells in the ventral region of the thoracic ganglion, and in ventral and dorsal regions of the abdominal (pleonic) ganglion, suggesting catecholaminergic modulation of claws’ function and abdominal structures. In addition, great population of TH-positive cells was observed in the subesophageal ganglion, indicating conservation during evolution of catecholamines in this ganglion of decapods. Dopamine is present in cells and fiber tracts of brachyuran ventral nerve cord, projecting to endocrine, cardiac and digestive structures, suggesting widespread modulation and control of physiological functions and behavior. Dopamine plays a central role in movement and psychiatric disorders in humans. Information on dopaminergic function in the nervous system of invertebrates should improve the understanding of its function in more complex systems, such as human beings.     

Microsporidia of the genera <Emphasis Type="Italic">Thelohania</Emphasis> (Thelohaniidae) and <Emphasis Type="Italic">Ameson</Emphasis> (Pereziidae) in two species of lithodid crabs from the Sea of Okhotsk

Diseases caused by microsporidia were found in the red king crab Paralithodes camtschaticus and the blue king crab P. platypus that inhabit the Sea of Okhotsk. Based on the histological features of the invasion and data on the morphological structure of the parasites, the microsporidia were assigned to the genera Thelohania and Ameson. Infected crabs exhibited severe destructive changes of their internal organs along with sharply pronounced external signs of disease. During the observation period, the microsporidian invasion was only found in females and young (unmarketable size) males from August to mid-October. Later, until mid-December, no diseased crabs were found.     

Quantifying the Effects of Green Crab Damage to Eelgrass Transplants

Mesocosm experiments were conducted in the summer of 1996 to quantify the effect of bioturbation by Carcinus maenas (the introduced European green crab) on survival of transplanted Zostera marina (eelgrass). The research grew out of a successful 2.52 ha eelgrass transplant project in the Great Bay Estuary of New Hampshire. At several subtidal sites, green crabs were found to damage transplanted eelgrass by cutting the shoots to the extent that some sites demonstrated poor survival. In three separate experiments, eight replicate mesocosm tanks were transplanted with 36 shoots of eelgrass, and different crab densities were introduced into the tanks. The number of shoots damaged by crabs was significantly higher in tanks with moderate (4.0 crabs/m²), high (7.0 crabs/m²), or very high (15.0 crabs/m²) crab densities than in tanks with low (1.0 crabs/m²) crab densities. Up to 39% of viable shoots were lost within one week of exposure to green crab activities. The mesocosm results demonstrated that green crabs were not directly attracted to eelgrass but that they significantly decreased transplant survival through their activity. Field densities of green crabs were found to exceed the density at which most damage occurred in the experiments, suggesting that this introduced species can be a major determinant of eelgrass transplant survival. The results underscore the major influence that biological components of transplant sites can have on transplant survival, and the need for their consideration in the site selection process.     

Study of epileptiform activity in cerebral ganglion of mud crab Scylla serrata

An attempt is made to induce in mud crab (Scylla serrata) epileptiform activities that resemble the generalized epileptic seizures. Cerebral ganglion of crab was exposed in situ, to a convulsant drug pentylenetetrazole (PTZ) 100 mM, for induction of seizures. Also, crabs were pretreated with antiepileptic drug viz sodium valproate (120 μmol/l) to inhibit epileptiform activities. The surface electrical discharges of cerebral ganglion were recorded using Unkelscope (MIT, USA) in control as well as experimental animals. The cerebral ganglion of crab showed a pattern of high cerebral electrical discharges after PTZ treatment compared to control. The sodium valproate promoted sedative action in control and prevented PTZ-mediated epileptiform discharges. Glutamate and GABA contents in cerebral ganglion were assayed. Glutamate level increased (31.45%) during PTZ treatment with concomitant decrease (43.93%) in GABA. Sodium valproate had no effect on glutamate concentration, but it decreased GABA by 24.75%. The present study shows that epileptiform activities can be induced in crabs.     

Detection and discovery of crustacean parasites in blue crabs (Callinectes sapidus) by using 18S rRNA gene-targeted denaturing high-performance liquid chromatography

Recently, we described a novel denaturing high-performance liquid chromatography (DHPLC) approach useful for initial detection and identification of crustacean parasites. Because this approach utilizes general primers targeted to conserved regions of the 18S rRNA gene, a priori genetic sequence information on eukaryotic parasites is not required. This distinction provides a significant advantage over specifically targeted PCR assays that do not allow for the detection of unknown or unsuspected parasites. However, initial field evaluations of the DHPLC assay suggested that because of PCR-biased amplification of dominant host genes it was not possible to detect relatively rare parasite genes in infected crab tissue. Here, we describe the use of a peptide nucleic acid (PNA) PCR hybridization blocking probe in association with DHPLC (PNA-PCR DHPLC) to overcome inherent PCR bias associated with amplification of rare target genes by use of generic primers. This approach was utilized to detect infection of blue crabs (Callinectes sapidus) by the parasitic dinoflagellate Hematodinium sp. Evaluation of 76 crabs caught in Wassaw Sound, GA, indicated a 97% correspondence between detection of the parasite by use of a specific PCR diagnostic assay and that by use of PNA-PCR DHPLC. During these studies, we discovered one crab with an association with a previously undescribed protist symbiont. Phylogenetic analysis of the amplified symbiont 18S rRNA gene indicated that it is most closely related to the free-living kinetoplastid parasite Procryptobia sorokini. To our knowledge, this is the first report of this parasite group in a decapod crab and of this organism exhibiting a presumably parasitic life history.     

Chemical host detection and differential attraction in a parasitic pea crab infecting two echinoids

Mechanisms of host detection and host choice are important for mobile parasites or symbionts that frequently move among host individuals. The parasitic pea crab Dissodactylus primitivus is an ectoparasite exploiting asymmetrically two spatangoid echinoid hosts, Meoma ventricosa and Plagiobrissus grandis. The entire life cycle takes place on M. ventricosa, while only adults colonize P. grandis, the host where female's fecundity is the greatest. Dissodactylus primitivus frequently exhibits host-switching, a behaviour that raises the question of host detection. To test if adult crabs are able to detect potential hosts and are attracted to the host where their fitness is greater, crab olfactory responses were investigated using a Y-tube. We first showed that D. primitivus are attracted by olfactory cues of M. ventricosa, versus those of a non-host echinoid species, Clypeaster rosaceus sharing the same habitat. This attractiveness was not due to a yellowish water-soluble substance secreted by the host. We then showed that the chemical attraction to the two hosts was different according to the origin of the crabs. Crabs coming from M. ventricosa were more attracted to this host than to P. grandis, a pattern compatible with an imprinting phenomenon. However, crabs collected from P. grandis were equally attracted to both host species, as if imprinting was lost after host change. We propose that the pattern of D. primitivus host detection could be intermediate between the behaviour of specialist and generalist symbionts.     

Black mat syndrome,an invasive mycotic disease of the tanner crab, Chionoecetes bairdi

Black mat syndrome, caused by an encrusting fungus on the exterior of the carapace of tanner crabs, has been known for many years. Although it is a nuisance when processing crabs for the commercial market, it has been thought to be restricted to the external surfaces of the crab and, therefore, nonpathogenic. In the present study, 11 tanner crabs from the Kodiak area of Alaska with and 9 without grossly recognizable masses of the fungus on the carapace were necropsied and examined histologically utilizing special stains selective for fungi. In all individuals with the syndrome, hyphae of the fungus, previously identified as Phoma fimeti, penetrated the carapace and virtually replaced the underlying epidermis. In the more advanced cases, the eyestalk was invaded and the epidermis destroyed, and hyphae extended into the eyestalk musculature and nervous tissue. To date, infections of the connective tissue sheaths surrounding the esophagus, stomach, heart, hemopoetic tissue, thoracic ganglion, antennal gland, and ovary have also been observed. None of the crabs without the syndrome contained internal hyphae. Although data on the lethality of the disease are not yet available, the ease with which the hyphae penetrate the chitinous exoskeleton, their extensive proliferation in the epidermis, and their ability to invade deep tissues causing obvious pathological effects, are highly suggestive that it is a virulent, probably fatal, disease that may have a significant impact on tanner crab population dynamics.