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.     

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.     

Unaltered hematocrit values and differential hemocyte counts in acanthocephalan-infected Armadillidium vulgare

Three cell types were present in Armadillidium vulgare hemolymph. Hyaline cells, 8.2 to 12.0 μm in size with a few fine granules in the cytoplasm, comprised 42% of the cells. Twelve percent of the cells were nonexplosive granulocytes, 8.8 to 15.0 μm, with many cytoplasmic granules of medium size. A third cell type, an explosive 7.2- to 12.0-μm granulocyte with coarse cytoplasmic granules, comprised 46% of the cells. Within 48 hr after adult specimens of A. vulgare were fed eggs of the acanthocephalan, Plagiorhynchus cylindraceus, isopod hemocytes aggregated in the intestinal epithelium surrounding penetrating acanthors. Encapsulation and death of the parasite routinely followed. No significant difference in hematocrit values or in differential hemocyte counts occurred between infected and uninfected control isopods.     

Lobster (Homarus americanus) hemocytes: Classification,differential counts,and associated agglutinin activity

Four hemocyte types were recognized in the lobster based on size and refractile nature of the granules, the ratios of cytoplasm to nucleus, and Giemsa stain characteristics. Two hyaline types were designated as prohyalocytes (1.8%) and hyalocytes (64.2%), and two granular types were termed eosinophilic granulocytes (12.2%) and chromophobic granulocytes (21.9%). There was no significant difference in the percentages of the different hemocyte types (differential hemocyte counts) between sexes, but hyalocyte and eosinophilic granulocyte percentages varied significantly between populations of lobsters. The data suggested that the difference in agglutinin activity (HA) between lobsters with the same total hemocyte numbers was due to activity associated with fixed hemocytes or quantitative differences in HA activity associated with one or more hemocyte types, rather than an increase in the percentage of any one particular type in circulation.     

Hemocyte reactions and early cellular changes during melanotic tumor formation in Drosophila melanogaster

In Drosophila melanogaster tu bw larvae melanotic tumors form as a result of a cell-mediated immune response involving the encapsulation and melanization by hemocytes of portions of the caudal adipose tissue. The tissue-specific encapsulation response is not due to the disintegration of the basement membrane surrounding the adipose tissue as is reported to be the case in other melanotic mutants. Prior to encapsulation large numbers of hemocytes appear in the circulation and begin to differentiate into flattened cells termed lamellocytes. This transformation occurs at a time when changes are noted within the adipose cells. The localized accumulation of blood cells near intact basement membrane suggests that abnormally developing adipose cells acquire altered molecular surfaces or release substances to which the hemocytes respond. The initial reaction of the hemocytes with the adipose tissue is cell lysis, and this is rapidly followed by the aggregation of numerous additional blood cells which eventually cohere to one another to form a multilayered capsule. What little evidence there is of disintegration of the basement membrane occurs only after hemocytes have lysed at the surface, and other blood cells begin to invade the adipose tissue. Melanization occurs first in the intercellular spaces along the plasma membranes of the lysed cells, and progresses from the innermost layers toward the periphery of the encapsulating cells. Since the changes observed in the hemocytes and adipose cells are precocious, occurring to a lesser degree later in normal development, the initial effect of the genetic mutation in tu bw larvae may be an endocrine dysfunction which causes an asynchronous and abnormal development of the caudal adipose tissue and/or the hematopoietic organs.     

Influence of temperature on the zoeal development and elemental composition of the cancrid crab, Cancer setosus Molina, 1782 from Pacific South America

Temperature changes during ENSO cause mass mortalities of adult Cancer setosus, but the effects on early life stages are unknown. The influence of temperature on survival, development and biochemical composition was studied in larvae of the hairy crab, C. setosus, from a population off the northern Chilean coast. In rearing experiments conducted at four different temperatures (12, 16, 20, 22 °C), zoeal development was only completed at 16 and 20 °C, after 78 and 36 days, respectively. Instar duration was negatively correlated with temperature. A multiple linear model relating larval body mass (in carbon) to temperature and developmental time suggests that successful larval development is possible within a narrow temperature range only. The biochemical composition, measured as carbon, hydrogen, and nitrogen (C, H, N) content, show in general the typical oscillating changes during the moult cycle of brachyuran crab larvae. However, at high (22 °C) and low (16 °C) temperatures, CHN values show deviations from the typical pattern, indicating threshold temperatures for larval activity and survival. These findings indicate that the larval development of C. setosus is compromised under conditions of El Niño, with temperatures exceeding the upper thermal temperature tolerance threshold of larvae. Effects of El Niño on early life history stages and recruitment rates should be increasingly taken into account in fisheries management strategies.     

Biological features of a puzzling symbiotic association between the hermit crab Dardanus insignis and the porcellanid crab Porcellana Sayana (Crustacea)

The symbiotic lifestyle is widespread among porcellanid crabs, which maintain ecological and co-evolutionary associations with annelid polychaetes, poriferans, cnidarians, echinoderms, gastropod mollusks, and other crustaceans such as shrimps and hermit crabs, among others. We investigated the ecological association between the hermit crab Dardanus insignis and the porcellanid Porcellana sayana, in southeastern Brazil. Porcellanid crabs, hermit crabs, and available shells were collected monthly from July 2001 to June 2003, with a shrimp boat equipped with two double-rig trawl nets. The majority of P. sayana specimens were collected in shells occupied by D. insignis (96.6%); a few were found in empty shells (3.4%). The catch of both symbionts and hosts increased with increasing depth, with the highest occurrence at 35 m. The P. sayana crabs of various sizes could be found solitary or forming aggregations of up to 14 individuals per host, showing no sex or size segregation. In spite of the high diversity of shell species occupied by the hermit crabs and also available in the field, only a few of them were also utilized by P. sayana. The majority (93%) of shells utilized by P. sayana also hosted other symbiont species, constituting the basis of extensive symbiotic complexes. Thus, the ecological relationship between D. insignis and P. sayana may be classified as a non-obligate and non-specific symbiosis that may also involve other facultative organisms such as sea anemones.     

Spatial overlap and interaction between sub-adult American lobsters, Homarus americanus, and the invasive European green crab Carcinus maenas

Invasive species are considered one of the major threats to biological diversity, and they can negatively impact species of particular ecological and/or economic importance. In this study, we investigate the potential threat that the European green crab, Carcinus maenas, represents to sub-adult lobsters, Homarus americanus, in Passamaquoddy Bay, Canada, northwest Atlantic. We conducted transect surveys using SCUBA diving to evaluate spatial overlap between these species inside, and immediately adjacent to, a lobster nursery area, and ran two laboratory experiments to investigate interactions between them in conditions of limited food and shelter availability. We found marked spatial overlap between these species in nature, particularly between adult green crabs and sub-adult lobsters in the shallower parts of the nursery area. It was not uncommon to see green crabs and sub-adult lobsters less than 1-2 m from one another, and we estimated mean nearest-neighbor values as low as 0.5-1 m on certain transects and months, with a grand mean of 5.17 ± 1.62 m (SE). Monte Carlo randomization of positional data revealed that green crabs and lobsters were randomly distributed relative to one another; individuals of one species did not seem to aggregate or segregate relative to individuals of the other species. In the lab, green crabs did not negatively affect survival (one exception), growth, activity, feeding, or shelter use of sub-adult lobsters. In fact, sub-adult lobsters regularly preyed upon green crabs in the first lab experiment, where heterospecific individuals were matched for body mass. Our results suggest that green crabs do not pose a significant threat to sub-adult lobsters in Passamaquoddy Bay, and may in fact represent a food subsidy for them.     

Cellular defense reactions of the shore crab, Carcinus maenas: in vivo hemocytic and histopathological responses to injected bacteria

The cellular defense reactions of the shore crab, Carcinus maenas, were studied, following injections of the bacteria Bacillus cereus and Moraxella sp., by histological and ultrastructural examination of the gills, heart, and hepatopancreas. The majority of the bacteria were sequestered to the gills, but some were also later evident in the heart and hepatopancreas. The presence of the bacteria in the gills initiated the formation of numerous small cell clumps, composed of both refractile and phagocytic cells, which entrapped many microorganisms. The clumps reached a maximum size 6 hr after inoculation and although some were cleared from the gills others persisted for 7 days, becoming more compact and necrotic during this period. Clump formation appears to occur following recognition of the bacteria as foreign and results in the hemocytes becoming sticky and adherent. The response is very effective in rapidly immobilizing the bacteria, thus restraining the spread of infection. It is proposed that this phenomenon may be a significant component of crustacean cellular host defenses.     

Virus particles in an internal parasite, Portunion conformis (Crustacea: Isopoda: Entoniscidae), and its marine crab host, Hemigrapsus oregonensis

Based on morphological evidence and preliminary physicochemical data, we report the first picornavirus from crustacean hosts. The viral particles are widespread in the tissues of an isopodan parasitic castrator, Portunion conformis, and its shore crab host, Hemigrapsus oregonensis, collected in San Francisco Bay, California. Less frequently, infected cells of the parasitic isopod also contain larger viral particles.     

Ion fluxes and diffusion potentials in the Dungeness crab,Cancer magister

Summary Transepithelial potentials (TEP's) were measured in Dungeness crabs exposed to a variety of experimental media. The TEP's can be accounted for as diffusion potentials. In sea water (SW) theP _Na/P _Cl ratio (calculated by substitution in the Goldman equation) was 0.68, but in dilutions of SW the value increased, reaching a maximum of 3.33 in freshwater (FW). When the calcium and magnesium concentrations in the diluted media were maintained at SW levels theP _Na/P _Cl remained close to that in SW.The effluxes of Na and Cl were monitored in crabs exposed to the experimental media and the TEP's were measured simultaneously. After transfer from SW to FW the decrease in Na efflux was considerably less than expected from the change in potential alone, indicating an increased permeability to sodium, while transfer from SW to 500 mM NaCl caused a 3.4-fold increase in Na efflux without any associated change of potential. These results indicate an increase in the permeability of the gill epithelium to Na as the ambient concentrations of Ca and Mg decline. The Cl effluxes are not dependent on the external concentration of divalent ions, but about 30% of the Cl efflux may be due to exchange diffusion.Abbreviations FW freshwater - SW sea water - TEP transepithelial potential This project was in part supported by faculty research grants from Fordham University, Bronx, NY and Towson State University, Towson, MD to GDR     

Cytological observations on the blood and hemopoietic tissue in the crab,Callinectes sapidus

Summary A fine structural analysis of hemocytes recovered from the pericardial sinus of the blue crab (Callinectes sapidus) demonstrates that hyaline cells, intermediate cells, and granuloyctes are present in the hemolymph. A detailed consideration of their shared and differing cytological features suggests that the various blood cells represent different stages of cytogenesis along a common or single path of cellular differentiation. The potential functional complexity of the hemocytes is attested to by the occurrence within their cytoplasm of three and/or possibly four morphologically distinct types of inclusion bodies, and other membrane-bounded compartments (e.g., lysosome-like structures, autophagic vacuoles, peroxisome-like bodies) whose function is unknown. Preliminary examination of the well-developed Golgi organelle in the intermediate cells and granulocytes indicates its probable participation in the elaboration of the inclusion bodies; however, the details of its role in granulogenesis and in the known plurifunctional capacities of these cells remain obscure.I wish to thank Dr. Phyllis T. Johnson for her interest and advice during the course of this investigation and Ms. Jane T. Wade for her assistance in preparing the specimens for ultrastructural observation     

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.     

Detrimental effects of Ulva lactuca (L.) exudates and low oxygen on estuarine crab larvae

Conventional theory postulates that associations between marine macrophytes and animals are generally positive. This paper presents evidence, however, that a common species of green macroalga, Ulva lactuca (L.), is detrimental to estuarine invertebrates due to the production of toxic exudates and low oxygen tensions which occur in the seaweed beds at night. Bioassays of the responses of zoeae of five species of estuarine crabs (Callinectes sapidus Rathbun, Carcinus maenas L., Eurypanopeus depressus Smith, Neopanope texana savi Smith and Rhithropanopeus harissii Gould), using water in which Ulva lactuca was cultured for 24 h, produced 100% mortality after 22 days. No crabs survived the molt into megalopa. Hypoxic water, 0.5 ± 0.3 ppm oxygen, caused a decline in larval activity (movement), but there was no mortality over an 8-h period, Ulva-water purged to 0.4 ± 0.1 ppm oxygen caused 100% mortality in 13–40 min. These synergistic effects could be critical in estuaries where dense U. lactuca beds cause periods of low dissolved oxygen. We hypothesize larval recruitment may be limited in such systems, particularly in areas where flushing is poor.     

Pathological changes in the nephrocytes of the shore crab, Carcinus maenas, following injection of bacteria

The gills of Carcinus maenas were examined by light and electron microscopy following injection of either sterile saline or the bacteria Bacillus cereus and Moraxella sp., to determine any role(s) for the nephrocytes in the host defense reactions. The results showed that although intact bacteria were not sequestered to the nephrocytes, these cells were active in the removal of large quantities of cell debris from the hemolymph. Much of this material was derived from the breakdown of the hemocytes in response to the presence of bacteria and it's accumulation in the central vacuoles of the nephrocytes resulted in the degradation of these cells. It is proposed that while nephrocytes do not phagocytose intact bacteria, they augment the host defenses by clearing much of the hemocyte and associated bacterial debris from the gills, thus preventing blockage of the lamellar sinuses and subsequent impairment of respiration.     

Patterns of larval release in the Florida stone crab, Menippe mercenaria

Larval release patterns in brachyuran crabs are often synchronized with environmental cycles. While previous studies have focused extensively on supratidal and intertidal taxa, there have been relatively few investigations of subtidal species. This study examined patterns of larval release by the Florida stone crab, Menippe mercenaria, from three different tidal regimes. Ovigerous stone crabs were collected from Sebastian Inlet on the east coast of Florida, Tampa Bay on the west coast of Florida, and the Florida Keys. Patterns of larval release were monitored in the laboratory in relation to local tidal and diel cycles. Results showed a significant diel pattern in initiation of hatching by crabs from each of three study areas. Larval release consistently occurred during the diurnal phase despite the maintenance of females in constant laboratory conditions for up to 96 h prior to hatching. This implies that release may be controlled by a circadian clock. Patterns of release by stone crabs in relation to tidal cycle were more variable. Larval release by females from populations near Tampa Bay and Sebastian Inlet were not synchronized with the tides, whereas females collected from the Florida Keys exhibited a pattern that was strongly related to tidal cycle. These results may be explained by differences in tidal amplitude at the three sampling locations.     

Bioenergetics of early life-history stages of the brachyuran crab Cancer setosus in response to changes in temperature

In many marine invertebrates, a latitudinal cline in egg size is considered an adaptive response to a decrease in temperature, and enhances the energetic fitness of their larvae at hatching. However, the amount of energy carried over from the egg to the larval stage depends on the metabolic efficiency of egg development. In the present study, eggs of the brachyuran crab Cancer setosus were sampled for their dry mass (DM), carbon (C), nitrogen (N), and fatty acid (FA) content throughout development from blastula stage until hatching of zoea 1-larvae at Antofagasta (23°S) and Puerto Montt 41°S (Chile) under different temperature treatments (12, 16 and 19 °C). Hatching zoea 1 larvae contained 60 ± 3% of the initial blastula egg C content, regardless of site or temperature. However, the ontogenetic decrease in egg C content was to a significantly higher extend based on the utilization of energy-rich FA at 12 °C (− 1.16 µg/egg) compared to the 19 °C treatments in Antofagasta and Puerto Montt (− 0.63 to − 0.73 µg FA per egg). At 19 °C egg-metabolism was based to a substantial extend on protein, which allowed for the saving of energy-richer lipids. We conclude that the production of larger eggs with high FA content appears to be adaptive not only to fuel the larval development, but is also a response to the prolonged egg developmental times at lower temperatures.     

Endogenous rhythms of locomotion in the American horseshoe crab, Limulus polyphemus

American horseshoe crabs (Limulus polyphemus) exhibit clear circadian rhythms of visual sensitivity in the laboratory and in the field they exhibit seasonal patterns of mating behavior that are closely associated with the tides. Recent reports suggest that Limulus locomotor activity may be controlled by endogenous circadian and/or circatidal clocks and that light:dark (LD) cycles may affect the rhythmic output of both of these clocks. In this study, we examined locomotor behavior in the laboratory to determine the extent of this endogenous activity and to examine the influence of LD cycles on these rhythms. Thirty-three L. polyphemus were captured during the breeding season and their activity was monitored with activity boxes and “running wheels” in seawater kept at constant temperature and salinity. Activity patterns were analyzed using visual inspection of actograms and Chi-square and Lomb-Scargle periodograms. Overall, 36% of the animals was significantly more active during L, while only 12% was more active during D (52% showed no preference). Circatidal rhythms were observed in LD in 67% of the horseshoe crabs. Surprisingly, LD cycles appeared to synchronize these rhythms at times. In DD, the majority of animals tested (63%) exhibited circatidal rhythms that persisted for at least seven days. Overall, the results demonstrate that an endogenously controlled tidal rhythm of locomotion operates during, and significantly after, the breeding season in this species. In addition, the present results are consistent with the presence of circalunidian oscillators controlling these rhythms.