Hermit Crab Pagurus Longicarpus Say Research Articles

First record and spread of the long-wristed hermit crab Pagurus longicarpus Say, 1817 in the North Frisian Wadden Sea (Germany)

First record and spread of the long-wristed hermit crab Pagurus longicarpus Say, 1817 in the North Frisian Wadden Sea (Germany)

Utilization of partially predated snail shells by the hermit crab Pagurus longicarpus Say, 1817

The hermit crab Pagurus longicarpus was shown to inhabit shells that were partially predated from intertidal areas of Long Island, New York. Among field collections of P. longicarpus, 2.13% of the hermit crabs (46 of 2155) were found with shells with snail tissue present. Over 90% of these partially predated snail shells were occupied by male hermit crabs. Although hermit crabs were in 8 species of snail shells, only Littorina littorea and Nassarius obsoletus were found occupied by hermit crabs and containing snail tissue. In the laboratory, we found that specimens of the spider crab Libinia emarginata were able to pull off the operculum of snails, leaving damage as found in field collections. In contrast, specimens of P. longicarpus were not able to prey on live, healthy snails. When specimens of P. longicarpus were placed in communal tanks, hermit crabs preferred partially predated snail shells to empty and original shells. However, original shells and empty shells were occupied with more frequency than partially predated shells when crabs were isolated. These findings indicate P. longicarpus actively seeks shells soon after attack and abandonment by snail predators, especially in the presence of competitors.

Morphological and genetic evidence for vicariance and refugium in Atlantic and Gulf of Mexico populations of the hermit crab Pagurus longicarpus

The number and wide variety of southeastern United States marine taxa with significant differentiation between Gulf of Mexico and Atlantic Ocean populations suggests that these taxa may have experienced major vicariance events, whereby populations were subdivided by geological or ecological barriers. The present study compared variation in morphology, allozymes, and mtDNA in Gulf of Mexico and western Atlantic populations of the longwrist hermit crab Pagurus longicarpus Say collected during 1997 and 1998. Combined Atlantic populations had significantly fewer denticles on the second segment of the third maxilliped than did Gulf of Mexico populations, and the mean ratio of dactyl length to propodus length was significantly greater in the Atlantic crabs than in the Gulf of Mexico crabs. Allozyme allele frequencies at three loci showed genetic differentiation between a Gulf of Mexico population and two Atlantic populations. Analysis of mtDNA sequence data revealed a clear reciprocal monophyly between Gulf and Atlantic populations, with an estimated divergence age of ~0.6 million years ago. This estimated age of divergence is significantly more recent than an age previously estimated for its congener Pagurus pollicaris (~4 million years ago), suggesting that species with a similar genetic break between Gulf and Atlantic populations may not necessarily share an identical history. Surprisingly, there is evidence of geographic subdivision within Atlantic populations of P. longicarpus along the east coast of North America. This differentiation is especially strong between Nova Scotia and southern populations, suggesting that the Nova Scotia population may represent survivors from a northern refugium during the last glacial maximum.

Prevalence of Two Epicaridean Isopods (Bopyridae and Entoniscidae) Associated with the Hermit Crab Pagurus longicarpus Say, 1817 (Anomura) from the New Jersey Coast (U.S.A.)

The epicaridean isopods Stegophryxus hyptius and Paguritherium alatum, parasitic in the hermit crab Pagurus longicarpus, are reported for the first time in New Jersey waters. Fourteen of 9,111 crabs (0.15%) were infested with the ectoparasitic S. hyptius, and 4 of 3,703 crabs (0.11%) were infected with the hemocoel-dwelling P. alatum. Crabs of both sexes were parasitized by each species. Prevalences of S. hyptius and P. alatum were considerably lower than those recorded over 50 yr ago in the Woods Hole region of Massachusetts.

Feeding Behavior of Dipolydora commensalis (Polychaeta: Spionidae): Particle Capture, Transport, and Selection

Feeding Behavior of Dipolydora commensalis (Polychaeta: Spionidae): Particle Capture, Transport, and Selection

Association of the Hermit Crab Pagurus Longicarpus Say, 1817, With Symbiotic Hydroids: Consequences of Predation By Lobsters

Previous studies indicate that symbiotic hydroids of the genus Hydractinia protect hermit crabs from certain predators, but have little effect on others. Laboratory experiments were performed to elucidate the relationship between the long-clawed hermit crab, Pagurus longicarpus, and its symbiotic hydroid, Hydractinia symbiolongicarpus, in environments with and without a predator, the lobster Homarus americanus. Hydroids did not protect P. longicarpus from predation by H. americanus. P. longicarpus escaped predation by burrowing into the sand or fleeing. The presence of H. americanus had no effect on the preference of P. longicarpus for hydroid-covered shells, further supporting the hypothesis that H. symbiolongicarpus does not protect P. longicarpus from predation by H. americanus. Overall, P. longicarpus showed no preference for shells with or without hydroids, suggesting that the costs of associating with hydroids roughly equal the benefits.

Association of the Hermit Crab Pagurus Longicarpus Say, 1817, With Symbiotic Hydroids: Consequences of Predation By Lobsters

Association of the Hermit Crab Pagurus Longicarpus Say, 1817, With Symbiotic Hydroids: Consequences of Predation By Lobsters

Symbiotic organisms increase the vulnerability of a hermit crab to predation

The association between the hermit crab Pagurus longicarpus Say and an ectosymbiotic colonial hydroid of the genus Hydractinia was studied to determine whether the presence of Hydractinia affects the resistance of Pagurus longicarpus to predation. Observations of tethered hermit crabs confirmed the importance of predation by the blue crab, Callinectes sapidus Rathbun, on the Pagurus longicarpus population in Nantucket Harbor, Massachusetts. In a predation experiment, caged hermit crabs in Littorina littorea (L.) shells with and without Hydractinia were exposed to single blue crabs. Shell damage indicated that blue crabs attacked hermit crabs in both shell types in roughly equal proportions: 65% of hermit crabs in shells with Hydractinia were attacked compared to 69% of hermit crabs in shells without Hydractinia. Only 20% of hermit crabs in shells with the hydroid survived attack, however, compared to 54% in shells without Hydractinia. Continuous observation of predation in aquaria showed that hermit crabs in shells with Hydractinia had significantly shorter survival times when attacked by a blue crab than hermit crabs in shells without the colonial hydroid. The crushing resistance of shells was measured with an Instron™ testing machine. A comparison of the regression equations of shell mass (g) vs. crushing resistance (N) between shell types showed that shells with Hydractinia had a lower slope than shells without Hydractinia, although because of a wide range in crushing resistance, this difference was not significant. Shells with Polydoran worm burrows, however, were significantly weaker than shells without burrows, and shells with Hydractinia were more likely to hold worms than shells without Hydractinia. The positive correlation between Hydractinia and shell-degrading worms explains the vulnerability of hermit crabs in shells with the colonial hydroid to predation by blue crabs. Other studies have shown that hermit crabs may benefit from having Hydractinia on their shells because the hydroid prevents large and potentially harmful ectosymbionts, such as Crepidula species, from colonizing. Thus, for Pagurus longicarpus the costs and benefits of the association with Hydractinia may change depending upon the presence of other organisms and this may shift the nature of the association with Hydractinia from mutualism to commensalism to parasitism

The effects of shell availability on intraspecific competition in experimental populations of the hermit crab, Pagurus longicarpus Say

It has been proposed in the literature that intraspecific competition in hermit crabs, mediated by a succession of shell exchanges, would lead to members of a given size class experiencing approximately the same level of shell adequacy. This hypothesis was modified and extended to predict that intraspecific competition should result in the maximization of the correlation between hermit crab size and shell size, regardless of the level of shell adequacy. The prediction has been tested by establishing laboratory populations of the hermit crab Pagurus longicarpus Say, and simulating these populations using a computer program which assumed constant motivational states and dominance relationships. The populations at the beginning of the experiment consisted of 19–21 individuals inhabiting shells as a result of a process that did not allow actual shell selection. The populations were divided among three treatments based on the availability of 0, 10, or 20 shells in addition to those inhabited initially. At the end of the first week, all populations displayed an increased correlation between hermit crab weight and shell weight, and these values were similar to those generated by the computer simulation. The values at the end of the second week, however, showed a noticeable decline in the populations with no empty shells available. In addition, these populations had the largest number of injuries, which could only be the result of aggressive encounters between hermit crabs. The results of these experiments are used to formulate a general model of hermit crab behavior under different levels of shell availability and shell adequacy.

The effect of temperature on osmotic responses of the hermit crab Pagurus longicarpus say

1. 1. Groups of six hermit crabs with shells, Pagurus longicarpus Say, were exposed to one of 30 different temperature-salinity conditions. 2. 2. At low temperatures of 2 and 6°C, the osmolarity of the blood of the hermit crabs was isosmotic to the medium, while at higher temperatures of 10, 14 and 18 C, the osmolarity of the blood ranged from 200–450 mOsm/1 above that of the medium at most salinities. 3. 3. We hypothesize that at the higher temperatures, the hermit crabs sustained metabolic rates high enough to support hyperosmotic regulation while at the lower temperatures they did not. 4. 4. Low temperature-low salinity conditions were most stressful as evidenced by high mortality, swelling and motor impairment.

The effects of gastropod shell availability and habitat characteristics on shell utilization by the intertidal hermit crab Pagurus longicarpus Say

The shell utilization patterns of two intertidal populations of the hermit crab, Pagurus longicarpus Say, were studied. The populations differed with respect to the physical characteristics of their habitats and the availability of empty gastropod shells. The first population was in an estuary connected to Narragansett Bay. This population had few, if any. empty shells available in the area. The second population was in a rock-cobble area directly on Block Island Sound. There were large numbers of empty gastropod shells available for this population. The consistently high gastropod mortality on this shore appears to be caused by the animals being washed up on the beach, where they die due to desiccation. Data from samples collected from June to November of both 1974 and 1975 showed that there were distinct differences in the shell utilization patterns of the two populations. A greater proportion of the animals collected from the estuary population inhabited damaged shells and/or shells with symbionts compared to the individuals from the population with large numbers of empty shells available. The results of shell selection experiments indicated that individuals from both populations inhabited less than preferred shells. The population with large numbers of empty shells available was qualitatively shell-limited because of the effect of physical factors on the morphology of the gastropod species of that area. In addition, the shell selection experiments showed that individuals from the two areas had significantly different shell preferences. This result may be explained by the effects of the environment on the growth rates of the hermit crabs and/or as an indication that shell preferences may vary in response to the physical factors of a given habitat.

The Effect of Parasitism by an Entoniscid on the Secondary Sex Characters of Pagurus longicarpus

The common hermit crab Pagurus longicarpus Say is parasitized at Woods Hole by two species of EPICARIDEA (a suborder of isopod crustaceans). A bopyrid, Stegophryxus hyptius Thompson, occurs attached to the abdomen and an entoniscid, Paguritherium alatum Reinhard, is found within the haemocoele. Simultaneous parasitism by both the bopyrid and the entoniscid is, however, of rare occurrence. Stegophryxus causes no external modifications of the host, neither does it effect any marked reduction of the gonads. Paguritherium, on the other hand, brings about complete castration of female hosts and more or less complete atrophy of the male gonads. The pleopods of infested males are unmodified, but those of infested female crabs, while normal in number, resemble the male type more than they do the type characteristic of normal adult females. The effects of RHIZOCEPHALA and EPICARIDEA on the secondary sex characters of hermit crabs as reported in the literature fall into four categories: I. Male pleopods modified; female pleopods unaffected. By RHIZOCEPHALA: Pagurus cuanenis (Nilsson-Cantell, 1926) and Pagurus prideauxii' (Potts, 1906; Baffoni, 1947). By EPICARIDEA: Pagurus bernhardus (Giard, 1887; Bonnier, 1900) and Pagurus prideauxii (Baffoni, 1947). II. Male and female pleopods both modified. By RHIZOCEPHALA: Pagurus meticulosus (Potts, 1906) and Pagurus samuelis (Shiino, 1931). III. Male pleopods unaffected; female pleopods modified. By RHIZOCEPHALA: Pagurus bernhardus (Giard, 1887; Guerin-Ganivet, 1911). IV. Male and female pleopods both unaffected. By RHIZOCEPHALA: Anapagurus chiroacanthus (Nilsson-Cantell, 1926) ; Pagurus pubescens (Reinhard, 1942). By EPICARIDEA: Pagurus longicarpus (Thompson, 1901). No case has been reported in which a female pagurid manifested alterations in its secondary sex characters under the influence of an epicaridean parasite and only a few instances, based on scarce material, where the presence of a rhizocephalan parasite affected the external characters of the female alone. It was therefore thought worth while to study the female pagurids infested with Paguritherium and analyze as completely as possible the modifications of the pleopods with respect to the size of the host, the amount of deviation from the normal and the precise nature of the changes to discover whether the alterations were a retention of the juvenile condition, a state of female intersexuality, or some other phenomenon.

EXPERIMENTS ON THE DETERMINATION AND DIFFERENTIATION OF SEX IN THE BOPYRID STEGOPHRYXUS HYPTIUS THOMPSON

Stegophryxus hyptius Thompson, an ectoparasite on the abdomen of the hermit crab Pagurus longicarpus Say, seeks the definitive host as a cryptoniscus larva.The free-swimming cryptonisci are sexually undifferentiated and sexually undetermined. Differentiation follows fixation and is dependent on environmental factors. These conclusions are justified on the basis of the following observations and experiments.1. Cryptonisci that settle directly on the host develop into females; those that attach to a female bopyrid develop into males.2. Changes in the color pattern of the cryptonisci following fixation furnish criteria for judging the length of time they have been subjected to a particular environment.3. Histological examination of the cryptoniscus shows that the gonads are not yet present as recognizable structures.4. Presumptive female cryptonisci, if removed from the host at an early age and transferred to the brood pouch of a female Stegophryxus, will transform into males.5. The failure of the converse e...