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Some ecological aspects of the land hermit crab Coenobita scaevola (Coenobitidae) at Wadi El-Gemal protected area, Red Sea
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The terrestrial hermit crab Coenobita compressus appears to detect and approach aggregations of conspecifics. Since this hermit crab tends to form clusters surrounding a food item, an individual approaching an aggregation will often discover a desirable piece of food. This study provides quantitative field evidence for the use of social facilitation in foraging by C. compressus.
Annual migrations and spawning for the common land hermit crab, Coenobita clypeatus in Playa Sardinera and possibly in Uvero, Mona Island, occur in August or early September. Spawning corresponds to the crescent moon in the lunar cycle.
Shell selection by the hermit crab, Pagurus pollicaris (Say), was studied in a natural population and in laboratory experiments. The results indicate that hermit crabs vary their preference for shells of a certain weight and volume, depending upon the species of shell. When the weight of the shell was increased ≈25%, either by its natural epifauna or artificially, hermit crabs continued to occupy shells of the same size and volume, suggesting that shell volume was more important than weight in shell selection.Alterations of the angle of the shell axis and position of the shell's center of gravity often resulted in an aversion to the altered shells by both P. pollicaris and P. longicarpus (Say), indicating that variations in these two shell properties may influence shell selection. These results provide evidence that hermit crabs select shells on the basis of several shell traits that bear on the protection offered by the shell or by the ease with which it can be carried.
The reproductive ecology of three sympatric hermit crab species from the Bay of Panama is examined. All three species reveal patterns of size and reproduction mediated by their supply of shells. Shells are demonstrated to be in limited supply. Crabs with shells large enough to allow growth, put effort into growth at the expense of reducing reproductive expenditures, while crabs in shells too small to permit growth allocate more time and effort into immediate reproductive gains. This resource regulated trade-off between growth and reproduction gives these tropical crabs plasticity in important life-history traits. Crabs with a relatively poor supply of shells reproduce at smaller sizes, reproduce more frequently, have larger clutches, and are unable to reach the larger sizes of crabs with a less limiting supply of shells. This flexibility in life-history traits allows these crabs to tailor their reproductive schedules to resource supplies controlled by gastropod mortality, as well as the presence of competitors and predators.
Gastropod shell availability and utilization by the hermit crab Pagurus brevidactylus (Stimpson, 1859) at Anchieta Island, Brazil, were determined as part of a long-term effort to understand the dynamics of hermit crab shell utilization. All shells occupied by these hermits, found empty, or with live gastropods were collected monthly, from JanuaryDecember 2000, by SCUBA divers. A total of 3704 gastropod shells of 32 species was collected (1528 were occupied by crabs, 1943 had live gastropods, and 233 were empty). Shells of two of the four most common gastropod species in the field [Cerithium atratum (Born, 1778) and Morula nodulosa (C. B. Adams, 1845)] were also the most occupied by P. brevidactylus. The morphometric relationships that best describe the association between hermits and their shells were those involving the dimensions of the crabs and shell internal volume and dry weight. The shell occupation pattern of P. brevidactylus is correlated with shell availability in the field, although the hermits also have the capacity to select shells according to their dimensions.
Terrestrial hermit crabs (Coenobita compressus (H. Milne Edwards)) on Isabel island, México, prefer Nerita (Ritena) scabricosta (Lanark 1822) over other species of shells. Nerita scabricosta, the lightest species of shell, has the highest internal volume/weight ratio (IV/W ratio) of all species available at the island. Heavier shells (low IV/W ratio) are more costly to carry and may restrain growth. We hypothesized that crabs will search for shells with high IV/W ratios to save energy, and predicted that in every individual shell-exchange crabs will prefer a shell with a higher IV/W ratio. Observations of spontaneous aggressive shell-exchange interactions in nature between crabs carrying preferred shells (with high IV/W ratio) and crabs using less preferred species of shells (low IV/W ratio) support this idea. By inducing individual shell exchanges in the field, we experimentally confirmed the preference for shells with high IV/W ratio, and we also showed that crabs prefer larger shells over those they were bearing. Moving to a larger but not heavier shell may facilitate growth though saving energy that would otherwise be spent in locomotion. High growth rates seem to be advantageous because size is a correlate of fertility, since large males apparently have more access to females, and large females produce larger clutches, thus indicating the possible reproductive benefits for preferred light and large shells.
We conducted a study in order to determine the shell utilization pattern of the land hermit crab Coenobita scaevola (Forskäl, 1775), the only species representing the family Coenobitidae in the Red Sea. Hermit crabs were collected during July 2003 and January 2004 along the sandy shores of protected area of Wadi-Elgemal, south Red Sea. Animals were fixed in 10% for-malin and transported to the laboratory where they were weighed and measured for cephalothoracic shield length (CSL) and width, left propodus length and height. Gastropod shells species were identified, weighed and measured for shell aperture width and length and shell internal volume. A total of 391 individuals were collected (219 females, 172 males) and were found occupying ten shell species, with clear significant occupation of Nerita undata. A positive relationship was obtained between the size of the shells occupied and the hermit crabs. Analysis of shell internal volume and crab dimensions demonstrated that this shell dimension con-stitutes mainly the determinant for C. scaevola shell utilization. With respect to the size of the animals and the occupied shell type, Nerita undata was occupied by a wide range of CSL (2.5–8.5mm). Small sized crabs (2.5–3.5mm CSL) occupied Planaxis sulcatus and Nassarius arcularius plicatus while larger specimens (8.5–9.5mm CSL) occupied Turbo radiatus, Polinices milanostomus and Monodonta canilifera. Variations in the shell occupation were also recognized among male and females. Comparisons among pop-ulational and shell use features led us to suggest the use of this land hermit crab as key-species in the preserving program of shores and protected areas, since this species is the first organism to disappear from any shore when a new tourist establishment is imple-mented.
Pagurus longicarpus hermit crabs depend on empty gastropod shells for protection against predation. Hermit crabs avoid gastropod shells in which holes have been drilled by naticid gastropods, and hermit crabs forced to occupy drilled shells are more vulnerable to predation by green crabs, Carcinus maenas. In this study, we examined the effect of predator cues on P. longicarpus shell investigation behavior and shell choice. In paired laboratory shell choice trials, we examined hermit crab response to green crab chemical cues. We compared hermit crabs from two sites differing in the percentage of
Littorina littorea shells with drill holes. The percentage of time hermit crabs spent occupying intact shells increased significantly in the presence of predator cues. The effect of predator cues on the amount of time hermit crabs spent investigating shells differed between individuals from the two sites. Predator effluent had a marginal effect on the proportion of hermit crabs initially choosing intact shells and within 15min most hermit crabs in both treatments occupied intact shells due to shell switching. These results indicate that predation cues alter P. longicarpus shell choice behavior favoring intact shells, which provide greater protection. In summary, predation appears to be a key factor influencing hermit crab shell selection behavior.
Land hermit crabs are scavengers that use olfaction to locate their foods. Although they are scavengers, land hermit crabs do not select their foods randomly. This study demonstrates that land hermit crabs (Coenobita compressus H. Milne Edwards) display negative preference induction when feeding on natural foods, preferring foods that they have not experienced recently. These induced feeding preferences were measured at a population level by recording crab choices among food odors in the field with olfactory attraction assays. When the abundances of foods in their habitat were altered, crabs preferred the odors of foods that were less abundant. Induced feeding preferences were measured at an individual level by recording crab choices among 3 foods in a laboratory choice assay. Crabs more frequently chose foods that they had not experienced during the previous 24 h. As a consequence of this behavior, land hermit crabs consume a broader diet, which may result in crabs obtaining a more nutritionally balanced diet or limiting their exposure to toxins.
In southern Atlantic studies on hermit crab biology are scanty considering the local biodiversity. In this way, some population features of Paguristes calliopsis Forest and Saint Laurent, 1968 such as size frequency distribution, sex ratio and shell occupation in the natural environment were studied. Specimens were collected by means of scuba methods in the infralittoral area of the Anchieta Island. A total of 116 individuals were analyzed. Size measurements (minimum; maximum; mean shield length +/- sd, respectively) were 0.8; 4.5; 2.76 +/- 0.79 mm for males and 2.28 +/- 0.36 mm for females. The sex ratio was 1.47:1 in favor of males which prevailed in the largest size classes. The hermit crabs occupied shells from eleven gastropod species and Cerithium atratum (Born 1778) was significantly the most occupied one (75.86%). Significant correlations were not obtained in all regression analysis, demonstrating sexual differences on fitting of the occupied shells. In the studied area P. calliopsis population is small if compared with the other hermit crab populations. The shell utilization varies as a function of shell availability and hermit crabs interspecific competition, in relation to the other coexistent species.
Gilchrist, S.L. 2003. Hermit crab population ecology on a shallow coral reef (Bailey’s Cay, Roatan, Honduras): octopus predation and hermit crab shell use. In: Lemaitre, R., and Tudge, C.C. (eds), Biology of the Anomura. Proceedings of a symposium at the Fifth International Crustacean Congress, Melbourne, Australia, 9‐13 July 2001. Memoirs of Museum Victoria 60(1): 35‐44. Shells can be a limiting factor in allowing hermit crab populations to increase. Predators of gastropod molluscs and of hermit crabs release shells into reef environments where hermit crabs find and cycle them within their populations. Predators also play a role in distributing shells among hermit crab species. To highlight how octopuses influence shell availability to hermit crabs, observations were made on members of Octopus vulgaris Cuvier, 1797 and O. briareus Robson, 1929 at Bailey’s Cay Reef (Roatan, Honduras) during July and August each of three years, 1999‐2001. In addition to feeding while foraging, Octopus vulgaris and O. briareus individuals create shell and debris middens outside of their temporary dens. These middens concentrate shells and food for hermit crabs in the reef environment where locating an empty shell could be difficult. However, because hermit crabs are prey items for octopuses, hermit crabs using the middens risk predation from the den occupant. Relatively small hermit crab species such as Pagurus brevidactylus (Stimpson, 1858) and P. criniticornis (Dana, 1852) were found commonly in dens and among middens, opening the possibility that the den functions as a refugium for some species as well.
Casual observation of several Octopus species suggested that the modification of the habitat involved in construction of sheltering dens might attract other animal species, sometimes called "den associates." A study comparing the presence of motile epibenthos in areas around dens of Octopus cyanea with nearby control areas quantified this assumption. One species group, juvenile Scaergus parrotfish, was significantly less likely to be found around O. cyanea dens, possibly because den construction disrupted growth of algae on which the parrotfish fed. Two species, the wrasse Thalassoma duperry Quoy & Gaimard, 1824, and the hermit crab Calcinus latens Randall, 1839, were more likely to be found at dens of O. cyanea. Both species appeared to be scavenging on the remains of prey left by octopuses, and their presence thus appeared to indicate an opportunistic but loose association.
The movements of individual Coenobita clypeatus were tracked in a mark-recapture study for one month on the island of Cayos Cochinos, located off the Atlantic coast of Honduras. Of the 346 crabs marked along the study transect, which extended along an elevational gradient from 20 to 125 meters, 25 were recaptured once and 4 individuals were recaptured on more than one occasion. Crabs traveled at a mean rate of 22 meters/day (SD=30). Large crabs did not travel significantly faster than smaller crabs. There was no relationship between crab size and position along the elevational gradient.
The objective of this study was to characterize the pattern of shell utilization by Paguristes tortugae, from infralittoral areas of Anchieta Island (Ubatuba, Sāo Paulo State, Brazil) using the percentage of the different shell types occupied and the morphometric relationship between hermit crabs and occupied shells. Specimens were collected monthly (January to December 1998) by SCUBA diving. The animals and the shells were measured and weighed. A total of 2,429 hermit crabs were captured occupying 21 species of gastropod shells. The shells more occupied were Pisania auritula (35.49%), Cerithium atratum (27.83%), Morula nodulosa (12.70%) and Leucozonia nassa (6.83%), respectively. There was differential shell occupation between sexes: males and ovigerous females occupied in higher percentage P. auritula shells while the non-ovigerous females occupied C. atratum. Regression analysis showed best correlation between the size of the crabs (shield length) and shell dry weight. This study showed that shell occupation by P. tortugae involves inter- and intraspecific competition as well as shell type availability in the field.
McLaughlin, P.A. 2003. Illustrated keys to families and genera of the superfamily Paguroidea (Crustacea: Decapoda: Anomura), with diagnoses of genera of Paguridae. In: Lemaitre, R., and Tudge, C.C. (eds), Biology of the Anomura. Proceedings of a symposium at the Fifth International Crustacean Congress, Melbourne, Australia, 9‐13 July 2001. Memoirs of Museum Victoria 60(1): 111‐144. Keys, with illustrations of selected diagnostic characters, are provided for the seven families and 122 genera of the anomuran Superfamily Paguroidea, commonly known as hermit crabs and king crabs. In addition, abbreviated diagnoses are presented for the 69 genera presently assigned to the family Paguridae.
The population of the hermit crab Calcinus tibicen in the Ubatuba region was studied with emphasis on seasonal abundance, seasonal size-frequency distribution, sex-ratio, and reproductive period based on the percentage of ovigerous females. The animals were collected at 2-month intervals for 2 consecutive years (from January 1993 to November 1994). Total mean animal size in shield length was 5.14 ± 1.23 mm for males, 4.23 ± 0.79 mm for females, and 4.53 ± 0.60 for ovigerous females. A discontinuity in reproduction was observed, with an absence of ovigerous females in July (winter) and a high incidence from September to May (spring to autumn). Calcinus tibicen is sexually dimorphic in relation to size, with a higher growth rate in males. The sex-ratio pattern changes with season, indicating that it is more a function of season or habitat than of size.
Certain aspects of the behavioral ecology of the tropical hermit crab, Calibanarius abidigitus, can be analyzed more fully with the use of fitness set theory. Building on the premise that an optimum shell weight/body weight ratio (termed @'weight index@') confers maximum fitness to individual crabs, two independent estimates of fitness, clutch size and percentage aggressive dominance, were plotted against a wide range of weight indexes. These measures were made for individuals of C. albidigitus inhabiting two environments (represented as two species of gastropod shells) and behavioral and reproductive fitness sets were constructed. The dissimilarities of the predicted optimum weight indexes for the two fitness sets, combined with the fact that suitable gastropod shell present a limiting resource, indicate a behavioral strategy by which larger shells than necessary for maximum reproductive fitness are utilized. This strategy, termed the "optimal ratios strategy," has definite advantages to individual hermit crabs and has probably evolved in response to severe competition for shells.
Field studies have suggested that the intertidal hermit crabs of the San Juan Islands of Washington normally occupy snail shells smaller than preferred. In this study the effects of shell size on protection from predation and on hermit crab shell fighting were studied in the laboratory. A predator (Cancer) presented with two hermit crabs (Pagurus granosimanus), identical except in size of occupied shell, preyed upon the hermit in the smaller shell first in 15 out of 16 trials. This results suggests that large shell size confers a selective advantage on the occupying crab. Shell fights involving two hermit crabs (P. hirsutiusculus) of unequal size were observed in which replicates differed only in the shell size of the larger crab. The probability of the larger crab effecting a shell exchange through fighting was shown to increase as the size of its shell decreased. However, shell size was shown to have no effect on the level of aggressiveness as measured by four criteria. The mechanism underlying the former result thus appears to involve a continual high level of general aggressiveness together with an increased tendency associated with occupancy of an inadequate shell by the dominant crab for that crab to evoke a shell exchange during an aggressive interaction.
The availability of gastropod shells to hermit crabs in the Newport River Estuary, Beaufort, N.C. has been assessed by determining the numbers of usuable shells occurring in characteristic subtidal habitats and by measuring shell size adequacy. The proportion of useable shells occupied by hermit crabs ranged from 58–99 % and many of the shells not used by hermit crabs were judged unavailable because they were occupied by sipunculids or only uncovered by the dredge. The shell adequacy index (shell size occupied/shell size preferred) was significantly below 1.0 for the largest species (Pagurus pollicaris Say) in the one location where sufficient numbers were collected and for the next largest species (P. longicarpus Say) in three of the four locations where it was collected. The shell size adequacy index for the smallest species (P. annulipes Stimpson) did not differ significantly from 1.0 in either of the two locations in which it was found. These observations suggest that the availability of gastropod shells plays a significant rôle in limiting the abundance of at least the larger hermit crabs.
Hermit crabs are ever alert for more suitable shells to inhabit, but what this may mean for coastal shell middens has rarely been considered. Here, the impact of the most landward-based of hermit crab families, the tropical Coenobitidae, upon archaeological shell-bearing deposits is assessed using a case-study: the Neolithic Ugaga site from Fiji. At Ugaga, hermit crabs were found to have removed the majority of shells from the midden and had deposited their old, worn shells in return. The behavioural ecology of genus Coenobita suggests a mutualistic interaction whereby humans make available shell and food resources to hermit crabs, which in turn provide a site cleaning service by consuming human and domestic waste. Diagnostic indicators of terrestrial hermit crab wear patterns on gastropod shells are outlined and the conditions under which extensive ‘hermitting’ of shell midden deposits may occur are investigated. The ability to recognise hermit crab modification of shells is considered not only important for archaeomalacologists analysing tropical shell deposits, but also for field archaeologists wishing to select suitable shell samples for radiocarbon dating.
The use of gastropod shells by hermit crabs at Quirimba Island, Mozambique, was investigated. Particular attention was paid to the upper shore/supralittoral zone species Clibanarius longitarsus, Coenobita cavipes and Coenobita rugosus. The study area is characterised by a high diversity of gastropod species as well as hermit crabs. Supralittoral hermit crabs were lithe, if at all, resource restricted due to concentration of empty shells on the strandline and shell middens created by local people. The range of the 3 study species overlaps substantially and each uses a wide range of shell types. Shore habitat, shell abundance and availability were found to have little influence on shell use. With increased tidal emersion/terrestrial nature (for a given crab mass), total diversity of shells used increased, shell mass carried decreased, damaged shell use decreased and carried shell fit increased. The architecture and strength of shells used, however, followed more complex individual species characteristics and behaviour patterns. Species specific differences in behavioural patterns may be important for shell resource partitioning.
A diverse assemblage of 16 species of hermit crabs occurs on the shores of the Quirimba Archipelago, northern Mozambique. Each species illustrated marked zonation such that they formed a distinct sequence from the subtidal across the wide intertidal zone to the supra-littoral. In addition to shore height zonation, there was distinct variation in type and range of habitat preferences. Of the 5 study islands, Quirimba and Quisiva had the greatest intertidal habitat variety and the largest number of resident hermit crab species. The number of hermit crab species peaked at 10 in the lower-shore zone and decreased upshore to 3 supra-littoral species and downshore to 8 subtidal species. In contrast, the density of hermit crab individuals peaked in the upper mid-shore, at 3 m(-2). The mid-shore zone was also the primary region of cluster formation, principally involving Clibanarius laevimanus and Clibanarius virescens, although 3 other species were also involved. The activity of the 2 semi-terrestrial species, Coenobita rugosus and Coenobita cavipes, on Quirimba Island was principally related to the light:dark cycle but was strikingly different between open and mangrove habitats. Some degree of activity took place in both species throughout a 24 h period in the mangrove habitat, where the peak of feeding activity was twice that of the open sand scrub habitat. Wind strength was a major influence on the activity of C. rugosus and C, cavipes, reducing the number of active individuals to zero at higher wind speeds, even in thinly mangroved habitats.
Gastropod shells serve as a portable shelter for hermit crabs and provide protection for their otherwise vulnerable, soft abdomens. This study investigates the effect of prior shell experience and water flow on hermit crab shell selection. Research at Bodega Bay, California, examined shell selection in Pagurus granosimanus (Stimpson) and Pagurus samuelis (Stimpson) as a function of previous shell occupancy. Laboratory experiments found that when Pagurus granosimanus was presented two weight-matched shells of Olivella biplicata (Sowerby) and Tegula funebralis (Adams), it was significantly more likely to choose the shell species that it was collected in. Survey data yielded different shell use patterns between Pagurus granosimanus and Pagurussamuelis, with Pagurus samuelis using almost exclusively Tegula funebralis and Pagurus granosimanus using Olivella biplicata and Tegula funebralis at one site while using Tegula brunnea (Philippi) at another site. It was also found that Pagurus granosimanus is found deeper in the intertidal than Pagurus samuelis. Research conducted on Mo'orea, French Polynesia, examined the effect of water flow on shell selection by hermit crabs. Population surveys and laboratory experiments were combined to determine if Calcinus seurati (Forest) from high flow and low flow environments select shells of different weight. It was found that Calcinus seurati collected from a high flow site selected significantly heavier shells than those collected from the still water site. Laboratory experiments also showed a tendency for Calcinus seurati to select heavier shells in a high flow treatment than in a no flow treatment. Reef crest populations of Calcinus gaimardii (Edwards) and Calcinus elegans (Edwards) were also surveyed and compared with Calcinus seurati survey data. A significant difference in shell weight was found between Calcinus gaimardii and Calcinus seurati from the still water site. No other significant differences were found among species. Regression analyses indicate a correlation between hermit crab weight and shell weight for all three Mo'orean species.
Shell preferences, as shown by laboratory choice experiments, are important determinants of shell utilization under natural conditions. Size and shell species preferences of the hermit crab Calcinus tibicen were determined for the three most occupied [Stramonita haemastoma (Linnaeus, 1767), Leucozonia nassa (Gmelin, 1791) and Pisania auritula (Link, 1807)] shell species along the rocky shore of Grande beach, Ubatuba, Brazil, taking into account the sexual condition of the individuals. All experiments were conducted under laboratory conditions using a glass aquarium where the hermit crabs (independent on their sex condition) were placed naked with a large number of shells of appropriate sizes. The chosen shells were determined after 72 h. The preferred shell species and size were determined by regression analysis. C. tibicen showed no significant choice among the three gastropod shell species. Shell size experiments revealed that the preference of hermit crabs was strongly associated with shell weight and internal volume. The shell adequacy index (SAI) decreased with increasing crab size and showed that the population was occupying relatively adequate shells (SAI=0.99±0.19). The present data lead us to conclude that shell selection by hermit crabs involves individual and sexual preferences taking into account the shell features that best provide protection and survival, principally in the rocky intertidal studied area, characterized by intense wave action.
The shell selection behaviour of Coenobita scaevola Forskal has been examined in a natural population by statistical methods and by selection experiments using shells whose weights had been artificially changed. In a natural population of C. scaevola there was a definite weight index (weightof the shell/weight of the animal) for the shells of each species of snail. The weight index for one population ranged between 0.7 and 13.0, with a maximum (46% of all values) between 1.3 and 1.9. The volume index (volume of the shell/weight of the animal) ranged from 0.7 to 4.0. The maximum (59%) for the shells of all snail species lay between 1.0–1.3. Small specimens of C. scaevola tolerate greater differences in the weight and volume indexes of their host shells than large specimens.
Coenobita clypeatus, the purple-clawed (terrestrial) hermit crab, almost exclusively uses the extinct shells (fossil and subfossil) of the West Indian topshell, Cittarium pica in Bermuda. These coenobitid crustaceans were found to: 1) taphonomically modify the Cittarium shells, and (2) cause temporal reworking of the extinct shells within a modern community. Fossil shells inhabited by these crabs had extreme apertural modifications. Additionally, almost all shells possessed a drag mark region. Using these taphonomic criteria, one-third (18%) of in situ (collected) Pleistocene shells from Bermuda were once-occupied by Pleistocene hermits. These findings elucidate, in part, the enigma of why a large marine shell (Cittarium) is present in back-beach, dune and paleosol deposits in the Pleistocene of Bermuda. -from Author
The occurrence of empty gastropod shells and those occupied by the hermit crab, Pagurus bernhardus, was examined on the shore. This survey suggested that small crabs prefer L. littoralis shells to those of Gibbula species and this was confirmed by preference tests in the laboratory. Crabs removed from these small shells show an initial preference for Nucella shells to those of L. littorea. However, medium sized crabs collected in either Nucella or L. littorea prefer the species in which they were collected. This preference is still apparent when the size of the test shells is varied. These data provide the first clear evidence for a modification of shell preferences after experience of particular shell species.
—Male gonopores on most hermit crabs (Paguroidea) occur as circular or oval ap- ertures on the coxae of the fifth pereopods, are flush with the surrounding coxal segment, may be covered by a membrane or a calcified operculum, and are normally associated with numerous com- plex setae. In many male paguroids of the fami- Ues Paguridae and Coenobitidae, elongate tube- like extensions called sexual tubes are found on the coxae. The sexual tubes of C. perlatus and C. clypeatus of the Coenobitidae are here investigat- ed at the histological and SEM level for the first time. Coenobita clypeatus has two short, squarish, equal/subequal extensions of the coxae with the densely hirsute gonopore directed ventrally. In contrast, C. perlatus has large, unequal, tubular extensions of the coxae, directed posteriorly, and with the hirsute gonopores terminally on the tubes. The right sexual tube is the longest, and curves across the mid-line of the body. The left sexual tube is much shorter and extends posteri- orly from the coxa. In both, the sexual tubes have various coarse setae of several different morpho- types. Histological sectioning reveals a vas defer- ens terminating at the gonopore, and that sexual tubes are as heavily calcified and muscular as the coxal segments they emanate from. This differs markedly from previously investigated sexual tubes in other paguroids.
The population of Paguristes
erythrops (Crustacea: Anomura) was studied based on seasonal abundance, size–frequency distribution, sex ratio and reproductive period (percentage of ovigerous females). Specimens were collected monthly by SCUBA diving in the infralittoral area of Anchieta Island, Ubatuba. A total of 543 individuals was analysed. Animal size (minimum and maximum shield length, respectively) was 1·7 and 11·8 mm for males, 1·7 and 10·3 mm for non-ovigerous females, and 3·2 and 7·8 mm for ovigerous females. The sex ratio was 0·91:1. Sexual dimorphism was recorded by the presence of males in the largest size-classes. The absence of ovigerous females during winter months (June to August) and their high incidence from January to March indicated discontinuity in the reproductive cycle, suggesting that females become ovigerous and breed in the summer, with the spawning period lasting from spring to autumn. This strategy of reproduction probably was based on competition with other coexisting species in this area.
Two populations of Clibanariuserythropus from Mediterranean and Atlantic rocky shores were studied to provide data on morphometry, population structure and shell use under different environmental contexts. Hermit crab sex and size were analysed as well as genus, dimension and status of the inhabited shells. A comparison between the two populations gave particular emphasis to the morphological and eco-ethological plasticity of this hermit species.
There is a complex interrelationship between upper shore hermit crabs (such as Coenobita sp. and Clibanarius sp.), coastal human populations and mangrove forests in Mozambique. The abundance, activity, shell selection and behaviour of three species of hermit crab are related to the level of mangrove cover. With increased density of mangrove trees, the study species of hermit crab changed in abundance, tended to become diurnal, spent more time feeding and were clustered in larger groups when doing so, and selected longer spired shells. All five of the same variables are also linked to the proximity and activity of humans through both direct and indirect actions. Direct effects included a tendency to nocturnal activity with proximity to human activity; indirect effects included increased and more clumped food supplies, and shell middens from intertidal harvesting and deforestation. Mangroves are important to local human populations as well as to hermit crabs, for a wide variety of (similar) reasons. Mangroves provide storm shelter, fisheries and fishery nursery grounds for adjacent human settlements, but they also harbour mosquito populations and their removal provides valuable building materials and fuel. Hermit crabs may be useful (indirectly) to coastal human populations by being a source of food to certain commercial species, and by quickly consuming rotting/discarded food and faeces (thereby reducing disease and pests). They can also cause minor problems to coastal human populations because they use shells of (fisheries) target mollusc species and can be more abundant than the living molluscs, thereby slowing down effective hand collection through confusion over identification. The mixture of positive and negative attributes that the three groups impart to each other in the Quirimba Archipelago, northern Mozambique, is discussed.
Juvenile Octopus vulgaris foraged by chemotactile exploration, mainly in crevices and under rocks. They caught small crustaceans and molluscs, including Lima bivalves, and preferred crabs and Lima in a simple laboratory choice test. Octopuses consumed 30% of their prey away from home, and small remains of prey deposited in the midden were selectively removed by waves and currents resulting in an underestimate of the octopus' intake and diet.
Several factors potentially influencing predation rates on the hermit crab Pagurus longicarpus (Say)_ were investigated near northeastern Gulf of Mexico salt marshes. Relative predation rates for hermit crabs in different shell types were measured at four tidal levels at four sites using tethering techniques. Predation differed between sites, but not between tidal levels at most sites. Shell species, shell size, and shell damage also had no influence on predation rates. Limited trammel netting indicated that several species of hermit crab predators were common across the intertidal zone. In the laboratory, hermit crabs that were allowed to bury fell prey to striped burrfish Chilomycterus schoepfii (Walbaum) significantly less frequently than hermit crabs that could not. P. longicarpus may depend more on behavioral adaptations such as burying, rather than qualities of the shell shelter, to evade the array of predators in this habitat.
Many mobile animals migrate because of the different benefits provided by different localities in time and space. For hermit crabs, such benefits include resource (shell, water, food) acquisition and gamete release. One of the more successful crustacean land-invaders, Coenobita hermit crabs, undertake complex short-range migrations in SW Madagascar. Number of active hermit crabs was inversely related to wind strength and positively related to tidal range, emphasising that movement would conserve water. A circadian component was also recorded in the locomotory activity of Coenobita pseudorugosus and C. rugosus. Path linearity varied with many of the same parameters, but also with beach slope. Movement was primarily perpendicular to shore in small individuals, but the parallel proportion increased with hermit crab size and tidal range, probably driven mostly by shell and food searching. Despite the costs of movement and shell carriage in the terrestrial environment, C. pseudorugosus and C. rugosus were as fast as their marine counterparts. Their speeds varied principally with individual size and were approximately 20% faster without shells and about 20% slower when climbing up a 20 slope, compared to horizontal or downhill travel. Hermit crabs, which are highly numerous and speciose in SW Madagascar, do not seem to partition niches by differential movement patterns. Aside from provision of shells in middens and capturing large adults for bait or pets, human activity may have a profound effect on hermit crab movement: observations at rare uninhabited marine reserves like Nosy Ve show that considerable diurnal activity may take place despite the apparent hostility of the environment to an essentially marine animal.
The population of the hermit crab Diogenes pugilator is numerically quite substantial in the examined area, therefore it is analysed if the population was subject to any pressure by predators and by other species of hermit crabs living in that zone. It was found there is a potential pressure by predators which might influence it. Only Liocarcinus depurator is able to keep the population trend of D. pugilator under control. With regard to the relationships with the other species of hermit crab, D. pugilator dominates only over Pagurus anachoretus, while in the other cases, there was just competition for food.
Most hermit crabs have a specialized lifestyle that requires them to occupy gastropod shells. The size of shells that hermit crabs inhabit relative to their body size affects their growth, survival and fecundity. In this study, the effects of shell fit on individual growth rate, risk of predation, feeding rate, and activity level were examined in the laboratory for hermit crabs Pagurus longicarpus collected from Nahant, MA, USA. Feeding rate and general activity level of hermit crabs confined to tightly fitting shells and hermit crabs occupying shells of preferred size were not significantly different. Hermit crabs confined to tightly fitting shells grew at significantly slower rates, and were significantly more susceptible to predation by a common North Atlantic rock crab, Cancer irroratus. While this study provides further evidence of the negative effects of tight shell fit on growth and survivorship of hermit crabs, a mechanistic explanation for the decreased growth rate of hermit crabs in tightly fitting shells is still sought.
The responses of Australian hermit crabs to two types of shell-related odor cues were compared. Introduction of gastropod snail odor elicited an increase in grasping of shells in all four species tested ( Clibanarius infraspinatus, C. taeniatus, C. virescens , and Diogenes avarus ). However, the magnitude of response in the case of C. virescens was significantly lower than the responses of individuals of the other species. Individuals of C. infraspinatus responded to introduction of conspecific hemolymph with an increase in both locomotion and the frequency of grasping of shells. C. infraspinatus also responded to the hemolymph of the other three species, and there were no differences in the magnitude of the responses depending upon the source of the hemolymph. When individuals of C. infraspinatus were exposed to snail odor and conspecific hemolymph at the same time, the responses were indistinguishable from those shown to hemolymph alone. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/44892/1/10886_2005_Article_BF02029549.pdf
Interspecific competition is often difficult to measure due to the lack of a definitive limiting factor for the two (or more) species. The gastropod shell inhabited by a hermit crab represents a very discrete, definable portion of the ecological needs of every animal. A hermit crab must have protection for its soft abdomen or it will rather quickly be eaten. In addition, the ritualized shell fighting behavior patterns of hermit crabs (Hazlett, 1966a, 1966b, 1967) offer an easily observed specific behavioral parameter which reflects the extent of interspecific vs. intraspecific competition for this ecological factor.
Shell of the adult hermit crab has some important roles for its fitness. In the same time, the shell size often limits the body growth of its owner. To grow the body size larger, the individual must change the shell to another larger shell. If the individual cannot get another larger one, the individual has to suppress the body size growth as the occupied shell size allows. Growth suppression would result in the lower fitness. With a simple mathematical model, we consider the criterion about whether the individual should try to change the shell or not in order to get the higher fitness. We show that the optimality of a shell change behavior has a relation with the body size and the season length for the shell change. They also affect the optimal timing for the shell change. It is implied that the probability of the success in a shell change and the cost for the shell change behavior do not affect the optimal timing for the shell change at all but significantly do the optimality of the behavioral choice.
Distribution and assemblages of anomuran crustaceans in
- A Fransozo
- F L Mantelatto
- G Bertini
- Fernandes-Goes L
- J M Martinelli
Fransozo A, Mantelatto FL, Bertini G, Fernandes-Goes L and Martinelli JM. (1998). Distribution
and assemblages of anomuran crustaceans in Ubatuba Bay, north coast of São Paulo State,
Brazil. Act. Biol. Ven., 18: 17-25.
Gastropod shell availability as a potential resource for the hermit crab infralittoral fauna of Anchieta Island (SP)
- A L Meireles
- R Biagi
- F L Mantelatto
Meireles AL, Biagi R and Mantelatto FL (2003). Gastropod shell availability as a potential
resource for the hermit crab infralittoral fauna of Anchieta Island (SP), Brazil. Naup., 11(2):
99-105.
Seashells of the Egyptian Red Sea. The illustrated Handbook. The American Uni
- M L Rusmore-Villaume
Rusmore-Villaume, M.L. (2008). Seashells of the Egyptian Red Sea. The illustrated Handbook.
The American Uni. in Cairo Press Cairo, New York. 307pp.