The influence of some symbionts on the shell-selection behaviour of the hermit crabs, Pagurus pollicarus and Pagurus longicarpus

The influence of some symbionts on the shell-selection by the hermit crabs Pagurus pollicarus and P. longicarpus was examined by placing individual hermit crabs with two similar shells in a choice situation and recording the shell occupied after 12 hr. One shell contained a symbiont species and the other did not. The results indicated that organisms normally found on or in empty shells influence the shell-section by these species of hermit crab. P. pollicarus preferred shells occupied by the sea anemone Calliactis tricolor or by the hydroid Hydractina echinata as opposed to bare shells. P. longicarpus also preferred shells with H. echinata. Both crab species rejected shells with the barnacle Balanus amphitrite. Shells containing the molluscs Crepidula fornicata or C. plana were rejected by the smaller hermit crab P. longicarpus. These molluscs appeared to exert no influence on P. pollicarpus unless they were large or abundant, at which point their weight or occlusion of available space possibly has negative effects on the crab.     

Hermit crab biocoenoses: a worldwide review of the diversity and natural history of hermit crab associates

The symbiotic associates of hermit crabs (excluding parasites and flora) are reviewed worldwide. The review includes species found on the shells occupied by hermit crabs (epibiotic species), species boring into these shells (endolithic species), species living within the lumen of the shell (either free-living or attached to the shell), species attached to the hermit crabs themselves, and hypersymbionts. In total over 550 invertebrates, from 16 phyla are found associated with over 180 species of hermit crabs. Among these associates, 114 appear to be obligate commensals of hermit crabs, 215 are facultative commensals, and 232 are incidental associates. The taxa exhibiting the highest number of associates are arthropods (126), polychaetes (105), and cnidarians (100). The communities of species associated with Dardanus arrosor, Paguristes eremita, Pagurus bernhardus, Pagurus cuanensis, and Pagurus longicarpus are the best studied and harbor the most diverse assemblages of species. While trends in biodiversity of hermit crab assemblages do not follow predicted patterns (e.g., hermit crabs within the Indo-West Pacific do not harbor more species than those from temperate regions), this is suggested to reflect a lack of sampling rather than a true representation of the number of associates. Hermit crabs date to at least the Cretaceous and provided a niche for a number of groups (e.g., hydractinians, bryozoans, polydorids), which were already associates of living gastropods. Apparently hermit crab shells initially supplied a substrate for settlement and then these symbiotic relationships were reinforced by enhanced feeding of symbionts through the activity of the hosts. Through their use and recycling of gastropods shells, hermit crabs are important allogenic ecosystem engineers in marine habitats from the intertidal to the deep sea. Hermit crabs benefit from some symbionts, particularly cnidarians and bryozoans, through extension of shell apertures (alleviating need to switch into new shells) and by providing protection from predators. However, hermit crabs are also negatively impacted (e.g., decreased reproductive success, increased predation) by some symbionts and a review of egg predators is provided. Thus, the symbiotic relationships between hermit crabs and many associates are difficult to characterize and often exhibit temporal changes depending on environmental and biological factors. Research on the biology of these symbionts and the costs/benefits of their associations with hermit crabs are analyzed. While some associates (e.g., Hydractinia spp.) have been studied in considerable detail, for most associations little is known in terms of the impacts of symbionts on hosts, and future experimental studies on the multitude of relationships are suggested.     

Reproductive costs of the symbiotic hydroid Hydractinia symbiolongicarpus (Buss and Yund) to its host hermit crab Pagurus longicarpus (Say)

Studies on the interaction between the hermit crab Pagurus longicarpus and its symbiotic hydroid Hydractinia symbiolongicarpus have focused on positive effects of hydroids on their host hermit crabs (e.g., protection from predators). Yet, these benefits may be balanced with reproductive costs, which are rarely studied. Results from field observations, laboratory trials, and a mesocosm experiment indicate that female hermit crabs in hydroid-colonized shells exhibit depressed ovigery, smaller clutch sizes, and increased clutch failure relative to females in bare shells. Frequent switching between bare and hydroid-colonized shells may alleviate negative effects when the density of hydroids in the environment is low, but at high densities Hydractinia may significantly impact hermit crab reproduction.     

Sex-specific differences and the role of predation in the interaction between the hermit crab, Pagurus longicarpus, and its epibiont, Hydractinia symbiolongicarpus

The interaction between the hermit crab, Pagurus longicarpus, and the shell epibiont, Hydractinia symbiolongicarpus, varies from mutualism to parasitism based on the environmental context. We tested the hypothesis that this interaction also varies as a function of hermit crab sex. Given that recent work showed a negative effect of Hydractinia on female reproduction, we predicted a greater frequency of males in Hydractinia shells in the field and a stronger preference by males than females for shells with Hydractinia. Field collections documented a significantly greater proportion of males than females occupying shells with Hydractinia, and a significantly greater proportion of ovigerous females than non-ovigerous females in shells with Hydractinia. In laboratory shell-switching experiments, a greater proportion of males than females chose to enter shells with Hydractinia, but there was no difference in the proportions of males and females that vacated shells with Hydractinia.We examined whether the presence of Hydractinia influenced predation rates. Blue crabs fed on more than twice as many hermit crabs in shells with Hydractinia as compared to bare shells, but there was no significant difference for stone crabs. Laboratory experiments showed that the force required to crush shells was significantly greater for shells without Hydractinia. Thus, the lower occupancy and preference exhibited by females than males for shells with Hydractinia appears to result both from the decreased reproduction shown in past studies and an increase in predation risk.     

Predation on symbiont sea anemones by their host hermit crab Dardanus pedunculatus

Feeding by host hermit crabs Dardanus pedunculatus on their symbiotic sea anemones Calliactis polypus was investigated using animals collected at Shirahama, Wakayama Prefecture, Japan. In the first experiment, changes in the number of sea anemones on hermit crab shells were recorded in single‐and double‐crab trials without food and single‐crab trials with food. The number of sea anemones significantly decreased under starved conditions. The extent of this decrease per single hermit crab was higher in the double‐crab trials than in the single‐crab trials. Direct observations and video recordings showed that hermit crabs occasionally removed sea anemones from their own shells, and also from partners’ shells in the double‐crab trials, and consumed them. In the second experiment, fed and unfed hermit crabs with or without sea anemones were examined for body weight changes. Fed hermit crabs gained weight whereas unfed hermit crabs lost it. The degree of weight loss in unfed hermit crabs was significantly higher in those without sea anemones, which indicates some value of the latter as food. We offer some speculations on the course of development of this symbiosis, with predation on sea anemones having played an important initial role.     

Shell shape affects movement patterns and microhabitat distribution in the hermit crabs Calcinus elegans, C. laevimanus and C. latens

This study examined the influence of shell shape on the distribution and movement patterns of three species of Hawaiian hermit crabs: Calcinus elegans, C. laevimanus, and C. latens. Field surveys showed strong differences in shell use depending on habitat. Individuals of C.elegans and C. latens were more frequently in unusual shapes of shells (the cowrie Cypraea caputserpentis and the variable worm shell Serpulorbis variabilis) when in tide pools and in more standard gastropod shells, such as the dog whelk Nassarius papillosus, when found in the subtidal. In addition, for both C.elegans and C. latens in tide pools, most crabs in unusual shaped shells were out on top of rocks, whereas most crabs in shells that were standard shapes were under rocks.In the laboratory, individuals of C.elegans and C. laevimanus in unusual shells initiated more shell exchanges and when given empty shells crabs readily occupied the standard shaped shells, but crabs did not move into the unusual shaped shells. Mark-recapture experiments in the field showed that C. elegans in standard shaped shells moved out of tide pools and stayed longer when placed on subtidal coral heads, whereas crabs in unusual shaped shells stayed in tide pools and did not stay on subtidal coral heads (in part due to predation). Laboratory tests showed that C. elegans in unusual shaped shells were more readily dislodged by surge than crabs in standard shaped shells. Thus, the difference in movement patterns in preferred vs. unpreferred shell shapes is an important factor influencing the microhabitat distribution of these hermit crabs.     

Effect of gastropod shell characteristics and hermit crabs on shell Epifauna

The epifauna on gastropod shells occupied by the hermit crabs Pagurus pollicaris (Say) and P. longicarpus (Say) was examined, as was the utilization of shells by these two hermit crabs. In the study area in Tampa Bay, Florida, shells were not a limiting factor to the hermit crab population, and there apparently was little competition for shells. Interspecific competition for shells was limited because the two hermit crab species differed in size and hence occupied shells of different sizes. The total number and density of most epifaunal species were higher on shells occupied by hermit crabs than on unoccupied shells, possibly because hermit crabs prevent their shells from being buried and hence lengthen the time the epifaunal community can grow and develop. The hermit crab species also appeared to affect the epifaunal community, for the total number and density of most epifaunal species were larger on shells occupied by P. pollicaris than P. longicarpus. With increasing shell size, the populations of most epifaunal species, also were larger but not their density. Least influential in affecting the epifaunal community was the species of shells.     

Intraspecific competition and aggression for shells in the hermit crab Pagurus samuel1s

Many studies have investigated shell‐related behaviour in hermit crabs. Few studies, however, have focused specifically on the intraspecies aggression associated with shell competition. We examined intraspecies aggression in hermit crab (Pagurus samuelis) pairs as it relates to competition for a limiting resource, gastropod shells. Pairs of hermit crabs were observed in the laboratory in four different treatments that varied the presence or absence of shells for one or both of the crabs. Measurements of the latency to respond, the number of bouts, and the fight durations were recorded. There was a significant difference among treatments for all three measurements, and naked hermit crabs were much more aggressive than housed hermit crabs. There was no significant difference in aggression between males and females in any of the three treatments. The heightened aggression observed in naked P. samuelis is likely in service of acquiring a protective shell.     

Avoidance of drilled gastropod shells by the hermit crab Pagurus longicarpus at Nahant, Massachusetts

Most hermit crabs depend on empty gastropod shells for shelter; competition for appropriate shells is often severe. This study determined whether shells that have been drilled by naticid gastropods are suitable for occupancy by the hermit crab Pagurus longicarpus. Differences in the characteristics of empty shells and those occupied by hermit crabs were assessed at two adjacent field sites in Nahant, Massachusetts. Drilling damage was far more frequent in empty gastropod shells than in shells occupied by hermit crabs, suggesting that individuals of P. longicarpus avoid drilled shells. They did not appear to avoid shells with other forms of damage. Laboratory experiments confirmed that these hermit crabs preferentially chose intact shells over drilled shells, even when the intact shells offered were most suitable for crabs half the weight of those tested. Final shell choices were generally made within 1 h. The hermit crabs apparently discriminated between intact and drilled shells based on tactile cues, since crabs kept in the dark showed the same preference for intact shells. The hermit crabs strongly avoided, to nearly the same extent, artificially drilled shells, naturally drilled shells, and shells with holes artificially drilled on the opposite side of the shell from where they would normally be located. Possible selective forces causing P. longicarpus to show such strong behavioral avoidance of drilled shells include increased vulnerability of crabs in drilled shells to osmotic stress, predation, and eviction by conspecifics.     

A forced association between the slippersnail Crepidula convexa and the hermit crab Pagurus longicarpus?—possible influence from a third party

The suspension-feeding slippersnail Crepidula convexa is commonly associated with hermit crabs (Pagurus longicarpus) living in periwinkle shells (Littorina littorea) at our study site in Nahant, MA, USA. In 15 field surveys conducted at Nahant in 2000, 2001 and 2003, we found that (1) more than 61.8% of individuals of C. convexa resided on shells occupied by hermit crabs, as opposed to the shells of live periwinkles, empty periwinkle shells or other solid substrates; (2) an average of 8.3% of hermit crabs carried at least one individual of C. convexa; and (3) 39.1-75.0% of hermit crabs carrying C. convexa were carrying “large” individuals (snails with wet weight >10% of the weight of the periwinkle shells they occupied). However, it is unlikely that individuals of C. convexa seek out shells occupied by hermit crabs to colonize, and they showed no preference for empty periwinkle shells over other solid substrates in the laboratory. Moreover, in the laboratory the hermit crabs preferentially occupied intact shells bearing individuals of C. convexa only when the alternatives were shells that had been drilled by naticid snails. Thus, neither party preferentially associates with the other: rather, extensive predation by naticid snails on periwinkles at Nahant appears to limit the availability of suitable shells for the hermit crabs, forcing them to inhabit shells bearing “large” individuals of C. convexa. Individuals of C. convexa may benefit from this inadvertent association with hermit crabs: by facilitating snail dispersal, transport by hermit crabs should reduce the potential for inbreeding, an important consideration for a species that lacks free-living larvae in its life history.     

3-Decanol in the haemolymph of the hermit crab Clibanarius vittatus signals shell availability to conspecifics

Hermit crabs with poor fitting shells are chemically attracted to dying gastropods and conspecifics where a shell may become available. For land hermit crabs, the shell cue is a volatile compound found in the haemolymph. Based on this knowledge, we tested the hypothesis that shell investigation behavior in aquatic hermit crabs, the ancestral predecessors of terrestrial hermit crabs, is also triggered by volatile cues. Volatile compounds from haemolymph of Clibanarius vittatus and Pagurus pollicaris and brachyuran decapod crustaceans were purged from a water-haemolymph solution, trapped in seawater and tested for induction of shell investigation behavior with juvenile C. vittatus. Only volatiles from C. vittatus haemolymph stimulated shell investigation. Volatile compounds were isolated from haemolymph by headspace solid-phase microextraction (SPME) and analyzed by coupled gas chromatography-mass spectrometry (GC-MS). Two prominent compounds were identified, 3-decanol, which was unique to C. vittatus haemolymph, and 2-ethyl-1-hexanol, which was present in the haemolymph of all 4 crustacean species. In shell investigation bioassays, 3-decanol from C. vittatus haemolymph stimulated shell investigation behavior, while 2-ethyl-1-hexanol did not. In bioassays with synthetic 1-, 2-, 4-, and 5-decanol, shell investigation behavior was evoked by 1-decanol, 5-decanol and 3-undecanol. There was no response to 2- and 4-decanol. The response of C. vittatus to volatile shell cues supports the hypothesis that volatile cue detection evolved prior to the occupation of terrestrial niches by crustaceans.     

Land hermit crab (Coenobita clypeatus) densities and patterns of gastropod shell use on small Bahamian islands

Aim To examine patterns of abundance, density, size and shell use in land hermit crabs, Coenobita clypeatus (Herbst), occurring on three groups of small islands, and to determine how these variables change among islands. Location Small islands in the Central Exuma Cays and near Great Exuma, Bahamas. Methods Land hermit crabs were captured in baited pitfall traps and were separately attracted to baits. A mark–recapture technique was used in conjunction with some pitfall traps monitored for three consecutive days. The size of each crab and the type of adopted gastropod shell were recorded, along with physical island variables such as total island area, vegetated area, island perimeter, elevation and distance to the nearest mainland island. Results Relative abundances, densities and sizes of crabs differed significantly among the three island groups. Densities of land hermit crabs were as high as 46 m⁻² of vegetated island area. In simple and multiple linear regressions, the only variable that was a significant predictor of the abundance of hermit crabs was the perimeter to area ratio of the island. Patterns of gastropod shell use varied significantly among the island groups, and the vast majority of adopted shells originated from gastropod species that inhabit the high intertidal and supratidal shorelines of the islands. Main conclusions Although densities of land hermit crabs varied, they were relatively high on many islands, and land hermit crabs may play an important role in these insular food webs. Patterns of shell use may be strongly restricted by island geomorphology: irregular shorelines provide relatively more habitat for the gastropod species that account for the majority of adopted shells and the steep sides of the islands prevent the accumulation of marine gastropod shells. The size of adult hermit crabs appears to be limited by the relatively small gastropod shells available, while the abundance of hermit crabs may be limited by the number of shells available.     

Gastropod shells: A potentially limiting resource for hermit crabs

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.     

Shell recruitment in the Mediterranean hermit crab Clibanarius erythropus

Gastropod shells are vital for the majority of hermit crab species, being essential for their survival, growth, protection, and reproduction. Given their importance, shells are acquired and transferred between crabs through several modalities. We conducted observations and experiments at the Asinara Island (Sardinia, Italy) to investigate the efficacy of the different behavioral tactics adopted by the hermit crab Clibanarius erythropus to acquire shells, such as: (1) locomotion and activity at different tidal phases; (2) attendance at shell-supplying sites (simulated predation sites with five different odors: live and dead gastropods, live and dead crabs, predator); and (3) interactions with conspecifics in aggregations on simulated gastropod predation sites. In each tidal phase, locomotion was slow (0.7 cm min^− 1) and, as a consequence, the probability of encountering empty shells and conspecifics was low. Simulated gastropod predation sites quickly attracted a larger number of hermit crabs than the other sites tested. Aggregations seemed to function as shell exchange markets, as previously suggested for other species: the first attendant took the experimental shell and a chain of shell exchanges among conspecifics followed. Our results show that, in C. erythropus, aggregation is the most efficient tactic for the acquisition of new shells, whereas in other species, such as Pagurus longicarpus, it is associated with exploitation ability due to the intense locomotion. The interspecific plasticity in hermit crabs' behavior is confirmed.     

Ecological aspects of hermit crabs (Crustacea,Anomura, Paguroidea) off the northern coast of São Paulo State,Brazil

The occurrence of species of hermit crabs and their ecological distribution in soft bottoms off Ubatuba, São Paulo, Brazil were analyzed. To better understand the distribution of the species in relation to environmental factors, the similarity and species-diversity indexes were calculated. Paguroideans were sampled monthly from January through December 2000. The trawls were made with two otter-trawl nets at 13 different sites, at depths of 2–40 m. Water temperature, salinity, sediment texture, and organic matter content were measured. Gastropod shells occupied by hermit crabs were also assessed. A total of 1,238 specimens was collected, belonging to the families Diogenidae and Paguridae, comprising seven genera and thirteen species. The most abundant hermit crab species were Dardanus insignis (761 specimens) and Loxopagurus loxochelis (351 specimens). Phimochirus holthuisi is newly reported from the São Paulo coast. The highest diversity index was found for the shallower sites near rocky shores. The results of the grouping analysis for sites and species indicated three distinct groups for sites, and four groups for species. This suggests that the occurrence of these anomurans is associated with the environmental and biotic factors analyzed.     

Antipredator defence of the hermit crab Pagurus filholi induced by predatory crabs

Hermit crabs have two antipredator tactics: taking refuge in its shell and fleeing. We examined the following two hypotheses using the hermit crab Pagurus filholi : (1) hermit crabs change their preference for shell types that they take refuge in and/or change the timing of fleeing (i.e. the duration of refuge in the shell) when they perceive a predator threat; (2) the type of shell that a hermit crab occupies affects the fleeing tactic of the individual. Under the stimulus of a crushed conspecific, hermit crabs changed neither their preference for shell species nor their refuge duration. On the other hand, under the stimulus of the predatory crab Gaetice depressus , hermit crabs increased their preference for Batillaria cumingi shells, which provide superior protection against predators, and shortened their refuge duration in the shells even when they occupied those effective against predation. Refuge duration was longer in B. cumingi shells than in the more vulnerable shells of Homalopoma sangarense . These results suggest that both antipredator defences (changing shell and timing of fleeing) are induced by the stimulus of a predator, and the timing of fleeing is affected by the shell type occupied.     

Symbiosis of sea anemones and hermit crabs: different resource utilization patterns in the Aegean Sea

The small-scale distribution and resource utilization patterns of hermit crabs living in symbiosis with sea anemones were investigated in the Aegean Sea. Four hermit crab species, occupying shells of nine gastropod species, were found in symbiosis with the sea anemone Calliactis parasitica. Shell resource utilization patterns varied among hermit crabs, with Dardanus species utilizing a wide variety of shells. The size structure of hermit crab populations also affected shell resource utilization, with small-sized individuals inhabiting a larger variety of shells. Sea anemone utilization patterns varied both among hermit crab species and among residence shells, with larger crabs and shells hosting an increased abundance and biomass of C. parasitica. The examined biometric relationships suggested that small-sized crabs carry, proportionally to their weight, heavier shells and increased anemone biomass than larger ones. Exceptions to the above patterns are related either to local resource availability or to other environmental factors.     

Shell selection behaviour and spatial distribution of three species of intertidal hermit crabs from Hormuz Island,Persian Gulf (Crustacea: Paguroidea)

Shell selection behaviour and spatial distribution of three hermit crab species, Diogenes avarus, D. karwarensis, and Areopaguristes perspicax, were studied at six sites along the intertidal zones of Hormuz Island in the Persian Gulf. 1025 specimens were collected occupying altogether 31 shell species (D. avarus 28 species, A. perspicax 22 species, and D. karwarensis 8 species). Diogenes avarus was found to be by far the most abundant of these three crab species, and Cerithidea cingulata the dominant shell occupied by these hermit crabs. The distribution of the hermit crabs significantly varied (p<0.05) among the sites. The number and the wide diversity of shells occupied in different sites show that the main factor in shell selection for these hermit crabs is the abundance and distribution of shell species in the field.     

Examining the impact of a symbiotic lifestyle on the fecundity of the marine gastropod Crepidula plana

The marine gastropod Crepidula plana has an extensive latitudinal range along the eastern coast of the United States. It is usually found living within gastropod shells occupied by hermit crabs, although individuals can sometimes also be found living on rocks and on the exposed surfaces of shells. Our study sought to determine the extent to which residing inside periwinkle (Littorina littorea) shells occupied by the hermit crab Pagurus longicarpus at a study site in coastal Massachusetts compromises the fecundity of C. plana, through size limitation. The egg masses of symbiotic and free‐living females of C. plana included comparable numbers of egg capsules and embryos per female despite the smaller sizes of the symbionts; symbiotic females compensated for their smaller size by producing significantly more embryos per milligram of female body tissue than their free‐living counterparts. These data raise interesting questions about why—unlike its congener C. fornicata—C. plana has not yet become a successful invasive species.