Substrate Complexity Drives Hermit Crab (Diogenidae) Diversity and Ecological Flexibility Across Sand, Rubble, and Coral Habitats in Tarahan Island, Indonesia

Populations of ophiuroids were sampled from three habitats (living coral surfaces, dead coral surfaces and coral rubble) on a coral reef in Barbados, West Indies. Living coral habitats were more densely populated than dead coral or rubble habitats, while diversity indices showed that the rubble had a higher species diversity than living or dead coral habitats. The array of species and their ranked dominance was similar in the two coral habitats but both were different statistically from the rubble habitat. The mean size of individuals was greater in the rubble habitat than in the other two habitats. The degree of patchiness was uniform among the three habitats and most of the common species collected appeared to be generalists in terms of niche breadth.

Home selection and regular welcome (and not so much) guests in Iberian Hermit Crabs

During monthly intervals over a 1—year period, 12,000 empty snail shells were added to a small, isolated, rocky intertidal reef in the San Juan Islands of Washington. The shells added were species normally used by the high intertidal hermit crab, Pagurus hirsutiusculus, and were placed in locations accessible to that species. The shell additions resulted in an increase in density of P. hirsutiusculus at the experimental reef, whereas no density change occurred at a nearby control reef, indicating the importance of shells as a limiting resource. To establish the generality of shell limitation, the hermit crab populations of four unmolested rocky intertidal sites (three of which are typical hermit crab habitats) were quantitatively samples to obtain species compositions and size distributions of hermit crabs, their shells, and unoccupied shells. Shell preference experiments determined the preferred shell sizes and species for each hermit crab species. Except for small size classes, empty shells were rate at the three typical areas. In addition, hermit crab size distributions followed shell size distributions, and all but small hermit crabs of three species occupied shells smaller than the preferred size. These results support the conclusion that empty shells are a limiting resource for these hermit crabs. Since shells constitute a common, necessary resource in short supply, these hermit crabs are in competition for available shells. The fourth area, chosen for its unusual shell—availability characteristics, exhibited a different pattern of shell utilization not suggesting shell limitation. Shell occupancy at the three representative intertidal sites was examined to determine the strength of the relationship between hermit crab species composition and resource availability. Though resource partitioning was demonstrated, the presence and numbers of each hermit crab species and its preferred shell types were poorly correlated. Differences in hermit crab species composition are explained by differences in the physical habitat, and collections from other areas show that the same shell species can support different hermit crab species in different but adjacent habitat types. Thus, the mechanism allowing coexistence apparently involves both resource and habitat partitioning.

Although hermit crabs are cited as obligate users of gastropod shells, some also use portable sponge shelters. At Dog Island, Florida, in the NE corner of the Gulf of Mexico, the hermit crab Pagurus impressus occupies sponges, commonly found near shoreline in January. However, testing of P. impressus in conspecific groups and in a mixed-species assemblage (with P. longicarpus, P. pollicaris, and Paguristes hummi) confirmed that individuals of P. impressus do not prefer sponge shelters. Hermit crabs in sponges sometimes abandoned them for shells and those in shells rarely switched into sponges. Individuals of P. impressus, especially juveniles, may occupy sponge shelters due to competition from more aggressive species and/or shell-scarcity. Additional key words: sponges, Porifera, Decapoda, symbiosis, Gulf of Mexico Most pagurid hermit crabs live in empty gastropod shells, but certain species use sponges which grow on gastropod shells. The shells may be empty or occupied by either the living snail or a hermit crab. As the sponge overgrows and encloses the shell, the hermit crab uses less of the shell, occupying instead a spiralshaped chamber within the sponge and maintaining a sculpted opening to the outside (Fig. 1). These sponges, referred to in the literature as mobile sponges (van Soest 1993), are the most common sponges in some sandy or muddy bottom habitats (van Soest 1993). Portable sponge, a better name for a sponge transported by a living snail or hermit crab, will be used to refer to such sponges in this paper. This association between pagurid and portable sponge is distinct from that of hermit crabs in the genus Cancellus, which typically do not occupy shells, but instead use a variety of shelters including pieces of rock or coral, or crevices and natural chambers in other kinds of sponges (Mayo 1973). Associations between hermit crabs and portable sponges are known from the Western and Northern Pacific (Benedict 1900; Hart 1971), Chilean coast (Desqueyroux 1972), Central Atlantic (Diaz et al. in press), Eastern Atlantic (Vosmaer 1933; van Soest 1993), Scotland (Scott 1885), and Korea (Sim 1990). The best-known association involves the sponge Suberites domuncula, a Mediterranean-Eastern Atlantic species (van Soest 1993). The Florida hermit-crab sponge, as it is commonly called by local biologists (Rudloe 1984, 1991), is a compact portable sponge of uncertain taxonomy found in the NE corner of the Gulf of Mexico (Sandford 1994). It grows on gastropod shells of several species (Wells 1969; Sandford, unpubl. data), but most commonly uses the buccinid whelk Cantharus cancellarius as a substrate (Sandford 1994 and unpubl. data). Sponges are found growing on all sizes of shells (Sandford, unpubl. data), including large shells with a thin overlying sponge layer and small shells embedded in larger sponges (Fig. 1). Several hermit crab species may inhabit the sponge, but only Pagurus impressus Benedict 1892 is common in sponges found near shoreline in January, when they are relatively abundant and when most field work over the past 8 years has been done. Daily shoreline surveys for 2 weeks in July 1993 found few sponges, most in poor condition. The association between sponges and hermit crabs has been largely unstudied since first described by Wells (1969). Little has been reported on behavior of pagurids in sponge shelters, except for conjectures on possible benefits. Vosmaer (1933) assumed a mutualistic relationship between Suberites domuncula and hermit crabs, with the sponge gaining food and oxygen, and the crab benefitting from long-term protection in a living, growing shelter. Hart (1971), commenting on Pagurus stevensae from British Columbia and the sponge Suberites ficus, mentions that a hermit crab would not have to change shelters, implying that hermit crabs in living sponges might benefit from reduced e ergy costs and predation risks associated with a need to locate and contest larger shells. Such shell-switching by hermit crabs has been well documented (Wilber This content downloaded from 157.55.39.105 on Fri, 07 Oct 2016 04:29:17 UTC All use subject to http://about.jstor.org/terms

Three sympatric species of semi-terrestrial hermit crabs (Coenobita cavipes, C. rugosus and C. pseudorugosus) occur on SW Madagascar shores on the edge of a semi-desert. They have similar resource requirements, some of which are restricted, yet their populations are very abundant. All 3 species seek refuges, the type and extent of which were assessed in 5 size classes for each of the species at 6 sites. Refuge-use, principally burrowing, was governed by a series of factors: tidal range, individual size (mass), species identity, site, shade. Shell architecture did not, however, directly influ- ence refuge-use. An existing ordination technique (detrended correspondence analysis, DCA) was modified by inserting refuge identities as 'species terms' to interpret the structure underlying multi- dimensional niche space. The results show that variability in the refuge suite sought by hermit crabs serves to partition niche space both overall at the species level, and on a site-by-site basis for each species. On high spring tides, the extent of burrowing (a strategy common to all 3 species) was reduced, and a DCA of this data set showed niche compression at this tidal phase. Whilst biologically mediated niche shifts are a well-established concept, the changing of niche overlap described here clearly differs, as it is temporally dynamic and physically (tidally) driven. Inclusion of intertidal and subtidal hermit crabs at the study site into a data matrix showed that most species were separated ecologically by 4 niche dimensions: shore zone, habitat type, shell type and refugial behaviour. Niche complimentarity was clear, as species which were similar in 1 or more dimensions (such as C. rugo- sus and C. pseudorugosus) differed in other dimensions. Refuge-use of Coenobita spp. hermit crabs (and equivalent clustering behaviour of intertidal species) seems, therefore, to be multifunctional. The behaviour appears crucial to environment extremity avoidance, but may be equally important in resource management through water conservation and shell-, habitat- and shore-zone-partitioning. The results indicate that the SW Madagascar hermit crab assemblage is a speciose guild with (5D) niche complimentarity and temporally dynamic niche overlap.

symbionts incur through their association with hermit crabs. However, as Ross & Sutton (I96I) have pointed out, most of the proposed benefits have been inferred and not demonstrated. Furthermore, these particular benefits will vary depending on the species of hermit crab and symbiont. Shelter or protection from predators (Orton, 1922) and greater ease in acquir ing food are the most commonly proposed benefits. Associating with a hermit crab could help the symbionts acquire food in various ways depending on the species involved. The sea anemone, Adamsia palliata (Bohadsch), is actually fed by the hermit crab, Pagurus prideauxi Leach (cf. Fox, 1965). The polychaete, Nereis fucata (Savigny), is able to steal food from the hermit crab by placing its pharynx between the third maxillipeds of the crab (Brightwell, 1951). Other symbionts, such as the hydroid, Hydractinia echinata (Fleming) (cf. Schijfsma, 1935; Wright, 1973), and various sea anemones (Balss, 1924) share in the crab's meal by passively waiting for pieces of food to come into contact with them. While there has been some question as to how much food these symbionts actually acquire in this manner, the hermit crabs do provide mobility that presumably enhances the symbionts' chance of finding food (Balss, 1924; Ross, I960; Ross & Sutton, I96I; Jensen, 1970; Wright, 1973). Still other benefits have been suggested besides protection and food. From observations made on aquarium specimens, Wright (1973) concluded that the hermit crab's movement and respiratory current would help keep Hydractinia echinata free of sediments. Balss (1924) suggests that one benefit of the hermit crab's movement is in providing the symbionts with oxygen-rich water. Although specific benefits to particular organisms undoubtedly occur, the study reported here suggests that at least in the temperate sand littoral zone, a general benefit provided by hermit crabs is to keep the shells and associated organisms from being buried by sand. The study was conducted from October, 1972 through March, 1973 in Tampa Bay at St. Petersburg, Florida. To obtain a measure of the incidence of the burial of gastropod shells un occupied by hermit crabs, the openings of some shells were sealed to prevent entry by hermit crabs. The shells were placed in small groups at various locations within

Ecological relations between hermit crabs and their shell-supplying gastropods: Constrained consumers

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.

Annual breeding seasons of three sympatric species of tropical intertidal hermit crabs, with a discussion of factors controlling breeding

Ergaea walshi, a gastropod with a markedly flat shell, often lives inside empty snail shells occupied by hermit crabs. We investigated its lifestyle, shell growth pattern, and habitat preference for host hermit crabs and host snail shells. Four hundred sixteen snail shells, including 363 shells with hermit crabs and 53 empty shells, were collected from intertidal zones of sandy and muddy flats around Kii Peninsula, Japan. The specimens comprised seven hermit crab species occupying 24 shell species; E. walshi was harbored in 13.2% of snail shells with hermit crabs and 17.0% of those without hermit crabs. Although no preference was detected for particular species of hermit crab or snail shell, E. walshi preferred to live inside of snail shells with wider apertures used by comparatively bigger hermit crabs. This suggests that the occurrence of E. walshi was influenced by host size rather than host species. When looking at growth patterns, we found that the attached shell portion of E. walshi continued to be enlarged horizontally, while growth in shell height slowed at approximately 5.0 mm. The conspicuously flattened shell of E. walshi is considered as a growth pattern for adapting to the narrow space within the snail shell occupied by hermit crabs. Consistent with this idea, our comparison of shell growth patterns in 23 calyptraeid species showed that shell of E. walshi is the flattest in this family.

Interference and exploitation components in interespecific competition between sympatric intertidal hermit crabs

The unwanted guests of hermits: A global review of the diversity and natural history of hermit crab parasites

Symposium stream 3: The developmental morphology of parasites

Hermit crabs

Land hermit crabs are invertebrates having a unique shell and attractive behavior. In their natural habitat, they live in a group with different species. Meanwhile in an artificial habitat, they are usually maintained solitary, even solitaire that the necessities of social life are not fulfilled. This research was aimed to improve the survival rate of three species of hermit crabs (multispecies) through niche heterogeneity and to analyze their behaviors in an artificial habitat. Two treatments were evaluated including species types (multispecies combination) and habitat types (sand, hiding place, branch, open area). Coenobita perlatus preferred to climb and roam, especially at night, whereas C. brevimanus tend to burrow or hide while C. violacens preferred to hide. The highest survival rate was observed for C. brevimanus (91.66±0.143%) coexisted with two other species. C. perlatus showed the highest survival rate when they were mixed with C. brevimanus (83.61%±0.149). However, the survival was low when they were mixed with C. violacens. This result proved that hermit crabs need to coexist, but with the right species. The coexistence is possible by partitioning the resources.