Hermit Crab Populations Research Articles

Ecology of tropical hermit crabs at Quirimba Island, Mozambique: niche width and resource allocation

Intertidal-zone hermit crab populations in the Quirimba Archipelago occur in high den- sities and many species overlap considerably in terms of spatial distribution and types of shell used. The suites of shells used by 5 mid- to supra-littoral hermit crab species were studied (using multi- variate analyses) across 3 shore zones, 7 islands and several levels of mollusc fishing pressure. Poten- tially high intra- and inter-specific competition for resources in the Quirimba Archipelago hermit crab assemblages is alleviated by a degree of macrohabitat and shore zone separation but largely by sig- nificant partitioning of shell resources. The suite of shells used by each species was distinct, even if certain types were in common. The highest influence on shell usage was tidal height followed by shore-zone area and hermit crab identity. Where the spatial distributions are tighter (in the supra- littoral), the resource (shell) partitioning is greater. Fishing pressure (and associated abundance of target-species shells) was generally unimportant, but 1 species, Coenobita cavipes, used harvested shells opportunistically in proportion to their availability. Shannon H ' and species-richness values of shells used increased with shore zone area in the upper shore zone but not in the supra-littoral zone. It is suggested that this was due to high fishing pressure on certain mollusc species making certain shells abundant for hermit crabs (shell middens were deposited on the supra-littoral zone). The results suggest a tight niche mosaic of the many hermit crab species in the Quirimba Archipelago.

The Distribution of Hydroid Sibling Species on Hermit Crabs in Estuaries in the Gulf of Maine

Estuaries in the Gulf of Maine contain disjunct, isolated populations of a number of invertebrate taxa typically distributed only sound of Cape Cod. These estuarine populations may either be remnants of a southern fauna that were stranded by Quaternary changes in water temperature, or they may have been established more recently via larvae that entered the estuaries from the open ocean. We tested these hypotheses by examining the distribution of sibling species of hydroids that are symbiotic on paguriid hermit crabs. These crab-hydroid species pairs differ greatly in their ability to colonize new areas through the water column. The hermit crabs possess a planktonic larva that can disperse great distances, while the hydroids have a crawling planula larva that is extremely limited in its dispersal capabilities. Consequently, estuarine hermit crab populations that lack their native hydroid symbiont are likely to have originated by larval colonization. Hydroid sibling species were identified on the basis of MDH electromorphs. Species identifications were confirmed through a limited number of test matings with colonies of known species identity. In three out of the four estuaries that we examined, shells inhabited by the southern hermit crab,Pagurus longicarpus, were occupied only by the local northern hydroid,Hydractinia polyclina. This pattern is consistent with a more recent establishment of the hermit crab populations through larval dispersal or transport. However, in Casco Bay, shells inhabited byP. longicarpus were occupied by a mixture of the northern hydroid,H. polyclina, and the southern hydroid,H. symbiolongicarpus, that is associated withP. longicarpus throughout the southern part of its range. Thus, theP. longicarpus population in Casco Bay may either be a relict of a former, more broadly distributed population of this crab in the Gulf of Maine, or if recently established, is likely to have originated by the introduction of adult crabs with hydroid-covered shells.

Gastropod predation sites: the role of predator and prey in chemical attraction of the hermit crabClibanarius vittatus

Gastropod shells are essential to most hermit crabs. Shell availability limits hermit crab populations. Shells provide protection and the degree of shell-fit controls crab growth and fecundity. Crabs locate new gastropod shells from a distance under water by molecules released from gastropod flesh during predation events. Here we test the hypothesis that the salivary glands of the predatory gastropod are the source of enzymes that digest muscle proteins and release peptide attractants. We describe the anatomy of both the acinous salivary glands and the tubular accessory salivary glands ofBusycon contrariumwhich are similar to those ofB. carica. The salivary gland ducts empty at the mouth, suggesting a role in the primary digestion of food. We show that gastropod muscle proteins, extracted by salt solutions with the ionic strength of sea water and purified by precipitation in low ionic strength can be digested by gastropod salivary gland enzymes to generate peptides attractive to the hermit crab,Clibanarius vittatus, in field assays.

Bathymetric distribution of hermit crabs (Crustacea: Decapoda: Anomura) from the Otago New Zealand

Abstract An account of the distribution and abundance of 16 species of hermit crabs in the Otago region is given, based on semi-quantitative trawl samples from subtidal stations off the Otago Peninsula and adjacent coast, and on intertidal samples. Intertidally, hermit crab population density is very low (0–0.08 crabs m-2). Subtidally, population density is highest between 20 and 120 m (1. 6–13.1 crabs m-2). Be~ond the shelfbreak (at c. 200 m), population density is again low (0.1–2.5 crabs m-2). Three major species assemblages are present: an intertidal assemblage with two species, a continental shelf assemblage with ten species, and a slope (canyon) assemblage with seven species. For the majority of shelf species, a Nearshore zone (0–20 m) and an Outer Shelf zone (120–200 m) represent respectively their upper and lower distributional limits and few hermit crabs live in these transitional zones. Some shelf species appear to have more limited distributions: Pagurus n.sp.A between depths of 4–12 m on well sorted sand in association with large populations of the gastropod Umbonium zelandicum; Paguristes pilosus between depths of 14–40 m on high energy coarse sand bottoms; Pagurus n.sp. B in water shallower than 120 m; and Pylopagurus stewarti at depths greater than 40 m. Some shelf species spill over beyond the shelf break, but only one species (Pylopagurus stewarti) attains large population densitites on both shelf and slope. Four species are found exclusively in the canyon zones.

Positive abundance and negative distribution effects of a gastropod on an intertidal hermit crab.

Field experiments were used to determine the effect of a common intertidal snail (Nerita funiculata) on the use of space for foraging by the hermit crab Clibanarius digueti. Removals of Nerita resulted in an increased density of foraging Clibanarius, while additions of the gastropod had the opposite effect. The observed negative effect of the gastropod on individual hermit crabs appears to be food-related. Field surveys, however, suggested that the hermit crab population is limited by shell number, rather than food. Because Nerita contributes to the shell resource, its effect on the hermit crab population is positive. Nerita, therefore, has a negative effect on the distribution of foraging hermit crabs, but a positive effect on their abundance. Such decouplings of distribution and abundance effects are rare.

Effects of Sampling Method on the Estimation of Population Parameters in Hermit Crabs

Hermit crabs were collected from intertidal and shallow nearshore habitats in the vicinity of Alligator Harbor, Florida, either by visual search of prescribed areas along transects or by collection of crabs that were attracted to baits of gastropod flesh (mimicking natural predation sites). The two sampling methods produced collections that were closely similar in crab species composition and relative abundance and in the relative abundance of the shells of the common gastropod genera that the crabs inhabited. The two collections differed in the following respects: (1) more individuals were collected at baits, (2) crabs attracted to baits probably were more secretive and less mobile, (3) significantly more crabs collected at baits occupied damaged shells (72.2%) than did those located by visual search (29.9%), (4) crabs attracted to baits occupied shells of more gastropod genera (22) than did those collected on transects (14), and (5) more individuals of small size and crabs of a wider size range were collected at baits. Our data suggest that the two methods sample different types of individuals with different efficiencies. Small secretive crabs that occupy damaged shells arc underrepresented in collections made by visual search, while larger crabs in intact shells are underrepresented at baits. Estimates of hermit crab population parameters probably should be based on a combination of sampling methods.

Predaceous gastropods regulate new-shell supply to salt marsh hermit crabs

Marsh hermit crabsPagurus longicarpus Say directly acquire new shells as the predatory gastropodMelongena corona Gmelin consumes marsh periwinkles,Littorina irrorata Say. The influx rate of new shells into a salt marsh hermit crab population was measured by marking live periwinkles and daily recovering the shells from hermit crabs over periods of 3 to 6 d. Average rates of new shell acquisition ranged from 4.0 to 23.3 new shells per day from salt marsh areas of 4×10 m. Such consistently high rates contrast with the negligible rates generally assumed for new shell entry into hermit crab populations. The number of new shells acquired each day varied directly with the number of the predatory gastropod,M. corona, present in each study area at both natural and manipulated predator densities. Empty shells on the substrate are usually considered as the primary source of new shells to hermit crabs. However, over 500 empty shells had to be placed on the substrate in a 4×10 m area to provide a daily rate of 20 new shells to the hermit crab population.

New shell acquisition in the hermit crab,Pagurus geminus

The process of how the hermit crab,Pagurus geminus, acquires a new shell was investigated in the natural habitat at Ezura in Shirahama, Wakayama Prefecture, during the non-breeding season, and the following results were obtained. Hermit crabs acquired new shells most frequently by shell exchange between 2 individuals and occasionally by attacking snails. Acquisition through location of empty shells was not found. At the snail attacking site or the site of shell exchange attempts, sometimes many other individuals appeared and, frequently, confusing or complex shell changes were observed. The importance of introduction of fresh shells to a hermit crab population and the possibility for a certain individual to acquire a shell introduced by others through shell exchange attempts are discussed.

Environmental resistance and the ecology of coexisting hermit crabs: Thermal tolerance

Tolerance to increased water temperatures was determined for four, coexisting species of intertidal hermit crabs, Pagurus samuelis (Stimpson), P. hirsutiusculus venturensis (Coffin), P. granosimanus (Stimpson), and P. hemphilli (Benedict), of central California. All species showed significantly different median survival temperatures after acclimation to both 12 and 20°C. The tolerances corresponded with the intertidal zonation of the species. There was a significant increase in tolerance with an increased acclimation temperature in all species. Size had no effect on the tolerance of P. samuelis. The results support the hypothesis that differential genetic capacities of tolerance are important in influencing distributions. These findings and behavioral observations indicate that thermal conditions comparable with those created by the effluent of electricity generating facilities can cause considerable mortality to hermit crab populations on a local level.

Hermit crab fitness: The effect of shell condition and behavioral adaptations on environmental resistance

The degree of three behavioral responses (aggregation with other individuals, movement towards shaded locations and shell exiting) shown by the coexisting hermit crabs, Pagurus samuelis (Stimpson), P. hirsutiusculus venturensis (Coffin), P. granosimanus (Stimpson) and P. hemphilli (Benedict), when aerially exposed, corresponded with their pattern of intertidal vertical zonation. The highest occurring species, P. samuelis, exhibited significantly greater tendencies to aggregate with other individuals and to seek refuge in shaded locations and usually remained within their shells when exposed to the combined stresses of temperature and desiccation. P. hirsutiusculus and P. granosimanus, primarily mid- to low-intertidal species, displayed these responses only occasionally while P. hemphilli, a lowintertidal and shallow-subtidal species, showed significantly lower clustering, shade attraction, and shell abandonment responses. Comparison of larger and smaller P. samuelis revealed no significant behavioral differences. P. samuelis and P. granosimanus that occupied shells not allowing complete retraction were less resistant to the stresses of aerial exposure. Crabs inhabiting damaged shells with holes ( ≈ 5 mm diam.) in the whorls or spire did not experience decreased survival in comparison with that found in crabs occupying entire shells. These findings suggest an implication of shell optimality with environmental resistance that should be considered of potential importance in the evolution of complex communicative and aggressive behavior in intertidal hermit crabs. In addition, attraction to shaded areas and clustering are behavioral responses appropriate for avoiding or reducing the adverse effects of temperature and desiccation stresses. These responses may be important in facilitating the coexistence of these species although further investigation is needed to quantify the importance of such behavior to intertidal hermit crab populations. The significance of shell-exiting is not specifically known but survival of a shell-less crab is undoubtedly minimal.

Shell preference and utilization patterns in littoral hermit crabs of the bay of Panama

Shell utilization patterns of three sympatric hermit crab species from the Bay of Panama are examined. Shell preferences, as shown by laboratory choice experiments and the selective use of empty shells experimentally added to hermit crab populations, are shown to be important determinants of shell utilization under natural conditions. Factors which influence the types and sizes of shells occupied by hermit crabs in separate populations include: (1) the presence and relative abundance of different gastropod species; (2) the specific shell preferences of different hermit crab species; and (3) the presence and relative abundance of sympatric hermit crab competitors for the limited supply of empty shells. Since the size and type of shell occupied by a hermit crab influences its growth rate and reproductive output, these factors appear to have a direct effect on hermit crab fitness and the demographic structure of separate hermit crab populations.

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.

Movement, activity pattern, and rôle of a hermit crab population in a sublittoral epifaunal community

The movements and activity of hermit crabs in a sublittoral soft-bottom community in the North Adriatic Sea (Gulf of Trieste) were monitored by means of observations by a SCUBA diver and time-lapse photography. Tagging experiments showed that the hermit crabs exhibit a pattern of movement which causes them to remain in a defined area for extended periods. During a two-year period, the radius of activity of a crab is estimated to be under 15 m. This leads to a high recovery rate of tagged shells. The average speed of a hermit crab was 2.1 m/h and the average distance travelled per day was 21.6 m as calculated from the analysis of the time-lapse films. This distance is an order of magnitude larger than that estimated from the tagging experiments (1.1 m/day). The activity of the crabs was restricted to the sediment surface between multi-species clumps. The approximate area of the sediment surface traversed by a crab is 0.4 m 2/day. Many inter- and intraspecific encounters were observed, particularly among hermit crabs and the brittle stars Ophiothrix quinquemaculata (D.Ch.) and Ophiura lacertosa (Pennant). The daily activity pattern of the crabs is related to the light and dark phases on the sediment surface. The high density and conspicuous activity of the hermit crabs point to the important rôle of the pagurids in the investigated community.

AVAILABILITY AND USE OF SHELLS BY INTERTIDAL HERMIT CRABS

During a six-year period, several thousand intertidal snails, Thais lamellosa and T. emarginata, were given individually numbered tags and times of death were noted. These snails provided most of the shells used by intertidal hermit crabs (primarily Pagurus granosimanus). Therefore changes in the hermit crab population can be related to shell availability. The crab population increased greatly during 1969, and then declined steadily until the end of the study (1973). Changes in the crab population were highly correlated with shell availability. This hermit crab population will remain constant in size if 0.8 shells become available for each crab each month.

Competition and Mechanism of Coexistence in Three Sympatric of Intertidal 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.