Relative Growth and Sexual Maturity of the Hermit Crab Paguristes erythrops (Anomura, Diogenidae) from South Atlantic

Some morphometric relationships were studied in the hermit crab Paguristes erythrops to describe its relative growth and the size at which sexual maturity is reached, as well as the shell influence on this process. Individuals were collected monthly from January to December/1999, by SCUBA diving and 12 different characters were measured on males and females. Sexual size dimorphism was observed in length and width of left cheliped. Size at sexual maturity was estimated between 2.8 and 3.5 mm shield length based on the left cheliped relations of the males and on the endopod and exopod of the second pleopod of the females. Differences in the allometry of individuals occupying different shell species were observed. The present work demonstrated the importance of characterizing the type of growth of some parts (pleopods) not yet used in other studies on relative growth of hermit crabs that may correspond to indicators of the size at sexual maturity.     

Plastic proteans: reduced predictability in the face of predation risk in hermit crabs

Variation in behaviour occurs at multiple levels, including between individuals (personality) and between situations (plasticity). Behaviour also varies within individuals, and intra-individual variation (IIV) in behaviour describes within-individual residual variance in behaviour that remains after the effects of obvious external and internal influences on behaviour have been accounted for. IIV thus describes how predictable an individual''s behaviour is. Differences in predictability, between individuals and between situations, might be biologically significant. For example, behaving unpredictably under predation threat might reduce the chance of capture. Here, we investigated the duration of startle responses in hermit crabs, in the presence and absence of a predator cue. Individuals differed in startle response duration (personality) and while individuals also varied in their sensitivity to risk, mean response time was greater in the presence of a predator (plasticity). Moreover, IIV was greater in the presence of a predator, providing some of the first evidence that the facultative injection of unpredictability into behaviour might represent a strategy for dealing with risk.     

Hermit crabs as bioindicators of recent tributyltin (TBT) contamination

Evaluation of the assimilation pathway and depuration time of a given pollutant by aquatic species is important to understand the dynamics of this substance in the biota, and to search for potential ecological indicators. In the present study, the uptake pathway and depuration time and rate of the pollutant tributyltin (TBT) were investigated in the omnivorous hermit crab (Clibanarius vittatus). The assimilation and uptake pathway were investigated using hermit crabs collected in an area free of TBT. The crabs were held in the laboratory for 45 days, under one of four treatments: procedural control (PC) - water and food without TBT; T1 - water with and food without TBT; T2 - water without and food with TBT; and T3 - water and food with TBT. To determine the depuration time, the crabs were collected in a contaminated area, maintained in the laboratory with clean water, and removed every 15 days for 120 days. The concentrations of TBT and DBT (dibutyltin) were determined by chromatographic analysis. The TBT was taken up by the crabs mainly via food, and the presence of DBT in crab tissues was hypothesized to result from internal TBT degradation. TBT (as well as DBT) was depurated rapidly by C. vittatus. After approximately 30 days, the initial concentration of 111 ± 36 ng Sn g⁻¹ w. w. decreased to 3 ± 3 ng Sn g⁻¹ w. w., and after 75 days the TBT concentration was below the detection limit. The same pattern was recorded for DBT, which showed a higher depuration rate than TBT. The rapid TBT and DBT depuration is useful information, since C. vittatus and possibly other hermit crabs may be used as indicators of recent or recycled environmental contamination.     

Resource assessment in hermit crabs: the worth of their own shell

Animals gather information about the quality of a resource throughits assessment and behave accordingly as a result of adaptivemotivational changes. In the hermit crab Pagurus longicarpus,we investigated whether an individual was affected in its motivationto acquire a new shell by the quality of the domicile shell(own resource value [ORV]), of the offered shell (external resourcevalue [ERV]), or of both and asked whether its motivation wasaltered by the information gathered during shell investigation.We analyzed the behavior of hermit crabs inhabiting shells ofdiffering qualities and compared their willingness to acquirean offered shell—optimal, smaller than optimal, or largerthan optimal—by measuring the latency to approach it,the number of shell investigation, and its total duration. Crabsin smaller shells (SSs) approached more quick and often theoffered shell, whereas crabs in larger shells investigated theoffered shell more thoroughly. The readiness of crabs to approachthe offered shell and the extent of its investigation were independentof the ERV but were exclusively affected by the ORV, whereasthe number and duration of shell investigation did not changewith time as investigation proceeded, except for crabs in SSs.These results suggest that P. longicarpus' motivation to acquirea new shell is exclusively influenced by the value of the shellit inhabits rather than by the quality of the shell it is offeredand that this species does not gather—or does not use—informationabout ERV during investigation.     

Reproduction Strategy of the Deep-sea Hermit Crabs Pagurus alatus and Pagurus excavatus of the Central-Western Mediterranean Sea

Some aspects of the reproductive biology of two hermit crabs Pagurus alatus (Fabricius, 1775) and P. excavatus (Herbst, 1791) were studied. Specimens were collected monthly from April 2000 to March 2001 on the continental shelf and the upper-middle slope off the Southwestern coasts of Sardinia, in the central-western Mediterranean Sea. Crab size (minimum and maximum shield length) was 1.7 and 9.5 mm for 1150 females of P. alatus; 4.0 and 10.4 mm for 347 females of P. excavatus, respectively. Females of P. alatus with ripe ovaries were only found in February-April and ovigerous females were observed throughout the year except in March, with the highest incidence in summer. Females of P. excavatus with fully developed ovaries were collected during all months of the year reaching a peak from April to June. Ovigerous females of P. excavatus occurred throughout the year and the main spawning period occurred in March and April. Fecundity of both species was calculated to assess seasonal variation of reproductive intensity and was positively correlated with the size of the individuals. Monthly fecundity did not reveal significant differences in P. alatus ovigerous females, whereas P. excavatus exhibited significant differences in monthly fecundity depending on the time of year. Difference in fecundity among P. alatus and P. excavatus can be related to the size of the ovigerous females and species of hermit crab, but their different reproductive strategies suggest that they are specifically related to different environmental conditions.     

The effects of history on the shell preference of the hermit crab Pagurus longicarpus (Say)

The effect of disturbance by two macroinvertebrates, the sand dollar Mellita quinquiesperforata (Leske) and the sea pansy Renilla reniformis (Cuvier) on meiofauna was studied on a sandbar in North Inlet, Georgetown, South Carolina. Abundances of nematodes and the harpacticoid copepod Apodopsyllusunguiformis Coull &; Hogue decreased significantly in the presence of sand dollars; other taxa were not affected. In two Renilla experiments, one natural and another where artificial and real Renilla were implanted, we could determine no consistent effect on any meiobenthic taxon. However, sediments disturbed by implanting living and artificial Renilla returned to ambient levels within 1 h.     

Bitter crab syndrome in two species of king crabs from the Sea of Okhotsk

The disease caused by parasitic dinoflagellates of the genus Hematodinium was found in the red Paralithodes camtschaticus and blue P. platypus king crabs from the Sea of Okhotsk. The hemolymph of diseased crabs was cream colored, opaque, and dense. Numerous dinokaryotic trophonts and multinucleate plasmodia of the parasite were revealed in the hemolymph and internals of diseased animals. The parasitic infection was recorded in females and juvenile males from August to mid-October.     

Comparing the strength of behavioural plasticity and consistency across situations: animal personalities in the hermit crab Pagurus bernhardus

Many phenotypic traits show plasticity but behaviour is often considered the 'most plastic' aspect of phenotype as it is likely to show the quickest response to temporal changes in conditions or 'situation'. However, it has also been noted that constraints on sensory acuity, cognitive structure and physiological capacities place limits on behavioural plasticity. Such limits to plasticity may generate consistent differences in behaviour between individuals from the same population. It has recently been suggested that these consistent differences in individual behaviour may be adaptive and the term 'animal personalities' has been used to describe them. In many cases, however, a degree of both behavioural plasticity and relative consistency is probable. To understand the possible functions of animal personalities, it is necessary to determine the relative strength of each tendency and this may be achieved by comparison of statistical effect sizes for tests of difference and concordance. Here, we describe a new statistical framework for making such comparisons and investigate cross-situational plasticity and consistency in the duration of startle responses in the European hermit crab Pagurus bernhardus, in the field and the laboratory. The effect sizes of tests for behavioural consistency were greater than for tests of behavioural plasticity, indicating for the first time the presence of animal personalities in a crustacean model.     

Trophic relationships of juvenile blue crabs (Callinectes sapidus) in estuarine habitats

Salt marshes and shallow-water macroalgal beds are known to provide nursery habitat for many species of fish and invertebrates. The role of these habitats as refuge from predation is well established, but the degree to which indigenous primary production within the nursery provides food for growth and development of estuarine species remains unresolved. In this study, we tested the hypothesis that juvenile blue crabs depend on indigenous primary production, directly or indirectly, during their entire stay within the nursery. To test this hypothesis, we conducted isotopic studies and stomach content analyses of juveniles from habitats near the mouth of Delaware Bay and from an adjacent lagoonal estuary (ca. 39.5° N, 75.1° W). Primary producers, marsh detritus, various life-history stages of blue crabs and potential prey species were sampled in the main estuary and in an adjacent marsh during the summer and early fall of two consecutive years. Newly settled juveniles (<15 mm carapace width) from the marsh were about 1.8‰ lighter in carbon (−17.2‰) relative to larger juveniles from the marsh (15–30 mm carapace width) and appeared to have retained a carbon isotopic signature indicative of the phytoplankton-based food web associated with larval stages. However, the signature of juveniles changed as a function of size. Large juveniles and crabs >60 mm were enriched in δ¹³C (−14.7 ± 0.1‰) compared to small crabs, suggesting a gradual shift in diet from a planktonic to a detritus-based food web with increasing size. As with crabs from Delaware Bay, the δ¹³C signature of juvenile crabs sampled from macroalgal beds in the lagoonal estuary (Rehoboth Bay) changed as a function of size. Also, δ¹³C ratios of crabs varied among the various species of macroalgae. The δ¹⁵N composition of primary producers in the marsh and main estuary also was reflected in the δ¹⁵N values of crabs and other benthic consumers in the respective habitats. Results of stomach-content analysis in this study were consistent with isotope data. Observed changes in prey preferences were related to changes in size of juvenile crabs and also differed among habitats. Gut content analyses of the three size classes of juveniles in macroalgal beds from Rehoboth Bay indicated that the crabs depend heavily on various amphipod species that occur on the seaweeds. These amphipods graze directly on the macroalgae and are among the most abundant invertebrates in the macroalgal beds. This implies a direct trophic relationship between the juvenile crabs and the macroalgae. In summary, our study provides strong evidence that the value of nursery areas such as salt marshes and macroalgal beds goes beyond that of providing refuge from predation, and that species using these nurseries (e.g. juvenile blue crabs) are ultimately dependent on primary production originating in benthic plants indigenous to the nursery.     

Chemical recognition by hermit crabs of their symbiotic sea anemones and a predatory octopus

The ability of the hermit crabs Dardanus venosus and Pagurus pollicaris to recognize chemically their symbiotic sea anemone Calliactis tricolor and a common octopus predator, Octopus joubini, were studied. The crabs were tested for chemoreceptive responses using a Y-trough olfactometer, which prevented visual cues from being used. Choice tests showed that D. venosus could chemically detect Calliactis. If, however, D. venosus had a Calliactis on its shell at the time of the trial, it could not detect the test anemone. P. pollicaris (without a symbiotic anemone) did not locate the test anemone. Both species of crab avoided a water current carrying octopus chemical cues. Chemoreception may play an important role in the interaction of a hermit crab with its symbiotic anemone and an octopus predator.     

Response of fiddler crabs (Uca tangeri) to video playback in the field

The fiddler crab Uca tangeri communicates using a visual waving display and a vibratory drumming signal, both thought to function in mate attraction. Using video playback techniques, images of an empty mudflat, a waving male, a threatening male, and a wandering female were presented to male subjects. All stimuli elicited similar levels of low-intensity waving, but significantly more high-intensity waves were elicited by the female and threatening male stimuli than the mudflat stimulus or the waving male stimulus. This concurs with other research that the waving display is used at a higher intensity to attract females. The threatening male stimulus failed to elicit the same response as an actual threatening male and we discuss the likely reasons for this. The subjects also spent a significantly greater proportion of time drumming during the male waving stimulus than during the female stimulus, suggesting that drumming functions in male-male competition as well as female attraction. Received: 18 October 1999 / Received in revised form: 25 November 1999 / Accepted: 10 December 1999     

Frequency of moulting by shore crabs Carcinus maenas (L.) changes their colour and their success in mating and physiological performance

Male shore crabs, Carcinus maenas [Linnaeus, 1758], compete aggressively for access to receptive females to mate. Size is the single most important factor for the outcome of these conflicts, large males with carapace width (CW) over 60 mm being much more likely to gain access to receptive females than smaller males. To compete aggressively, large male shore crabs decrease moulting frequencies and may potentially terminate moulting to enter a state of anecdysis, in which further growth is suspended to increase reproductive output. This change from a “growth” strategy to a “reproduction” strategy results in the creation of two morphs, which can roughly be separated by their colouration. As the new exoskeleton created during moult is always green in appearance, crabs tend to be green in appearance during periods where they grow rapidly and moult frequently. Green crabs are found in all size classes. However, as the exoskeleton becomes older, the colour gradually changes to a darker red colour, and large crabs that have spent an extended period in intermoult are therefore often red in appearance. Also, the exoskeleton of red crabs exhibits a higher incidence of epibionts and wear and tear. Red crabs can also be found in all size classes, but their relative proportion in the population increases dramatically in size classes above 60-mm CW. Size for size, the red morph has a thicker carapace and larger master chelae than the green morph. Also, the reproductive indices (RI) for red crabs are higher than for green crabs, and they experience higher mating success. However, this mating success appears to be achieved at the expense of a lower physiological tolerance, green crabs being better adapted to deal with changes in the surrounding environment. This increased tolerance is not only observed with regard to natural variations in the habitats where shore crabs live, but green crabs also appear to be more tolerant to variations caused by anthropogenic pollution. Consequently, the shift from growth to reproduction exerts a profound effect on the behaviour, physiology and ecotoxicology of male shore crabs. The present paper reviews the studies conducted so far, proposes a mechanism by which some of these differences between the two morphs are created and discusses their ecological and ecotoxicological significance.     

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.