ABSTRACT: The Œmolding hypothesis¹ (Elwood et al. 1979. Anim Behav 27:940-946) predicts that shell-species selection by hermit crabs may be influenced by past experience in shell use through shell-imposed alterations in crab morphology. The present studywas designed to test this hypothesis and to further the understanding of plasticity in the shell-species selection in hermit crabs. Shell use was demonstrated to influence crab growth and morphology. Individuals reared in shells of attained larger sizes than individuals in shells of . Crab growth was also dependent on crab sex, since males reached larger sizes and presented longer intermolt periods than females. The most conspicuous influence of shellutilization on crab morphology was in dorso-ventral flattening, which occurred on a decreasing scale with the shell species, as follows: > > . Crabs from all treatments and thosecollected in nature in shells of chose mainly shells of , but the previous experience of crabs strongly influenced their shell-species selection pattern. Individuals maintained in shells selectedshells more frequently than individuals reared in or . The influence of past experience was demonstrated to depend on shell type, since patterns of shell-species selection of individuals reared in or were identical. These differences in the shell-species selection pattern directly reflected the differences in crab dorso-ventral flattening, i.e. dorso-ventrally compressed individuals (those in shells of or showed a higher probability of selecting narrow-aperture shells than did Œrounded¹ individuals (those in shells of or . The weight of the selected shells at the end of the experimentdepended on crab size instead of previous experience with different shell architectures.
Zoo Med Hermit Crab "Growth" Shell, 3 Pack
Availability of habitat is an important determinant of adult population size for all animal species, and in most marine invertebrates whatever constitutes good adult habitat should also be good for the juveniles. However, if the juveniles require a habitat different from the adults, then there may exist an early bottleneck with important consequences for later population size. This idea of habitat bottlenecks at juvenile/adult size is tested with hermit crabs Pagurus samuelis and P. hirsutiusculus at 9 sites in California by increasing the abundance of juvenile "habitat" (Littorina shells) and/or adult "habitat" (Chlorostoma shells) and measuring the effect of each on adult population size. With seasonal settlement in March-April, recruits grow large enough to occupy juvenile-sized shells in 1-2mo, and large enough to occupy adult-sized shells by June-July. At each site all added shells are tethered with monofilament line to eyebolts set within tidepools. At weekly intervals the extent of occupation of tethered shells is recorded and the tethers cut to free the hermit crabs. New empty shells are added at this time. Results show that while juvenile population size is definitely limited by lack of juvenile habitat, there is no bottom-up effect on adult population size. So, addition of empty juvenile-sized shells has no significant effect on adult population size, nor does addition of empty adult-sized shells have a significant effect on adult population size, although a positive trend is evident in the data. The author suggests that adult population size in these hermit-crab species is most likely limited by recruitment.
Fluker's Hermit Headquarters Hermit Crab Growth Shells
One would expect that hermit crabs would resist or tolerate temperature and desiccation stress in accordance with the intertidal height they naturally occupy. This idea is examined by a researcher at the University of California, Irvine for 4 co-occuring in the San Luis Obispo area of mid-California, Pagurus samuelis (upper-mid intertidal), P. hirsutiusculus and P. granosimanus (mid-low intertidal), and P. hemphilli (shallow subtidal). The major experiment consists of exposing replicate groups of 20 individuals of each species in sand-filled plastic tubs in the open sun for periods of 20min. A shaded region (20% of tub area) is provided in each . Results show greatest aggregation and shade-attraction behaviour in P. samuelis, intermediate levels in P. hirsutiusculus and P. granosimanus, and lowest levels in P. hemphilli. Individuals that are over-sized with respect to size of their shells are less resistant to aerial exposure. Other similar experiments but of longer duration show that the higher-inhabiting P. samuelis survives significantly longer than the lower-inhabiting P. granosimosus. Smallest-sized individuals in these survival tests are more susceptible, as expected based upon less favourable surface area-to-volume relationships, than larger-sized ones, but for P. samuelis, at least, the superior ability of small individuals to seek out shade and protective crevices in the field allow them to live higher in the intertidal zone than expected. The overall pattern shown here suggests that the species most adept at aggregating and seeking shade, both temperature- and desiccation-resisting behaviours, and in otherwise being able to resist effects of aerial exposure, are the ones most able to exploit higher intertidal-level habitats.
Hermit Crab Growth Shells - Fluker Farms