The hermit crab is a type of crab that does not have a very hard shell. Therefore, it must find and use shells from other animals for protection. The most prevailing shelters that hermit crabs use are snail shells. This is because hermit crabs carry a portable home around with them, into when they can crawl in case of an emergency, such as biotic or abiotic stressors. Even without an emergency, the hermit crabs are constantly using their shells.  An interesting question to explore is why do hermit crabs live in snail shells? One plausible answer is that snail shells are the most available thing to the hermit crabs in the ocean. These shells are essential to hermit crabs because they minimize the loss of water from the crab’s body, which helps prevent desiccation, and also protect them from predation. There is frequently strong competition among hermit crabs for available shells. This is because as they grow, they must adopt a new shell to acquire their larger bodies.
         However, there may be certain preferences over different shell types and different environments. Past studies on hermit crabs of the genus Clibanarius show that shell selection is determined by the respective sizes of the hermit crab and of the shell species (Botelho and Costa, 2000). It is also essential for crabs to have a well-fitted shell for retreating purposes to avoid predation and desiccation. This is supported by Turra and Leite’s (2004) study, which shows that hermit crabs choose relatively thicker shells despite their heavier weight because it confers greater protection to the inhabitant. Overall, shell preference is determined by various cost-benefit balances and the life history of each species (Osorno et al., 2005).
         In our study, we were interested in the shell species selection among hermit crabs occurring in different elevations and under different rock types. Some of the questions that we wished to answer were which shells do hermit crabs prefer, which species of shells do they occur in under basalt and coquina rocks, and which intertidal zone elevation are hermit crabs most likely to live in? These questions were later answered after the comparison of data collected. We compared the species of snail shells used by hermit crabs under the coquina rocks versus basalt rocks, in two different zones; the middle intertidal and the lower intertidal zone, known in this area as “zone 3” and zone 4” respectively. The actual estimated tidal zone elevation at the time of the study was 3 feet.
         We find these questions interesting because we would like to know if hermit crabs prefer a certain snail shell over others and if the preference is conditional, meaning they prefer different shells in different environments (rock types and intertidal zone).We predicted that we would find more of a diversity of snail shell species under coquina rocks versus basalt because of the porous nature of the coquina rock and variability of food. Also, we predict that more hermit crabs would be seen in the middle intertidal zones. This prediction was made because of the stressors that are accompanies with close proximity to the wave action. Also, we expected to find more hermit crabss underneath the coquina rock versus the basalt because of the porous nature of the coquina and the availability of food source.


Authors: Jenessa Hill & Jennifer Mordaunt| Ecology 450| Marine Discovery| Created November 20,2007| University of Arizona| Class photos