Shell recruitment in the hermit crab Clibanarius erythropus.

Gastropod shells are vital for the majority of hermit crab species, being essential for their survival, growth,
protection, and reproduction. Given their importance, shells are acquired and transferred between crabs
through several modalities. We conducted observations and experiments at the Asinara Island (Sardinia,
Italy) to investigate the efficacy of the different behavioral tactics adopted by the hermit crab Clibanarius
erythropus to acquire shells, such as: (1) locomotion and activity at different tidal phases; (2) attendance at
shell-supplying sites (simulated predation sites with five different odors: live and dead gastropods, live and
dead crabs, predator); and (3) interactions with conspecifics in aggregations on simulated gastropod
predation sites. In each tidal phase, locomotion was slow (0.7 cm min−1) and, as a consequence, the
probability of encountering empty shells and conspecifics was low. Simulated gastropod predation sites
quickly attracted a larger number of hermit crabs than the other sites tested. Aggregations seemed to
function as shell exchange markets, as previously suggested for other species: the first attendant took the
experimental shell and a chain of shell exchanges among conspecifics followed. Our results show that, in
C. erythropus, aggregation is the most efficient tactic for the acquisition of new shells, whereas in other
species, such as Pagurus longicarpus, it is associated with exploitation ability due to the intense locomotion.
The interspecific plasticity in hermit crabs' behavior is confirmed.