Hermit crabs inhabit gastropod (snail) shells for protection and engage in a constant process of shell switching throughout their lives. This process of shell switching occasionally leads to a vacancy chain, in which the discarded shell of one crab is inhabited by another crab, and the limited but reusable resource of gastropod shells trickles down throughout a population. Unfortunately, in many populations, high-quality shells are scarce, and hermit crabs can be found inhabiting litter and other detritus (such as pens or shells with holes). This switching process has potential implications for how hermit crabs reproduce, molt and grow throughout their lives. For hermit crabs, gastropod shells represent a resource as important as entire territories and habitats for other organisms, making it an important topic of study in terms of marine ecology.

Project Objectives

  • Determine the aggregate benefits of vacancy chains, created by shell-switching, in terrestrial hermit crabs
  • Determine the effect of previous shell quality (damaged or crowded) on future success in shell acquisition
  • Assess the degree to which observed patterns in shell-switching in terrestrial hermit crabs are also present in populations of marine hermit crabs

A hermit crab

(Photo by R. Rotjan)

Keeping their eyes on the prize,

hermit crabs prepare to move out

and move in once the largest crab

in the foreground secures its new,

currently vacant, home.

(Photo by R. Rotjan)

Terrestrial Crab Shell Collection

Vacancy chains represent a potential source of fitness improvement for many species that share resources that are limited to use by a single individual at a time, discrete and reusable. In both the field and the lab, we run experiments to determine the aggregate benefits of shell switching. Using a number of different crab densities in controlled lab settings (e.g. one-on-one competition for a novel shell versus a collection of crabs at various levels of size-dependent dominance introduced to a novel shell), we have attempted to assess the social context of shell switching behavior, in collaboration with Dr. Sara Lewis at Tufts University. Hermit crabs are model organisms for studying vacancy chains, and this research can be applied to any species that uses a discrete and limited resource.

Marine Crab Shell Selection

Just as we have demonstrated aggregate benefits of vacancy chains in terrestrial crabs, we are similarly investigating these questions in marine hermit crabs. Our previous studies have also determined that terrestrial crabs with damaged shells are more likely to switch shells than crabs with crowded shells, and we hope to discover whether the same switching pattern holds true for marine populations. This project will utilize agent-based models in collaboration with Dr. Jeff Chabot (Pfizer), and will enable us to compare the shell switching behaviors of terrestrial versus marine hermit crabs.