Introducing Dr. Bulinski: Hermit Crab Researcher (Part 1)

This guest post is part one of a two part interview with Project Shellter research advisor, Dr. Katherine V. Bulinski.

Dr. Katherine V. Bulinski
Photo credit

I’ve asked Dr. Katherine V. Bulinski to serve as research advisor on Project Shellter. This interview was conducted via phone and email before and after Dr. Bulinski journeyed to Ecuador and the Galapagos Islands as part of her work as a Professor of Geoscience at Bellarmine University.

Miles Lightwood (ML): I was introduced to your work while researching Project Shellter. Would you please describe your involvement with hermit crabs?

Dr. Katherine Bulinski (KB): Sure. I’ve always been fascinated with hermit crabs and had them as pets when I was a kid, and actually still do! As part of my graduate studies I was fortunate enough to work with hermit crabs in a scientific context as a side project greatly differing from my main research area which broadly speaking, is an investigation of the paleoecology and diversity of fossil marine invertebrates.

The hermit crab project began as a part of a field course on predator prey interactions at Friday Harbor Laboratory on Puget Sound in Washington state.  I designed a study that tested hermit crab shell selection behavior when subjected to a variety of different experimental conditions including the presence of competition by other hermit crabs and the threat of an active predator.  The study revealed that the hermit crabs in the study were least likely to switch shells when exposed to other hermit crabs, which may be an indication that competition for shells is actually a greater danger to the crabs than predators.  This study was published with the title “Shell-Selection Behavior of the Hermit Crab Pagurus granosimanus in Relation to Isolation, Competition, and Predation” in the Journal of Shellfish Research (2007).  I hope some of my knowledge about hermit crab behavior can be beneficial to the project.

ML: In layperson’s terms, please describe what a hermit crab is and its place within the ecosystem.

KB: Sure. A hermit crab is a type of crustacean (the group that contains lobsters, shrimp and crabs among other organisms)  and hermit crabs have a fossil record extending back to the Cretaceous (when dinosaurs were still roaming the earth).  Hermit crabs are different from most other crustaceans in that their abdomen is not covered with an exoskeleton.  For this reason, the crab needs to cover their vulnerable soft body part with a protective covering, which in most cases is the shell left behind by a deceased snail.  As the hermit crabs grow, they need to find larger and larger shells.  When adequately sized shells are unavailable, the desperate crabs either occupy shells that are much too small for them, or may occupy whatever they can find: broken beer bottles, shotgun shells, plastic pipe. It’s sad to see.

One of the reasons why I love hermit crabs is that contrary to their name, hermit crabs are very social creatures. In the wild, they can live in groups of hundreds or even thousands (I saw a huge colony while traveling in Panama a few years ago), climbing atop one another while scavenging for food and are frequently investigating shells (whether they are empty or occupied by a snail or fellow hermit crab) as they search for a better “home”. Living in a colony ensures a wide selection of differently sized shells will be available – essential for growing crabs.

ML: We discussed some of the experiment design for the project, and you suggested several interesting strategies.

KB: Yes, well-designed experiments are critical for good science. We recently discussed the layout of the crab habitat, or the “crabitat” and established that if we wish to encourage shell switching behaviors, it should not be setup as it might be for pet hermit crabs.  While it is important to provide lots of moist sand, water and food,  there should not be any other objects in the crabitat (like sticks to crawl on).  The removal of these items would increase the likelihood that the crabs would investigate the printed shells. Once experimentation is over, the various huts and branches that make for excellent additions to a pet hermit crab terrarium can be introduced to the crabitat.

We also discussed that the various models of the printed shells should also be identified in some way. Since the plastic comes in different colors, coloration is an easy way to distinguish one shell design from another. Numbering them is another.

The interest in the use of printed shells can be assessed in a few ways:

  • Examination – Before a crab switches shells, it first investigates the new shell by rolling it around and inserting various appendages into the opening of the shell. If this behavior occurs, it validates that the crab recognizes the printed shell as a type of potential “home” whether or not the crab chooses to occupy it.  When crabs engage in these kinds of behaviors, they are ensuring that the shells are in fact empty, and the dimensions of the shell are appropriate for the crab.  Hermit crabs will often engage in this behavior, sometimes investigating the same shell multiple times before switching shells or moving on to another behavior.  It is not known whether the crabs will be deterred by a shell made out of a material other than the natural calcium carbonate that makes up natural snail shells.
  • Switching – If the shell passes examination, the crab may try on the shell, and this happens very rapidly so as to minimize the risk from predators or from other hermit crabs. Sometimes after switching shells, for whatever reason,  the crab has cold feet (or cold chelipeds in this case) and switches back to the original shell. This kind of behavior frequently occurs with natural shells so it may occur with the printed ones.
  • Adoption – When a crab adopts a printed shell and resides within it after switching to begin a new kind of behavior (e.g., eating, resting, digging in the sand)  it is likely that the hermit crab prefers the new shell over the old shell.  If this adoption happens multiple times among the different crabs residing in the experimental crabitats,  it is likely that the printed shells could be useful to the pet hermit crab trade


Part two of the interview will be available tomorrow!

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