Hefting Heavy Shells: Sustenance Demands Caused by Various Abodes of the Hermit Crab Pagurus granosimanus

Abstract

Marine hermit crabs inhabiting different species of shells in the rocky intertidal may receive varied benefits and costs. Thick shell walls, sculpture, and certain silhouettes may increase protection against crushing predators and waves, but also the energy cost for bearing such a shell. To determine the relative energy demands on Pagurus granosimanus supporting one of three different species of shells commonly inhabited in nature, we measured the consumption of food by free-roaming, size-matched individuals after four days of food deprivation in the laboratory. Surprisingly, while all hermit crabs consumed a significant amount of food, that amount did not differ significantly across the types of shells inhabited, despite the significantly heavier weight of one type of shell (>150% of each of the other two species), and markedly different shell silhouettes. Whether our results were due to the inherent abilities of arthropods to support proportionally immense weights (physiology), reduced movements by animals in heavier shells (plastic behavior), or the way the hermit crabs bear the burden of the shell requires further investigation. Regardless, our results suggest that individuals of P. granosimanus that inhabit heavier shells that likely provide increased protection do not experience corresponding elevated food consumption requirements over the short term, even if those shells are not centered over the body mass of the hermit crab. Pagurus granosimanus crabs can bear the burden.