Shell Selection and Behavioral Responses to Predators in Intertidal Hermit Crabs of Puget Sound

Abstract

Intertidal hermit crabs of Puget Sound include Pagurus hirsutiusculus, Pagurus granosimanus, and Pagurus beringanus. The behavior of Pagurus hirsutiusculus differs from that of the other two species in terms of shell selection, escape locomotion, and reactions to predators. Measurements of shells and hermit crab’s occupying them were taken. Both P. granosimanus and P. beringanus were found to select crabs four times their body weight while P. hirsutiusculus chose shells that were slightly lighter than it’s body weight. However, gravid females of P. hirsutiusculus choose shells twice their weight. Shell release is a unique behavior in P. hirsutiusculus in which the crab will let go of it’s shell when picked up the shell and fall out. This behavior was tested for on the other species of the intertidal, but it was found that only a large percentage of P. hirsutiusculus display this behavior. Gravid females of P. hirsutiusculus were less likely to display shell release behavior. Behavior between P. granosimanus and P. hirsutiusculus in presence of a predator was drastically different. P. hirsutiusculus recovered twice as quickly from being startled than P. granosimanus. There was no significant difference in control or predator water for either hermit crab in Cancer productus water. In Cancer magister water, there was only a significant difference in P. hirsutiusculus which went significantly slower. In P. helianthoides water, only P. granosimanus had significantly different behavior in that it recovered faster than in control water.