A Comparative Study of Aggression and Spatial Differences Between Two Populations of Pagurus bernhardus

Authors:  Dan Caven, Rachael Clayton, & Michael Sweet
Date:  September 2012



Hermit crab populations are limited by shell availability; therefore fights to gain a suitable shell are frequent. Although a large amount of research has studied hermit crab aggressive behavior, few have correlated this behavior with location. This study was carried out to investigate the influence of wave exposure on the behavior of the common hermit crab Pagarus bernhardus. Crabs from two sites on Isle of Cumbrae, with differing levels of wave exposure, were tested for their aggressive behavior in laboratory trails. Our results showed no significant difference (p > 0.05) in overall behavior between de-shelled crabs from sheltered sites and those from exposed areas. However, when the behaviors were considered independently, fighting did show significant differences (p < 0.05), possibly due to P.bernhardus from exposed sites being more aggressive. This behavior was altered when the crabs from each location retained their shells, resulting in no significant difference in overall behavior and fighting behavior (p > 0.05 and p > 0.05 respectively). This suggested that P.bernhardus is more aggressive in stressful situations (without shell protection) and this behavior is masked under normal conditions.  Predator presence (Necora purer) had no significant effect on the shell search time of de-shelled hermit crabs.