Sex- and size-related differences in shell use by the intertidal hermit crab Clibanarius erythropus (Latreille, 1818) (Decapoda: Diogenidae) in the Gulf of Cádiz, southwestern Spain

Abstract

Clibanarius erythropus (Latreille, 1818) is the dominant hermit crab in intertidal rocky habitats of the Gulf of Cadiz (southwestern Spain). Three different populations of this species were sampled during the reproductive (July 2014) and non-reproductive (October 2014) periods to assess shell use patterns in the field by different demographic groups in absence of interspecific competition for shell-resource use. Irrespective of sampling sites and periods considered, sex ratios were female-biased (2.3 on average), and mean sizes of males were greater than those for females. At least shells from 31 different gastropods were used by C. erythropus in the Gulf of Cadiz. Shell selection was largely determined by the sizes of the hermit crab and shells. As result, a generalist pattern of shell use was displayed by this species. Most hermit crabs with shield length > 4.5 mm were males and the less abundant larger shells were occupied by these large males. Statistically significant sex-related (males vs. females) and size-related (small males vs. large males) differences in shell use were observed at two sampling sites with higher shell diversity, suggesting partial intraspecific partitioning of shell resource. There was a negative effect of carrying relatively heavy/large shells on the stage condition (males and females) and on clutch size of ovigerous females, suggesting that protection from predators was prioritised.