Ecology of tropical hermit crabs at Quirimba Island, Mozambique: a novel and locally important food source

The semi-terrestrial hermit crabs Coenobita cavipes and Coenobita rugosus are both highly abundant in the supra-littoral zone of Quirimba Island, northern Mozambique. In the open sand scrub environment the principal food sources were mangrove propagules and algae for C. cavipes and rotting terrestrial vegetation for C. rugosus. Increased use of the mangrove habitats on Quirimba Island by the local human population has resulted in human faeces as a potential source of food for hermit crabs. The level of use of this resource differs between the 2 species and between habitats, but not significantly between day and night. Both species exhibited gregarious behaviour on food items, particularly C. cavipes on human faeces (up to 61 individuals on 1 food item). Both species exhibited cannibalism during the study period, but this constituted less than 1% of their diet. The foraging distances of both species increased with individual size and differed with habitat in C. cavipes.