Movement patterns and dispersal of the hermit crabClibanarius longitarsusin a mangrove swamp

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Abstract
The spatial strategy of the hermit crab Clibanarius longitarsus was studied during a semilunar tidal cycle in a mangrove swamp in Kenya. This species is isospatial, being active at HW and taking refuge during its wrong phase (air) within the mangrove roots at LW. However, as revealed by radio‐telemetry, these animals (as well as other decapods) may miss one or more activity cycles. During their displacements, they followed a straight course parallel to the coast‐line but limited within a narrow and constant channel from the mangrove edge to the sea. Displacement was significantly higher at spring tides (with a maximum of 450 m), but there was no difference in extent between nocturnal and diurnal tides. Animals maintained the same locomotory sense during single HWs, and over subsequent HWs. These movement patterns were fast dispersal along the x‐axis, as revealed by both a low recovery rate of tagged animals and the trajectories followed by 12 radio‐tracked hermits. This nomadic behaviour may be explained as a means of intercepting spatially unforeseeable resources. Empty shells are a limiting factor in this habitat, and to periodically obtain new gastropod shells is fundamental for hermits (due to the animals’ growth or deterioration of old shells). Acquiring them from dead snails or conspecifics may have placed a fitness premium on this expensive spatial strategy.