Phylogeography of the Christmas Island blue crab, Discoplax celeste (Decapoda: Gecarcinidae) on Christmas Island, Indian Ocean

The land crab, Discoplax celeste (Gecarcinidae) is endemic to Christmas Island in the Indian Ocean. Due to a freshwater-dependant life history, in which the megalopae migrate from the ocean up freshwater streams to their adult terrestrial/freshwater habitat, D. celeste inhabits only a few isolated locations on the island. This restricted distribution is one of a number of factors which has previously highlighted the vulnerability of this species to outside threats. A number of anthropogenic factors including the introduction of multiple invasive species and habitat destruction have led to drastic ecosystem change on Christmas Island. The aim of this study was to investigate whether the restricted geographical distributions of D. celeste populations contribute to significant genetic structuring across Christmas Island, with an objective to inform future conservation strategies for this species on Christmas Island. Fragments of the mitochondrial cytochrome oxidase I gene and the control region were sequenced from 95 individuals collected from all five locations on Christmas Island known to be inhabited by D. celeste. Analyses using analysis of molecular variance revealed no evidence of population sub-structuring, indicating that despite any geographical isolation, there is a single population of D. celeste on Christmas Island. This lack of population differentiation is probably explained by the oceanic dispersal of larvae, rather than terrestrial migration of D. celeste. Therefore, based on these results, for conservation purposes, D. celeste on Christmas Island can be considered a single management unit.