Understanding the recent range expansion of the hermit crab, Clibanarius erythropus, to the British Isles through larval dispersal models and phylogeographic analysis

Abstract

As climate change progresses, the ranges of many species will begin to shift. Which species will have their ranges shifted and where, will have major consequences for conservation, habitat management, agriculture, and human health. This thesis furthers our understanding of the processes that limit and facilitate range expansion by investigating the appearance of the hermit crab Clibanarius erythropus to the southwest United Kingdom (UK). Evidence suggests that C. erythropus arrived in the southwest UK via the species’ pelagic larvae drifting on ocean currents. The Mer d'Iroise, the historical limit of C. erythropus’ range, is a biological transition zone where the warm-water species found in the Bay of Biscay transition to the colder-water species of Northern Europe. Consequently, C. erythropus may be one of the first of many species whose range will expand to the southwest UK in the future. In chapter one, we study the phylogeographic structure of C. erythropus across its historic and newly established range. C. erythropus is a rare example of panmixia in the European seascape, indicating that populations of C. erythropus are interconnected and that the species has overcome most barriers to gene flow seen in other intertidal species. Panmixia suggests that the range of C. erythropus can readily shift with environmental change. In chapter two, we investigate the oceanographic processes that facilitated the transportation of C. erythropus to the UK. Using a hydrodynamic model, we simulate the dispersal of C. erythropus larvae in the English Channel over a number of years. Simulations suggest the larvae of C. erythropus arrived in 2014, originated from North Brittany, experienced a mean temperature of around 16 °C, and took longer than 20 days to be transported across the English Channel. Our results suggest that the transportation of larvae from Brittany to the southwest UK is rare and driven by the stochasticity of ocean currents which could limit the ability of many species to adequately shift their range to the UK with climate change.