The status of Clibanarius erythropus after a recent range expansion to Great Britain, with the highest latitude recording of a gravid individual

In 2016, the range of the hermit crab Clibanarius erythropus expanded to South West Britain for the second time. C. erythropus primarily lives in the Mediterranean and the Atlantic coast of Europe from the Bay of Biscay to Morocco. The species has now been recorded on both the north and south coast of the South West peninsula of the UK from Newtrain Bay, on the north coast of Cornwall, to Wembury, on the south coast of Devon. It is unknown if the crab’s reappearance in the UK has been caused by a one-off colonisation event or by a continued influx of larvae. The population in the UK is made up of individual within a narrow size bracket, indicating a single colonisation event took place, and that the population is an ageing one. However, we also report the highest latitude recording of a gravid individual for the species. A lack of gravid individuals was suggested to be why the species was unable to sustain its presence in the UK following a previous colonisation in 1960. This discovery hints that rising water temperatures may allow C. erythropus and other warm-water species to expand and sustain themselves in the UK. We also found crossover in shell utilisation between C. erythropus and the native hermit crab Pagurus bernhardus, suggesting that competition might occur between the two species.