Photographic records of land hermit crabs (Decapoda: Anomura: Coenobitidae) using beach debris as shells on Ishigakijima and Takarajima islands, Japan

Abstract Land hermit crabs generally use gastropod shells but sometimes occupy beach debris. We report photographic records from Ishigakijima and Takarajima islands, Japan. On Ishigakijima, Coenobita rugosus, C. brevimanus, and C. cavipes were found using a plastic cap, plastic bottle, polyvinyl chloride socket, and a coconut crab chela. Among 176 individuals of C. purpureus recorded on Ishigakijima, none occupied beach debris, whereas nine of 276 individuals (3.3%) on Takarajima were found using plastic caps, a metal socket, or a glass bottle. Most C. purpureus on Takarajima had a shield length of <11 mm, and approximately half occupied small land snail shells, while individuals carrying debris appeared to belong to larger size classes (>11 mm). In contrast, most C. purpureus on Ishigakijima exceeded 16 mm in shield length, and none occupied small land snail shells. The higher incidence of debris use on Takarajima may be related to local differences in shell use and size structure among populations.