Gastropod shell use by the land hermit crabs Coenobita brevimanus and C. cavipes in an abandoned village on Iriomotejima Island, Japan

Abstract

The aim of this study was to examine patterns of abundance, density, size, and shell use in Coenobita brevimanus and C. cavipes, occurring on Sakiyama Village, Iriomotejima Island, southwestern Japan. Crabs were captured and their body size and the type of adopted gastropod shell were recorded. Relative abundances were similar among species (67 and 64 for C. brevimanus and C. cavipes, respectively) and density of C. brevimanus was as high as 0.23 m⁻². Overall, C. brevimanus had larger body sizes (palm width 5.9–32.7 mm) than C. cavipes (4.2–14.2 mm). Patterns of gastropod shell use were also significantly different between species. While C. brevimanus used were the marine snails Turbo (Marmarostoma) argyrostomus and Mancinella armigera (each species comprised about 35% of all occupied shell), the most adopted gastropod shells by C. cavipes were the land snails Satsuma caliginosa caliginosa (38%) and Acusta despecta sieboldiana (19%). Interestingly, almost all (>90%) shells occupied by C. brevimanus were abraded, whereas for C. cavipes 56% of adopted shells were non-abraded. Generally speaking, C. brevimanus in Sakiyama, where the supply of artificial shells is relatively more limited than in more populated areas near to the village, had smaller body sizes, and occupied older shells.