Population ecology of the hermit crab Clibanarius infraspinatus in the Waka River

MIYAGAWA Naoaki, KOGA Tsunenori

doi:10.5179/benthos.71.70

The hermit crab Clibanarius infraspinatus generally inhabits the infratidal zone and rarely occupies the intertidal area. However, at the mouth of the Waka River, they are commonly found in the intertidal sand flats located in the shallow channels, where we conducted quantitative surveys at six stations to investigate their population structure between June 2013 and May 2014. Between June and September 2013 and in May 2014 we collected, on average, 213 crabs per month. However, between December and March we found no crabs, which suggests that they migrated seasonally. Ovigerous females were found only between June and September, and their numbers were maximum in August accounting for 36% of all female crabs that were collected in that month. Males were larger than females in terms of body size distribution in the population. The shield length of the smallest ovigerous female was 5.9 mm. Chela size of males became relatively larger than that of females with their age. The right chela was slightly larger than the left one in females. The sex ratio in the population was nearly 1:1. In contrast to the lower four sites, fewer crabs and no ovigerous females were collected at the upper two sites. This may be because the substratum of the upper sites was muddy, differing from a typical habitat for C. infraspinatus. This along with the relatively fewer ovigerous females collected even in a peak reproductive season suggests that the tidal flat surveyed in this study may not be physically suitable for C. infraspinatus.

Population ecology of the hermit crab <b><i>Clibanarius infraspinatus</i></b> in the Waka River

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