HABITAT USE AND ACTIVITY PATTERNS OF THREE JAPANESE FRESHWATER CRABS OF THE GENUS GEOTHELPHUSA (DECAPODA, BRACHYURA, POTAMIDAE)

Geothelphusa dehaani (White, 1874) is sympatric with G. exiguaSuzuki and Tsuda, 1994, in Ohsumi Peninsula and with G. marmorataSuzuki and Okano, 2000, in Yakushima Island, southern Kyushu, Japan. Geothelphusa dehaani is widely distributed in Japan, whereas G. exigua and G. marmorata are endemic in riverine habitats at their respective locations. Visual and trapping surveys were conducted to examine the habitat preference and elucidate the factors maintaining sympatry among the three species. Results showed that G. exigua and G. marmorata are mainly aquatic, whereas G. dehaani is amphibious. Geothelphusa dehaani is more associated with land habitats under sympatry but equally extends in water and on land when singly constituting a population. All species exhibit varying degrees of nocturnalism, but G. marmorata is more active at night than either G. dehaani or G. exigua. Differences in habitats and activity patterns among the Geothelphusa species were attributed to their microenvironments and the effects of interspecific competition under sympatry.