和歌川河口干潟におけるヤドカリ類3種の夏期の分布と性比，体サイズ

抄録

In Japan, the hermit crabs Pagurus minutus, Diogenes nitidimanus and Clibanarius infraspinatus are common in inner bays, sandy tidal flats and shallow subtidal sediment, respectively. We investigated the distribution of these three species in summer at six sampling sites in the Waka-River Estuary, Wakayama Prefecture, Japan. The sampling sites were placed along the length of the estuary, with Site 1 situated high up in the brackish water of the estuary, Site 6 at the river mouth, and the other four sites at intermediate locations along the estuary gradient with the number of each site. Pagurus minutus was the dominant species at five out of six sites. Diogenes nitidimanus was mainly found at intermediate St. 3 and 5, relatively close to the river mouth, and had sandy substrates. Clibanarius infraspinatus was mostly found at St. 6. The sex ratio of D. nitidimanus was highly biased to males at St. 3 and to females at St. 5, while the sex ratio of the other two species did not vary across sites except for P. minutus at St. 4. Carapace and chelae length of males were larger than those of females in P. minutus for their right hands and in D. nitidimanus for their left hands, but not in C. infraspinatus for their right hands. In D. nitidimanus, small males were especially abundant at St. 3, while males of various size including large ones, were collected at St. 5. Females of various sizes were found at both sites. However, there were very few females at St. 3, while many females, including ovigerous ones, inhabited St. 5. The existence of the small male population distant from the reproductive population in D. nitidimanus may be an interesting aspect with respect to the life history strategy of the males and deserves further investigation.