GROWTH, BREEDING, AND RECRUITMENT IN SCOPIMERA GLOBOSA AND ILYOPLAX PUSILLUS (CRUSTACEA : OCYPODIDAE) IN THE ESTUARY OF WAKA RIVER, MIDDLE JAPAN

Abstract

Field studies were conducted on the growth, breeding cycle and recruitment of the two ocypodid crabs Scopimera globosa De Haan and Ilyoplax pusillus De Haan, in the estuary ofWaka River (34°l0'N 135°10'E). The sexual behaviors were observed from April through August in S. globosa and from May through August in I. pusillus. The ovigerous females of S. globosa were found from April through August and those of I. pusillus from May through September, being most abundant in June in both species. The newly settled juveniles were most abundant in August in both species, showing the occurrence of the most intensive settlement from July to August. The recruitment sites almost coincided with the adult habitat in both species. In I. pusillus the recruitment intensity was relatively higher at the area of higher adult density. But in S. globosa, it was higher at the area of lower silt-clay content in the bottom surface sediment in comparison with the area of higher silt-clay content, while the density of the larger adults tended to be relatively higher at the latter area, which indicates the shift of the main habitat in relation to the substratum with growth. The females of both species and the males of S. globosa commenced to breed in the second summer of their life, but many of the males of I. pusillus were suspected to breed in the third summer for the first time. It appeared that I. pusillus and the males of S. globosa overwintered two times at least after settlement, whereas in the females of S. globosa the overwintering in their second year was doubtful. These specific differences suggest that S. globosa has a slightly shorter longevity and a slightly earlier maturation than I. pusillus.