Environmental Characteristics of the Habitats of Juvenile Sea Cucumber Apostichopus japonicus around Hokkaido

To specify the environmental characteristics of the habitats of juveniles of the sea cucumber Apostichopus japonicus (green-coloured type, small-sized individuals less than 60 g), field surveys were conducted mainly in the southern part of Hokkaido (Survey I). The juveniles were mostly found on stony bottoms that were shielded from waves-suitable habitats were from +0.4 (above a chart datum level) to -1.5 m deep. In areas where the stony bottoms were not shielded, suitable habitats were 2-20 m deep. Further, surveys were carried out in the intertidal boulder shore to specify the properties of the boulders underneath which the individuals were attached (Survey II). Individuals selectively used the large boulders that were rare in the study site, as well as used the boulders that fitted well into the depressions on the undulating gravel sediment (mostly of length less than 10 cm). The average size of the boulders to which two or more individuals were attached was 57,610 cm3 and to which four individuals (the maximum number observed in the present study) were attached was 74,256 cm3.