Temporal Change in Density and Size Structure of the Sea Cucumber Polycheira rufescens Inhabiting the Intertidal Boulder Beach at Hatakejima Island, Tanabe Bay, Central Japan

Abstract

A field population study of a holothurian, Polycheira rufescens, conducted at an intertidal boulder beach of Hatakejima Island in Tanabe Bay, central Japan, revealed that the temporal change in density varied with site and the density tended to be positively correlated with the abundance of small boulders of 10-20 em length. Size frequency distribution was uni-modal and the peak remained at a constant size class irrespective of the season, but shifted to a smaller size class in a winter month. Size structure was similar in spite of higher and lower tide levels. The number of individuals occurring under a boulder tended to increase with boulder size. The mean body size of individuals under small and large boulder was not different in most cases.