Studies on the interstitial animals in the Ishikari beach, Hokkaido, northern Japan-A preliminary report

Abstract

General patterns of the microdistribution of some interstitial animal groups are described as a preliminary report from the studies on the interstitial fauna and the bionomics of harpacticoids, which have been carried out at the Ishikari beach on the Japan Sea coast of Hokkaido. The Ishikari beach is characterized by homogeneous medium fine sand and small tide. Vertical distribution of nematodes are examined in order to estimate the difference between the density as represented by the number of individuals per unit sample volume and that per unit pore water volume by using the method formerly elaborated by the author. Characteristics in the microdistribution of Hesionides arenaria (Polychaeta) and Hypsibius itoi (Tardigrada) and five species of Harpacticoida are discussed. Distribution range of Arenopontia ishikariana, that is the dominant species in this beach (the maximum density recorded 4045 individuals per 100 cc sand sample), is very wide both horizontally and vertically, extending from the foreshore to the backshore. Nodtiella sp. penetrate into the backshore a little above the ground water level. Arenosetella bidenta and Leptastacus japonicus occur within well wet sand of the foreshore, and do not penetrate into the backshore. Paraleptastacus unisetosus are restricted in deep layers of the backshore during the summer, but appear in the upper foreshore during a short period of the early spring. This change of the microdistribution of P, unisetosus suggests a seasonal migration.