Characteristics of the bottom sediments inhabited by the surf clam Spisula sachalinensis in Sendai Bay.

Abstract

Bottom sediments of Isobe Ground in southern Sendai Bay were analysed to clarify the factors affecting living conditions of the surf clam. The sediments were mostly composed of sand, and the surf clam lived in well-sorted fine to very fine sandy bottoms with less organic matter, shallower than 12-15m deep. They were distributed in a shoaling wave zone between the breaker zone and the wave base.The surf clam seemed to depend on hydrodynamic conditions responsible for sediment properties rather than on the sediment itself. Since the surf clam feeds primarily on suspended rather than deposited material, bottom water movement great enough to supply suspended organic matter constantly, may be an important factor, causing the surf clam to be concentrated in the shoaling wave zone.Sediment with larger particles that hinders burrowing, or increased mud content causing insufficient supply of food negatively influence the distribution of the surf clam. The surf clam may also be affected by the rough waves in the surf zone.