Abstract
Examining riffles of the Tama River, benthic algal biomass' relation to movement of stones on a streambed of Nagata in the Tama River was investigated experimentally. Effects of the stone size on algal development were particularly examined. Several new stones from five diameter classes were marked with colored paint and submerged in a limited area. For 43 days, we counted the stones that had moved into and out of the original area in reference to the stone size differences. The algal biomass on all stones in the original area was measured on the final day of this experiment. The fraction of stones moved by current increased concomitantly with the increased flow discharge. Small stones were moved more easily than large stones. The algal biomass on them was less because most small stones had a short stable duration. The duration of stability of streambed substrata, which is strongly correlated with the stones' size, is an important determinant of algal development. Furthermore, positive correlation between the stones' size and benthic algal biomass was also indicated about stones remaining for 43 days. In microhabitat, small stones had the greater influence of the disturbance by the water current and the moving stones from upper streams.
