Aquatic Mosses on Cobble in Riffles and Those Resistance to Disturbances due to High Flow and Sediment Implement

The growth of aquatic mosses attached on a cobble in riffles was confirmed in a river in Japan. Cover of the aquatic mosses reduces the biomass of attached algae which is the source of energy of a commercial fish. This study aims to understand how the aquatic mosses keep their coverage on the riffles from the viewpoint of the response to flood disturbances. The resistance to disturbances due to water flow and sediment impingement on the mosses is investigated through a laboratory experiment. It is observed that the intermediate impact seems to remove the silt in the biofilm, but the majority of the mosses sustains the coverage. Based on the visual inspection of the moss cover after the experiment, the remaining moss mainly consists of short fresh stems. Generally, the mosses seem well adapted to the high-speed flow environment typical in riffles.