Abstract
Seasonal variation in the species composition and abundance of epilithic algal community on a rock located at the upper littoral area in the north basin of Lake Biwa was investigated. Schizothrix sp., Calothrix parietina and one species of Pleurocapsaceae were always found at the splash zone of a rock. It seemed to indicate that those Cyanophyceaen algae were tolerant to desiccation and/or high energy of solar radiation including high UV-radiation. The dominated taxa and algal biomass in the epilithic algal community underwater zone changed seasonally and vertically during the investigation period. Spirogyra sp. (Chlorophyceae) increased from February and occupied a greater part of total algal biomass until July. In August and October, algal biomass was extremely low, in which Calothrix parietina and Homoeothrix janthina were dominated. Diatom such as Cymbella turgidula dominated through low temperature season. Numbers of diatom taxa actually increased during the occurrence of marked growth of Spirogyra. It seemed to be related to the geo-morphological complexity caused by the presence of the large filamentous algal biomass.
