Algal Community Structure in a Littoral Zone in the North Basin of Lake Biwa.

Abstract

Seasonal variations in the biomass and species composition of benthic and planktonic algal communities were investigated from June 1994 to April 1996 in a littoral zone with gravel in the north basin of Lake Biwa. Seasonal fluctuations in biomass were mainly brought about by the rise and fall of a filamentous green alga (FGA) Spirogyra sp. in the benthic algal community, together with Closterium aciculare, Staurastrum dorsidentiferum and Gomphosphaeria lacustris in the planktonic algal community. Comparing the benthic with the planktonic algal biomass, the former made up over 90% of the total algal biomass. This result suggests that the benthic algal community contributes highly to primary production in the littoral zone. There were extraordinary differences in the vertical-distribution pattern and lightextinction coefficient between the FGA and sessile algae (benthic algae except FGA) forming the benthic algal community, thus dividing it into two components : FGA, and sessile algal communities. From the viewpoint of the productive structure of the algal community in the littoral zone, we propose that the community should be regarded as a three-component structure of planktonic, FGA, and sessile algal communities.