Studies on the coastal environment in Lake Biwa. I. Species composition and distribution of submerged macrophytes

Abstract

In summer of 1997, submerged macrophytes were investigated in 6, 354 quadrats (10 m × 2 m) along 104 transects covering the whole littoral zone of Lake Biwa by SCUBA diving to obtain a quantitative view of species composition and horizontal and vertical distributions of respective species. Twenty three species were found in this survey. The species with a high frequency were Potamogeton maackianus, Hydrilla verticillata and Elodea nuttallii. The vegetation was classified into four types by cluster analysis using values of similarity index among all transects. Four types were as follows: west and north (N1), north-east (N2), south-east (N3) in Northern Basin, and Southern Basin (S). N2 type had the largest vegetational cover, cover layer, number of species and diversity index, and N1 type the smallest number of species. Applying the principal component analysis for Northern and Southern Basins, the richness of vegetation could be reasonably ordinated by the first principal component. The groups of species growing in different environmental conditions (wave energy, water depth, transparency and grain size) were also interpreted by the second and third principal components.Scatter diagrams for water depth and grain size of submerged macrophyte species showed the characteristic of habitat conditions in each basin, indicating higher habitat diversity in Northern Basin than in Southern Basin. Differences in vertical distubution patterns of some species between the basins were discussed in relation to the growth form, interspecific competition and environmental change (eutrophication, etc.). Influence of water level fluctuation on submerged macrophyte species was also discussed in the context of a possible low-water level (B.S.L. -1.5 m) in the Lake Biwa Development Project.