Abstract
Spatial distributions of the biomass and species composition in submerged macrophytes in the southern basin of Lake Biwa were surveyed in September, 2002. Macrophyte samples were collected from 52 sites by SCUBA. The total biomass (dry weight) of and the vegetated area of macrophytes in the southern basin during the study period were estimated as 10735 ± 3030 t, and 43 km2, respectively. Potamogeton maackianus was dominant, and Hydrilla verticillata, Ceratophyllum demersum, Egeria densa and Myriophyllum spicatum were also abundant in the basin. Biomass of these five species accounted for 99% of the total macrophyte biomass. P. maackianus and C. demersum showed high niche overlap (Pianka's α =0.71). Biomass of P. maackianus was positively correlated with the average transparency/water depth ratio (Spearman's ρ =0.50), suggesting that P. maackianus tended to grow at the bottom under strong light. Biomass of C. demersum showed a positive correlation with transparency (ρ =0.44). Biomass of E. densa was negatively correlated with the sediment diameter (φmean) (ρ =-0.40). The quantitative composition of macrophyte species in 2002 was quite different from that of 1936 when macrophytes were flourishing in the southern basin.
