Abstract
The structure of a submerged macrophyte community (vegetation cover, species richness and species composition) and the seasonal changes were investigated at the littoral zone (< 6 m deep) of a calm bay in Northern Basin of Lake Biwa, Japan, where the transparency is high and no waterfowl grazers exist. To evaluate the effect of a small difference in depth profile on the community structure, the vegetation map of 35 m-belt transect (4 m wide) was made monthly at two sites (30 m apart) between March and November 1997. In total, the same 11 species were observed in the two sites, including two alien species, Egeria densa and Elodea nuttallii, and an endemic species, Vallisneria biwaensis. There was no significant difference in species richness in a census between the two sites. The species zonation was unclear in both sites: various mixed species patches were found throughout the study period. There were differences in the growth patterns of five species between the two sites. In a calm and clear-water littoral zone, where there is no disturbance by wave action, a small difference in depth profile can affect the growth patterns of several macrophyte species and then affect the three-dimensional structure of the macrophyte community, which can be a crucial determinant of the habitat structure of small aquatic animals.
