Abstract
Most of the submergent vegetation in Lake Kasumigaura, Japan, has disappeared due to eutrophication, the construction of concrete embankments, and the artificial control of water levels. However, some propagule banks remain and include several species of submergent macrophytes. We investigated whether submergent macrophytes could be regenerated from propagule banks if they were protected from fish. Four fish-free enclosures were installed in the littoral zone of Takahamairi Bay, Lake Kasumigaura, in July 2002. Two weeks later, the density of crustacean zooplankton had increased to >500 individuals l^<-1> , chlorophyll a concentrations had decreased, and transparency had increased. By one and a half months after installation, however, both the density of crustacean zooplankton and the transparency had decreased. The macrophytes Potamogeton malaianus, Hydrilla verticillata, Elodea nuttallii, Egeria densa, and Trapa japonica emerged in all enclosures. Therefore, we suggest that fish-free enclosures may be useful for restoring submergent macrophytes in the littoral zone of Lake Kasumigaura.
