ZOOPLANKTON AND PHYTOPLANKTON IN ALL ANOXIC LAYERS OF LAKE FUKAMI-IKE

Lake Fukami-ike is a small monomictic and eutrophic lake, located in southern Nagano Prefecture in Central Japan. An uncommon phenomenon of dissolved oxygen 0-1 mgL -1 from the surface to the bottom layer occurred on 16 November, 2013. On November 2, Trichocerca similis (Rotatoria) etc. dominantly distributed from 0-5 m depth depending on distribution DO concentration. Tintinnopsis lacustris (Protozoa) was found in the bottom layer (anoxic condition). The number of cells (Fragilaria rumpens (Bacillariophyceae) etc. abounded from the 0-5 m layer. On November 16, T. lacustris distributed from the surface to the bottom layer. Then, T. lacustris continued to distribute from the surface to the bottom layer, and the genus Synedra was found to have distributed uniformly from the surface to 6 m depth in the next investigation on 21 December, when the DO concentration was about 10 mgL -1 from the surface to the bottom layer. The changes in vertical distribution of T. lacustris, seemed to indicate that lake water was lifted from the bottom layer when shift stagnation periods to circulation periods.