STUDIES ON THE SUCCESSION OF BLUE-GREEN-ALGAE, MICROCYSTIS, ANABAENA,OSCILLATORIA AND PHORMIDIUM IN LAKE KASUMIGAURA

This study was conducted to examine and determine the factors affectin g dominance of the blue-green algal species of genus Microcystis, Anab aena, Oscillatoria and Phormidium from 1988 to 1990 in eutrophic Lake Kasumigaura. The algal dominancy of the three Anabaena species, A. aff inis, A. flos-aquae and A. spiroides, took place in early summer, whil e the dominance of the Microcystis species, M. aeruginosa, M. viridis and M. wesenbergii, took place from summer to fall. Water samples were collected at Tsuchiura Harbour in Lake Kasumigaura. The correlations between cell numbers of blue-green algal species and water qualities w ere investigated. The growth rates of algae in situ were determined. M . aeruginosa showed the highest increasing growth rate, while M. virid is was the lowest decay rate in the Microcystis species. M. aeruginosa exhibited high single correlations between water temperature, pH, tot al chemical oxygen demand (T-COD) and dissolved chemical oxygen demand (D-COD). The cell numbers of blue-green algal species were also compa red with each other to know any correlation. The high correlations bet ween the three Anabaena species were observed.