Abstract
The physicochemical conditions and the species composition of plankton in Fukuji Reservoir on Okinawa Island, which has a subtropical climate, were investigated for about a year-long period covering the main seasons from June 1980 to February 1981.
In the summer thermal stratification was markedly developed, but was not observed in winter. The water temperature was considered to form the various limnological characteristics in the reservoir. With respect to plankton, 17 genera and 38 taxa were recorded from the fixed station. Green algae were the most abundant plankton in the summer, and diatoms developed profusely in the winter. The zooplankton were surprisingly few in both number and species during the winter. The development of plankton in the summer was found to he associated with the abundance of inorganic nutrients such as NH4+ and PO43-. According to Hutchinson's classification, the Fukuji Reservoir seems to fall into the plankton group X (mesotrophic or eutrophic desmids).
