To cope with seawater degradation in public waters, it is fundamentally important to grasp the behavior of nutrients and organic substances involving mutual action of ecosystem and biological activity.
　Aiming to develop the microcosm test, basic investigation of designing microcosm copntainer and experimental procedures were performed, and application test was executed in the bay of Tokyo. The container is of 1 meter in diameter and 5 meters in length, and covered with transparent vinyl sheet. htis container was installed for 5 to 10 days in the day. The relation between phytoplankton and zooplankton, and the relation with nutrients were qualitatively observed, and several problems to the test and future subjects were pointed out.