THE INTER-ANNUAL VARIATIONS IN NOCTILUCA SCINTILLANS ABUNDANCE AND EUTROPHICATION IN CHANGJIANG ESTUARY

Data gathered in eight seasonal oceanographic investigations in the Changjiang (Yangtze River) estuary (28°00'—32°00'N, 122°00'—123°30'E) in 1959 and 2002 were used to study the temporal-spatial distribution of Noctiluca scintillans in the waters, with which the ecological groups were classified using mathematical modeling. The impact of environmental factors on the eutrophication and the relation between eutrophication and the abundance of the species were studied. Clear seasonal variations in the abundance and occurrence frequency of N. scintillans have been recognized: very high abundance (48576.00ind/m3) and occurrence frequency (96.30%) in spring and low in other seasons; they assembled in spring, but scattered in other seasons. Salinity was shown a critical factor in determining the distribution in the estuarine waters, so did temperature as it inhabited coastal temperate zone in a narrow range of 15—20℃, best around 17.53℃. Notably, the abundance in spring of the estuary has been increasing significantly in recent years, resulted from eutrophication and caused HAB. Therefore, the species can be used to estimate eutrophication status.