Abstract: Acomprehensive oceanographic survey was made in the East China Sea (122°～123°30′E,29°～32°N) during April to May, 2002, and the zooplankton samples were collected by zooplankton net (mesh size 0.567mm).Analyses on the ecological characteristics of zooplankton such as its quantity, community characteristics, species composition and dominant species showed that 128 species of diet zooplankton were identified (16 pelagic larvae and fish juveniles were not involved). Among them, copepods occupied dominant position, including40 species, composing31.25% of diet zooplankton. The community was divided into 3 ecological types, in which,eurythermy and euryhalinity occupied dominant position. Key species,Calanus sinicus, was the first dominant species (142.10 ind·m^-3, composing68.09% of diet zooplankton abundance). The average biomass of zooplankton was 243.80 mg·m^-3 (55.53～773.92mg·m^-3),and the highest density (>500 mg·m^-3) was found in the estuary area of the Yangtze River (30°45′～31°15′N, 122°45′～123°15′E). The average biomass of diet zooplankton was 195.96 mg·m^-3 (55.53～496.09 mg·m^-3). It was also showed that the biomass value of the estuary area of the Yangtze River (the north of 30°30′N ) was higher than that of the southwest of Zhoushan waters,and that of the offshore of the estuary area of the Yangtze River (122°45′E) was higher than that of coastal waters.The mean value of diversity index (H′) was 2.12 (1.09～3.73), and the stations having low H′(<2) occupied 37.03%.The index of diversity, evenness and richness in the estuary area of the Yangtze River were low, but dominance was high. These results showed that the community structure of zooplankton in studied areas was not stable. Regression analysis results showed that main factors in relation to the characteristic distribution of zooplankton were temperature, diatom abundance, and dinoflagellate abundance.

Key words: Zooplankton, Ecological characteristics, Spring, East China Sea, Red tide