| Based on the data obtained from the two cruises carried out in the North Yellow Sea (NYS) during spring and autumn 2007, the species composition, quantitative distribution and seasonal variation of zooplankton in the NYS were analyzed. The vertical distribution and diel vertical migration (DVM) of zooplankton were analyzed in L02 station, so was their relations to environmental factors. Zooplankton biodiversity, community structure and its dominant species were analyzed with multivariate analysis method. The purpose of this research is to provide fundamental information for the long-term monitoring of zooplankton ecology in the North Yellow Sea.Totally 80 species of adult zooplankton and 26 groups of planktonic larvae were identified. The adult zooplankton species belong to Protozoa, Cnidaria, Ctenophora, Annelida, Mollusca, Arthropoda, Chaetognatha and Urochordata, respectively. Copepods and planktonic larvae were of the first two largest species richness, followed by medusa. The species of zooplankton in spring were more than that in autumn. Obvious seasonal succession was observed for dominant species. Calanus sinicus was the most dominant species of zooplankton in the studied area in spring while Sagitta crassa in autumn. Both Calanus sinicus and Sagitta crassa were the dominant species in the two seasons.Seasonal variations of zooplankton distribution were obvious. The abundance of zooplankton in spring were much more than that in autumn, but the zooplankton distribution were more even in autumn. During spring, the mean abundance value of zooplankton was 816.93 ind/m3. The abundance in the inshore of Shandong and Liaotung peninsula waters were higher than that in the middle part of NYS. In autumn the mean abundance value of zooplankton was 355.27 ind/m3. The abundance in Liaotung peninsula waters was higher than that in the inshore area of Shandong and the middle part of NYS.During spring, the mean biomass of zooplankton in surveyed area was 700.69 mg/m3. The highest zooplankton biomass appeared in the southeast part of surveyed area, followed by the inshore area of Shandong peninsula and Liaotung peninsula waters, while the middle part of NYS had the lowest zooplankton biomass. During autumn, the mean biomass was 171.83 mg/m3, the biomass was higher in the inshore area of Shandong peninsula waters than the other part of surveyed area.In spring and autumn, the abundance of zooplankton in each layers were even, and diel vertical migration (DVM) were unmarked. The result shows that diel vertical migration of the zooplankton in that area can be divided into two types:marked and unmarked. The former consists of some large species, the latter consists of some smaller species. In addition, the vertical distribution of the zooplankton can be divided into two levels generally:the upper layer level and the intermediate-lower level.According to the zooplankton species composition and abundance at each station, four groups were distinguished for the total stations by using the method of cluster analysis. Group I located in the inshore area of Liaotung peninsula. It was influenced by the Yalu River diluted water. In spring, the species which have high contribution were Calanus sinicus, Acartia clausi, Centropages abdominalis, Sagitta crassa. In autumn, they were S. crassa, C. sinicus, Paracalanus parvus. Group II located in the inshore area of Shandong peninsula. In spring, the species which have high contribution were C. abdominalis, Oikopleura dioica, A. clausi, C. sinicus. In autumn, they were S. crassa, P. parvus, Pleurobrachia globosa. GroupIII located in the middle part of NYS, influenced by the Yellow Sea Cold Water Mass. In spring, the species which have high contribution were C. sinicus, C. abdominalis, A. clausi. In autumn, they were S. crassa, C. sinicus, O. longicauda, Doliolum denticulatum, P. parvus. GroupIV located in the southeast part of NYS, which only appeared in spring. The species which have high contribution were C. sinicus, Salpa fusiformis, S. crassa, Oithona plumifera. In spring, the mean Shannon-Weaner Diversity, Pielou's evenness and Margalef species richness were 2.1,0.5 and 2.3, which were higher in the inshore of Shandong peninsula and east part of NYS than the the inshore of Liaodong peninsula and middle part of the surveyed waters. And in autumn, the values were 2.6,0.5 and 3.5, respectively; the values in the inshore of Liaotung peninsula and the southeast part of the NYS were higher than the other areas.The study of the taxonomic diversity of planktonic copepod communities shows that there are 44 species of planktonic copepods, belong to 4 orders,14 families and 44 generas, recorded in the North Yellow Sea. The theoretical mean value of the average taxonomic distinctness (Δ+) based on the North Yellow Sea planktonic copepod master list is 82.2. During the investigation, the taxonomic diversity(Δ) and taxonomic distinctness(Δ*) were higher in Autumn and Winter than summer and spring, and the average taxonomic distinctness was higher in summer and spring than autumn and winter. The spatial distribution of the four indexes showed significant differences among sampling stations, however, the average taxonomic distinctness of the 4 seasons were all included in the funnel plots with 95% confidence limits.
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