Study On The Macro-zooplankton And Meso-zooplankton Community Ecology In The North Yellow Sea In Summer And Winter

Zooplankton community structure and its influencing factors were studied by means of multi-variable and bio-environmental analysis based on the samples collected in the North Yellow Sea (NYS) during two survey cruises conducted separately in summer (Jul. 2006) and winter (Jan.2007). Zooplankton diel vertical migration (DVM), distribution and their relations to environmental factors were analyzed in L02 station. The research can provide important fundamental information for the long-term monitoring of zooplankton ecology in the North Yellow Sea.A total of 113 zooplankton taxa and 27 pelagic larvae were identified during two surveys, and they belonged to Protozoa, Cnidaria, Ctenophora, Mollusca, Arthropoda, Chaetognatha and Urochordata. Crustacea and Cnidaria were the most abundant two components of the zooplankton. The species number of pelagic crustacean represented above 33% of total species richness and copepods were the most dominant crustacean in surveyed waters.During summer, the mean abundance value of zooplankton was 525.1ind/m3. The abundance in the inshore of Shandong and the middle part of NYS were higher than that in Liaotung peninsula waters. In winter, the mean abundance value of zooplankton was 263.8ind/m3. The abundance in Liaotung peninsula waters was higher than that in the inshore area of Shandong and the middle part of NYS. Calanus sinicus was the most important dominant species in the NYS. Both Acartia clausi and Sagitta crassa were the dominant species in two seasons.In summer, the mean biomass was 570.1mg/m3. The biomass was higher in the southeast part of surveyed area than that in the inshore area of Shandong peninsula and in Liaotung peninsula waters. In winter, the mean biomass was 297.7 mg/m3, the biomass in Shandong peninsula waters and the eastern part of the surveyed waters were lower than that in Liaotung peninsula waters.Four groups were distinguished by the cluster analysis method, based on the species composition and abundance of zooplankton. They are:ⅰ)GroupⅠlocated in C1001 station was dominated by Turritopsis nutricula, Corycaeus affinis, Sagitta crassa, Macrura larvae and Brachyura zoea, which only appeared in summer;ⅱ)Liaoning neritic oligohaline Group. In summer the dominant species were Evadne tergestina, Calanus sinicus, Paracalanus parvus, Centropages abdominalis, S. crassa, Oikopleura longicauda, and Macrura larvae and fish-lavae were also dominant in the Group, in winter, the dominant species were C. sinicus, P. parvus, Acatia clausi and S. crassa;ⅲ)Yellow Sea Cold Water Mass Group. It was dominated by C. sinicus, P. parvus, Centropages abdominalis, A. clausi, Themisto gracilipes, Euphausia pacifica and S. crassa in summer, while in winter, the dominant species were C. sinicus, P. parvus, A. clausi, E. pacifica and S. crassa; GroupⅣlocated in Shandong peninsula, dominated with C. sinicus, S. crassa, Echinopluteus larvae and Ophiopluteus larvae in summer, and in winter the dominant species were C. sinicus, P. parvus, Centropages abdominalis, Corycaeus affinis and S. crassa. Salinity and temperature in bottom were the most important abiotic factors for the zooplankton distribution and community classification in summer, while in winter, surface salinity and phytoplankton abundance were the primary factors which influenced the zooplankton distribution and abundance in the surveyed waters.In summer, the mean Shannon-Weaner Diversity, Pielou′s evenness and Margalef species richness were 2.15, 0.45 and 4.74, which were higher in the inshore than in the middle and western part of the surveyed waters. And in winter, the values were 1.97, 0.48 and 3.40, respectively; the values in northern waters of Shandong peninsula, and eastern part of the NYS were higher than that in inshore of Liaotung peninsula, middle and western part of the surveyed area.Due to the marked diel vertical migration, the abundance of zooplankton in each layers were not even in summer. Zooplankton was dominated by Calanus sinicus, Paracalanus parvus, Acartia clausi, Oithona similis, Sagiita crassa and Copepod nauplius were dominant in L02 station. Thermocline in cold water mass was the most important factors that influenced zooplankton diel vertical migration (DVM). In winter, the abundance of zooplankton in each layers were even, and diel vertical migration (DVM) were unmarked. The dominant species in winter were approximately same as in summer. Zooplankton diel vertical migration (DVM) could be divided into two types: marked and unmarked which the latter could also be divided two types: the upper layer level and the middle lower level.