Studies On Zooplankton Community And The Effects Of Environmental Factors On Its Distribution In The Southern Yellow Sea

Zooplankton is the principal secondary producer in the marine ecosystem andplays a pivotal role in the marine food chain (web) as a connecting link between thepreceding and the following. Its distribution is impacted by the oceanic conditions,such as temperature, salinity and ocean current. Meanwhile, it is controlled by thebottom-up and top-down effects in the marine food chain. Therefore, the research onzooplankton is the foundation to understand the ecosystem function and dynamics inspecific sea area.Based on several field investigation data since2006, the temporal and spatialvariations and influencing factors of the zooplankton species compostion, abundance,biomass and diversity index were analysed; he effects of different sampling gears onzooplankton abundance, biomass and diversity index were analysed; the temporal andspatial variations of Salps and the effects of environmental factors on Salps werefirstly studied in the western southern YS; the species composition, seasonal alterationof dominant species of ichthyoplankton and the effects of different hydrographicalconditions in summer on the distribution of ichthyoplankton were analysed; theinternal structure of the Yellow Sea Cold Water Mass (YSCWM) on the distributionpattern of dominant zooplankton species were analysed; the influence of the YellowSea Warm Current (YSWC) on zooplankton biomass, the distribution warm waterspecies and the diel vertical migration of zooplankton before and after the occurrenceof YSWC were analysed. The main results are as follows:191zooplankton taxa and34pelagic larvae were identified in different seasonsin2006-2007. The species number of Cnidaria and Crustacea were the highest amonggroups. The zooplankton diversity was highest in autumn and lowest in summer. Thezooplankton diversity was closely correlated with the hydrographical phenomena. The diversity in summer was the lowest, which was correlated with the low diversity inthe YSCWM; in autumn, as the shrink of the YSCWM, the diversity increasedevidently and the area with high diversity was identical with the the sea area affectedby the Changjiang River Diluted Water (CRDW) and coastal current; the sea area withthe highest diversity was just where the YSWC intruded in winter; in spring, thediversity was also high in the sea area with residual water of YSWC.In spring, as the increase of water temperature and Chl a concentration, thezooplankton abundance and biomass were the highest; the abundance was the lowestin winter and the biomass was the lowest in autumn due to the low biomass ofgelatinous zooplankton.Differences were observed in the zooplankton abundance, biomass and diversitybetween different net types. The samples of large net severely underestimated theabundance of zooplankton with smaller size; the difference of biomass was less thanthat of abundance; the Shannon diversity, Pielou evenness index of the medium netwere higher than that of large net, but the Margalef richness index of the medium netwas lower than that of large net.The seasonal variations of Salps were studied systematically. Salpa fusiformisoccurred in winter, spring and summer in the southern YS, but totally disappeared inautumn. In summer, the high temperature and low Chl a concentration might be theprimary cause for the disappearance in autumn; the recurrence of S. fusiformis inwinter was correlated with strong period of YSWC and the population in the outercontinental shelf of the East China Sea. Doliolum denticulatum occurred in summerand autumn in the southern YS and became one of the dominant zooplankton speciesin autumn, which might be related with the long-term climate change.A total of58taxa of ichthyoplankton were identified in the yearly investigationsin the southern YS in2006-2007. The ichthyoplankton of different ecological typedominated as the season changed. For example, cold-water species Ammodytespersonatus dominated in winter and warm-water species Sillago sihama dominated insummer. In summer, the distribution patterns of the dominant ichthyoplankton,Engraulis japonicus and S. sihama were affected by the hydrographical conditions, such as tidal front, CRDW, Taiwan Warm Current.The YSCWM has significant effects on zooplankton distribution. In summer, theYSCWM provides refuge for the warm-temperate zooplankton species, such asCalanus sinicua and Euphausia pacifica to avoid the high temperature. Meawhile, thedistribution pattern of these dominant species might be affected by the internalstructure of the YSCWM, for example, the warm core might hold back the furthermigration of C. sinicus into the deep water area, in contrary, the cold water core mighthold back the shoreward migration of E. pacifica.In winter，the YSWC might affect the biomass, the distribution of warm-waterspecies and the diel vertical migration of zooplankton. The zooplankton biomass waslow in the sea area impacted by the YSWC; the warm-water species mainlydistributed in the sea area impacted by the YSWC; the diel vertical migration ofzooplankton was evident before the strong period of the YSWC, but the diel verticalmigration disappeared after the strong period of the YSWC.The variation of the hydrographical features might lead to the variation of thedistribution pattern of zooplankton. The distribution pattern of C. sinicus in the springof1959and2007was similar. But, the distribution pattern in summer had significantdifference in summer, which might be related with the variations of thehydrographical conditions, such as the coverage and strength of the Qingdao ColdWater Mass, the distribution of the tidal front and the variation of the strength of theCRDW.