Community Structure And Biodiversity Of Zooplankton In The Changjiang Estuary And Its Adjacent Waters

Community structure and biodiversity of zooplankton in the Changjiang (YangtzeRiver) estuary and adjacent waters were studied. This research was based on thesamples collected from150stations during four cruises from July to August in2006(Summer), December in2006to February in2007(Winter), April to May in2007(Spring), and October to December in2007(Autumn), respectively. Meanwhile, theadaption mechanism and responses of zooplankton community to the hypoxia in theChangjiang estuary were studied in combination with other environmental factors, and theresponse of the dominant groups of zooplankton including Medusa, Copepod,Amphipod, Euphausiacea and Chaetognatha to the climate change were also disscussedin an effort to explaining the effect of global warming on the distribution and abundanceof zooplankton main groups. The results are as follows:Firstly, seasonal variation of community structure of zooplankton in Changjiangestuary and adjacent areas were studied. A total of460species, belonging to246generaand7phyla with54categories of pelagic larvae are identified in the Changjiang estuaryand adjacent areas. The18groups of zooplankton include Hydromedusae,Siphonophora, Scyphomedusae, Ctenophora, Polychaeta, Cladocera, Copepoda,Ostracoda, Isopoda, Mysida, Cumacea, Amphipoda, Euphausiacea, Decapoda,Chaetognatha, Appendiculata, Thaliacea and Pelagic mollusca, among which copepod isthe most dominant group, followed by Medusa and amphipod. The community structureand biodiversity of zooplankton shows obviously seasonal variations. The dominantspecies of zooplankton have obviously seasonal succession phenomenon.The temporal and spatial distribution of abundance and biomass of zooplankton inChangjiang estuary and adjacent areas were analysed. The average abundance of zooplankton is the highest in summer with the value of378.1±376.6ind m-3, followedby321.8±535.1ind m-3,158.7±160.4ind m-3and15.5ind m-3in spring, autumn andwinter, respectively. However, the highest value of the average biomass of zooplanktonappears in spring with the value of368±565mg wwm-3followed by334±294mgwwm-3,180±176mg wwm-3and65±120mg wwm-3in summer, autumn and winter,respectively. The areas with high value of abundance all appear in the Changjiangestuary in spring, summer and autumn and decreases gradually from offshore to theopen sea for horizontal distribution, while in winter, the abundance of zooplanktondistributes evenly. The horizontal distribution of biomass shows the same variationtrend with abundance of zooplankton in spring and summer with the areas of high valueappearing in the Changjiang estuary and decreases gradually from offshore to the opensea. However, the distribution of biomass shows increas trend from offshore to the opensea in autumn. The area with high value appears in the east of Zhoushan archipelago,while in other waters, the biomass distributes evenly in winter. The temporal and spatialvariations of zooplankton show the same trends with chlorophyll a (Chl-a) and primaryproduction roughly.The results of taxonomic diversity of copepod in the Changjiang estuary show thatthe diversity index is the highest in autumn, followed by winter, summer and spring.While the biodiversity index (H’) of copepod is the highest in autumn and the lowest inwinter. Obviously, the taxonomic diversity index is different from traditional calculationdiversity index (H’), but the taxonomic diversity index can give more reasonableinterpretation on the biodiversity of copepod.Results of Pearson’s correlation analysis show that zooplankton is mainly related tosalinity, temperature, Chl-a, dissolved oxygen (DO), suspended particulate matter(SPM). Results of BIOENV show that in spring, salinity and SPM are the main factorsinfluencing community structure (Global R=0.821, p<0.01); In summer, salinity, depth,SPM and pH are the main factors influencing community structure (Global R=0.659,p<0.01); While salinity is the main environmental factor influencing communitystructure both in autumn (Global R=0.815, p<0.01) and winter (Global R=0.500,p<0.01). Based on the results of Pearson’s and BIOENV correlation analysis, it could be concluded that the main environmental factors influencing community structure ofzooplankton are salinity, temperature, SPM, DO and Chl-a.Secondly, a systematic study had been conducted on the temporal and spatialdistribution of major groups and key species of zooplankton in Changjiang estuary andadjacent areas. Results show that Medusa and Euphausiacea have similarly seasonalvariation trend, and the abundance is the highest in spring followed by summer, autumnand winter. The abundance of copepods and zooplankton were similarly trend inseasonal variation which is the highest in summer, followed by spring, autumn andwinter. The species number and abundance of Copepod have an ascend trend and thetwo warm-water species of Paracalanus aculeatus and Euchaeta concinna have becomethe dominant species of zooplankton in the Changjiang estuary waters, showing theirresponses to climate warming. The species number and abundance of Amphipod andChaetognatha show the similarly seasonal variation trend and the number of species isthe highest in summer, followed by autumn, spring and winter. The abundance andfrequency of occurence of Flaccisagitta enflata shows increasing obviously and theareas with high abundance of the population moving to the north, showing the responsesof Flaccisagitta enflata to the warming of marine environment in Changjiang Estuary.Finally, this paper is the first report on the community structure and biodiversity ofzooplankton in the habitats with hypoxia area of Changjiang Estuary, and the results areas follow: there are differences in the community structure of zooplankton betweenhypoxia area and adjacent waters, and the species percentage of copepod in hypoxiaarea are lower than that of adjacent waters. The biomass and abundance of zooplanktonin hypoxia area are higher than that of adjacent areas, with major links to the higherphytoplankton stock and primary production of surface in hypoxia area. There aresignificantly negative correlation between the biomass, abundance, biodiversity, speciesrichness and total species of zooplankton with DO in Changjiang estuary and adjacentareas.