Temporal And Spatial Variation And The Main Driving Forces Of Zooplankton Community In The Yangtze River Estuary

Based on the historical data of zooplankton community survey in May(spring)and August(summer)in the Yangtze River Estuary from 2006 to 2008 and 2016 to 2018,this study analyzed the temporal and spatial variation characteristics of zooplankton community structure and key ecological parameters in the Yangtze River Estuary by using multivariate analysis methods such as community cluster analysis,ANOSIM analysis,SIMPER analysis and Canonical Correspondence Analusis.Through in-depth studied of the relationship between zooplankton abundance,important ecological parameters,dominant species and environmental factors,this paper discussed the main driving factors of zooplankton community change in the Yangtze River Estuary.The main results include the following aspects:1)The results of principal component analysis of environmental factors showed that the environmental factors that had a great impact on the investigated sea area include water temperature,salinity,dissolved oxygen and inorganic nitrogen.2)Totally 109 species were identified,belonging to 5 phyla and 14 categories.There were 70 species in spring season and 83 species in summer season respectively.The results of Kruskal Wallis test showed that the number of species of groups did not change significantly between seasons and investigation stages(P > 0.05),but the number of species of stations in different investigation stages in the same season changed significantly(P < 0.05).The dominant species of zooplankton in the Yangtze River estuary were mainly copepods.In spring,they were mainly Tortanus vermiculus,Labidocera euchaeta,and in summer,they were mainly Acartia Pacifica,Labidocera euchaeta and Schmackeria poplesia.3)Zooplankton abundance had obvious temporal and spatial changes.In spring,zooplankton abundance showed the characteristics of slightly higher coastal stations and slightly lower offshore stations.The high value area was generally outside the North guide dike(station 3)and the sea area near the mouth of Hangzhou Bay(station 7).Compared with the high abundance area of zooplankton in spring,the center of gravity moves to the open sea in summer,which was generally concentrated in the adjacent waters of the rugged archipelago Jigu reef line.The abundance of zooplankton in summer was higher than that in spring,and the abundance in spring and summer of 2016-2018 was lower than that in the same period of 2006-2008.The results of Kruskal Wallis test showed that there was significant difference in abundance between different investigation stages in the same season(P < 0.05),but there was no significant difference in zooplankton abundance in the same investigation stage and season.The abundance of zooplankton dominant species also had certain spatial distribution characteristics.4)The results of community clustering showed that the zooplankton community of the year from 2006 to 2008 could be divided into three groups including group I(offshore community),group II(the Yangtze River Estuary water community)and group III(community in salt and fresh water interlaced waters).Two groups were clustered in the year from 2016 to 2018 including group IV(community in salt and fresh water interlaced waters)and group V(community in Yangtze River alluvial and fresh water control area).According to the spatial characteristics of clustering group,two groups of sites were summarized which named near estuarine group and south estuarine group,respectively.The contributing species of the similarities and dissimilarities among groups,seasons and stages were analyzed and discussed.The community of zooplankton in the Yangtze River Estuary could be characterized by the community of Tortanus vermiculus and Labidocera euchaeta in spring season,and that of Acartia pacifica-Labidocera euchaeta in summer season.The water temperature and salinity might be the key environmental indicators that affecting the temporal and spatial variations of zooplankton in the Yangtze River Estuary.5)The key ecological parameters of zooplankton had obvious temporal and spatial variation characteristics.In spring,there was a very significant negative correlation between zooplankton abundance and Shannon Weiner diversity index,evenness index and richness index,and a positive correlation between the three indexes;In summer,the correlation between abundance and the three indexes is unstable,and only Shannon Weiner diversity index and evenness index showed a very significant positive correlation among the three indexes.6)The results of GAM model analysis showed that water temperature,salinity and chlorophyll a were the main environmental factors affecting zooplankton abundance,while water temperature,salinity,dissolved oxygen,ammonia nitrogen and chlorophyll a were the main factors affecting the abundance of main dominant species.CCA analysis showed that from 2006 to 2008,the main environmental factors affecting zooplankton community structure were water temperature,salinity and dissolved oxygen;From 2016 to 2018,the main environmental factors affecting the community structure of zooplankton were water temperature,salinity,nitrate and inorganic nitrogen.