Distribution and Factors Influencing Macro- and Meso-Plankton in the Yangtze River Estuary- East China Sea Continental Shelf in Summer

Abstract:

Based on the analysis of meso- and macro-plankton and water quality parameters from 17 stations in the Yangtze River estuary and adjacent regions in the summer of 2019， the present study investigated the spatial distribution patterns and major factors influencing meso- and macro-plankton. Under the influence of freshwater - seawater mixing in the Yangtze River estuary region， the species number and biodiversity indexes increased with increasing salinity in this transect， and the dominant species significantly differed among freshwater sites and low- and high- salinity sites. The density and biomass of meso- and macro-plankton in 13 stations of the typical transect along the Yangtze River estuary - East China Sea continental shelf showed no significant relationship with Chl-a， and significantly negatively correlated with the concentrations of nutrients， indicating that bottom-up effect was not the main controlling factor for the plankton distribution in this transect. Under the influence of multifactor changes derived by freshwater - seawater mixing， the main controlling factors on the distribution of meso- and macro-plankton exhibited regional differences related with salinity. The present study for the first time conducted in situ observation of plankton using a continuous particle imaging and classification system （CPICS） in some of the high salinity sites， and obtained in situ photographs of meso- and macro-plankton， which could support the species identification of macro-plankton （such as Noctiluca scientillans， Diphyopsis chamissonis）， and could support the identification of copepods to subclass. The results of in situ observation by CPICS （vertically moving） and laboratory analysis of field samples （obtained via vertical tows） showed a similar tendency on the changes of species numbers. In the future， with the help of long-term in situ observation in the whole water column and intelligent analysis of mega-data， CPICS would provide important real-time data for the species composition and evolution of plankton in the East China Sea.

Key words:Yangtze River estuary;plankton;in situ observation;biodiversity