长江河口中小型浮游动物数量分布、变动及主要影响因素

Factors controlling abundance and distribution of mesozooplankton and microzooplankton in Yangtze River Estuary

于1999年枯水期（2～3月份）、丰水期（8月份）、2000年枯水期（2～3月份）对长江河口浮游动物采样调查，研究了长江河口浮游动物的数量分布、变动及主要影响因素。结果表明：1999年枯水期浮游动物平均数量仅为79．07ind／m^3，浮游动物在河口内与口外海滨形成两个高丰度区，浮游动物个体数量从口门内向近岸及近外海逐渐递减，优势种数量分布情况决定了该期浮游动物总数量分布。1999年丰水期，浮游动物平均数量高达300．89ind／m^3，浮游动物分布不均匀，数量由河口内向近岸水域与近外海水域递增。2000年枯水期，浮游动物数量分布总体趋势与1999年枯水期相同。1999年枯水期、丰水期，2000年3月枯水期，桡足类数量占浮游动物总数量分别为95．54％、85．82％、84．83％，桡足类数量在浮游动物总数量中占绝对优势，并在浮游动物数量分布中起关键作用。浮游动物数量分布受潮周期影响显著，优势种在浮游动物数量潮周期分布中起重要作用。由各样站的浮游动物数量与盐度做回归分析，在枯水期均不成线性关系，在丰水期则成线性相关，回归方程为：Y=0．34134＋0．0112x（r=0．9341，n=8）。此外，长江口浮游动物数量季节变化与温度、径流量、海流及食物等关系密切。

Zooplankton samples were collected from three oceanographic cruises during February-March, 1999 （dry periods）, August 1999 （flood periods） and February-March 2000 （dry periods）, respectively, to investigate the abundance and distribution of zooplankton in Yangtze River estuary due to season variations and other main factors. The results showed that the average abundance of zooplankton was as low as 79.07 ind/m3 during the dry periods in 1999. Two high abundance areas were found inside and outside of the estuary with a gradient of gradually decrease from the estuary to the ocean. The distribution of dominant species during that time period was determined. In contrast, the average abundance of zooplankton during the flood periods in 1999 was as high as 300.89 ind/m3 and gradually increased from estuary towards open ocean. A patch distribution pattern was observed. A similar dry periods distribution pattern was repeated during the dry periods in 2000. Copepoda accounted for 95.54% , 85.82% and 84.83% of total zooplankton during the February- March, 1999, August 1999 and Febuary-March 2000 samplings, respectively. In this study, we found that, Copepoda was the predominant species and played a key role in controlling the abundance and distribution of zooplankton and distribution of dominant species was considerably influenced by the tidal stage. The regression analysis showed no linear correlation between zooplankton abundance and salinity during the dry periods. However, there exists significant linear correlation during the flood periods （ r = 0. 9341, n = 8 ）. In addition, the seasonal variation of zooplankton abundance is closely associated with temperature, river discharge, ocean currents and food.