长江口及邻近海域浮游动物群落结构及季节变化

根据2006—2007年长江口及其邻近海域(29°30'N—32°30'N,120°00'E—127°30'E)150个站位4个季节的调查资料,对长江口海域浮游动物群落结构、种类组成、优势种及其季节变化进行研究。结果表明,长江口及其邻近海域浮游动物群落物种多样性丰富,四季共鉴定浮游动物460种,隶属7个门,246属,此外,另有54类浮游幼体。其中,桡足类是最优势类群,有193种,占41.96%;端足类为第二优势类群,有51种,占11.09%;水螅水母为第三优势类群,有34种,占7.39%。长江口及其邻近海域浮游动物的物种多样性呈现明显季节变化,其特征为:夏季(317种)秋季(309种)春季(230种)冬季(138种)。中华哲水蚤和百陶带箭虫为长江口及其邻近海域的四季优势种。长江口及其邻近海域浮游动物大体可划分为5种生态类群:近岸低盐类群、广温广盐类群、低温高盐类群、高温广盐类群和高温高盐类群。结合同步调查的水文和水化学数据,进行浮游动物群落丰度与环境因子的相关分析表明:盐度是影响长江口及其邻近海域的浮游动物群落丰度的主要环境因子。

Seasonal variation in zooplankton community structure in the Changjiang Estuary and its adjacent waters

Seasonal variation of zooplankton community structure, species composition, and dominant species were determined based on samples collected from 150 stations during four research cruises in the Changjiang Estuary and its adjacent waters (29°30''N-32°30''N,120°00''E-127°30''E). The study was conducted from July to August 2006 (Summer), December 2006 to February 2007 (Winter), April to May 2007 (Spring), and October to December 2007 (Autumn). The mesoscale study areas were positioned from the Changjiang Estuary to the transition area where freshwater from the Changjiang plume and offshore water masses, such as the Kuroshio and its branches, mix with each other. In total, 460 species of zooplankton belonging to 246 genera and 18 groups from seven phyla, together with 54 types of pelagic larvae, were identified in the Changjiang Estuary and its adjacent waters during four seasons. The 18 groups of zooplankton included Hydromedusae, Siphonophora, Scyphomedusae, Ctenophora, Polychaeta, Cladocera, Copepoda, Ostracoda, Isopoda, Mysida, Cumacea, Amphipoda, Euphausiacea, Decapoda, Chaetognatha, Appendicularia, Thaliacea, and pelagic Mollusca. The most dominant group of zooplankton was Copepoda, including 193 species and accounting for 41.96% of the total species. Amphipoda ranked second, with 51 species accounting for 11.09% of the total species. Hydromedusa was the third dominant group of zooplankton with 34 species and accounted for 7.39% of the total species. There was considerable seasonal and spatial variation in the community structure of zooplankton in the Changjiang Estuary and its adjacent waters. More zooplankton species were found in summer (317 species and 43 types of pelagic larvae) and autumn (309 species and 28 types of pelagic larvae) than in spring (230 species and 27 types of pelagic larvae) and winter (138 species and 21 types of pelagic larvae). The number of species increased gradually from the inshore to offshore waters and from north to south, during all seasons. There were seasonal changes in dominant species in the Changjiang Estuary and its adjacent waters:in spring and winter, Calanus sinicus was the most dominant species, but in summer and autumn, the most dominant species was replaced by Centropages dorsispinatus and Subeucalanus subcrassus, respectively. Only Calanus sinicus and Zonosagitta bedoti were dominant in all four seasons. Based on species composition and ecological distribution, the zooplankton community in the Changjiang Estuary and its adjacent waters could be divided into five ecological groups, including the coastal brackish water, eurythermal euryhaline, hypothermal hypersaline, hyperthermal euryhaline, and hyperthermal hypersaline group. The dominant species were distributed primarily in the coastal brackish water group and eurythermal euryhaline group. Furthermore, we measured environmental factors and determined the responses of the zooplankton community to the factors, including temperature, salinity, concentration of suspended matter, and concentration of chlorophyll a. Results of Pearson''s correlation analysis revealed that the most important environmental factor influencing changes in zooplankton community structure in the Changjiang Estuary and its adjacent waters was salinity. Furthermore, the Changjiang diluted water introduced a large number of nutrients, which was beneficial to the growth of plankton, but the estuarine turbidity limited the distribution of zooplankton.