东海低氧区及邻近水域浮游植物的季节变化

根据2011年5月、8月、11月在东海低氧区及邻近水域(25°00'—33°30'N,120°00'—127°30'E)进行的多学科综合调查,对东海低氧区及邻近水域浮游植物群落结构特征及季节变化进行了相关研究。经Utermhl方法初步分析共鉴定出浮游植物4门74属248种(含变种、变型,不含未定种),主要由硅藻和甲藻组成,此外还有少量的金藻和蓝藻。春季优势种主要为具齿原甲藻(Prorocentrum dentatum)、柔弱伪菱形藻(Pseudo-nitzschia delicatissim)、骨条藻(Skeletonema sp.)和具槽帕拉藻(Paralia sulcata);夏季主要是中肋骨条藻(Skeletonema costatum)和海链藻(Thalassiosira sp.);秋季主要是具槽帕拉藻、圆筛藻(Coscinodiscus sp.)和柔弱伪菱形藻。调查区浮游植物平均细胞丰度在夏季最高,达到85.002×103个/L,春季次之,秋季最低。在水平方向上,春、夏两季,表层浮游植物细胞丰度在近岸出现高值,由近岸到外海细胞丰度逐渐降低;而在秋季则相反,在调查海域的东北部出现高值,随离岸距离的增加细胞丰度逐渐增加。在垂直方向上,春、夏两季,浮游植物细胞丰度在表层出现最大值,随着深度的增加细胞丰度逐渐降低;而在秋季细胞丰度分布比较均匀,随水深变化不明显。调查区表层浮游植物ShannonWiener多样性指数和Pielou均匀度指数的平面分布基本一致,并且与细胞丰度的分布大致呈镶嵌分布。调查浮游植物群落的演替规律是:从春季的甲藻(具齿原甲藻、微小原甲藻(Prorocentrum minimum)等)为主,硅藻(柔弱伪菱形藻、骨条藻等)为辅;演替至夏季的硅藻(中肋骨条藻、海链藻等)为主,甲藻(主要是梭状角藻(Ceratium fusus)和叉状角藻(Ceratium furca))为辅,到秋季进一步演替为硅藻(具槽帕拉藻、圆筛藻、柔弱伪菱形藻等)为主,铁氏束毛藻(Trichodesmium thiebaultii)为辅。浮游植物物种组成、优势种、细胞丰度及多样性指数均表现出明显的时空变化。低氧区与非低氧区浮游植物群集存在明显差异。

Seasonal changes of the phytoplankton along hypoxia area and adjacent waters in the East China Sea

A multidisciplinary comprehensive survey was carried out in hypoxia area and adjacent waters in the East China Sea (25°00''-33°30''N, 120°00''-127°30''E) from May to November 2011. The phytoplankton community structure and seasonal variation were reported in this paper. Water samples were analyzed by means of Utermöhl method. A total of 248 taxa which belong to 74 genera of 4 phyla were identified (including varieties and forms, don''t include uncertain species). Bacillariophyta and Dinophyta were the dominant phytoplankton groups in the survey area, and there were also found a few species belonging to Chrysophyta and Cyanophyta. Most of phytoplankton taxa found in the survey area was temperate coastal species, at the same time, some warm water species and oceanic species were occasional found. In spring, Dinophyta was the most dominant phytoplankton group and the dominant species were Prorocentrum dentatum, Pseudo-nitzschia delicatissim, Skeletonema sp. and Paralia sulcata. In summer, the most dominant phytoplankton group changed to Bacillariophyta and the dominant species were Skeletonema costatum and Thalassiosira sp.. In autumn, Bacillariophyta was also the most dominant phytoplankton group and the dominant species were Paralia sulcata, Coscinodiscus sp. and Pseudo-nitzschia delicatissim. The phytoplankton cell abundance was decreased in turn from summer (85.002×10³ cells/L), spring (66.937×10³ cells/L) to autumn (5.811×10³ cells/L) in the survey area. Horizontally, the surface distribution of phytoplankton cell abundance in the survey area was relatively high in the inshore area and decreased slightly from inshore area to offshore area in spring and summer. On the contrary, the cell abundance was relatively high in the northeast of the survey area and increased slightly from inshore area to offshore area in autumn. Vertically, the cell abundance of phytoplankton was concentrated in surface water and decreased slightly with depth from surface to bottom in spring and summer, while the vertical distribution of phytoplankton cell abundance wasn''t obvious with depth change in autumn. The surface distribution of Shannon-Wiener diversity index and Pielou evenness index was generally consistent, and the diversity indexes were low in the area with high cell abundance. The maximum of these two kinds of index was all appeared in autumn and decreased in turn from autumn, summer to spring. The succession trend of the phytoplankton dominant species in this survey changed from Dinophyta-Bacillariophyta type in spring, Bacillariophyta-Dinophyta type in summer to Bacillariophyta-Cyanophyta type in autumn. Namely, the phytoplankton dominant species was mainly composed of Dinophyta (Prorocentrum dentatum, Prorocentrum minimum etc.) and coexisted with a small amount of Bacillariophyta (Pseudo-nitzschia delicatissim, Skeletonema sp. etc.) in spring. In summer, it was mainly composed of Bacillariophyta (Skeletonema costatum, Thalassiosira sp. etc.) and coexisted with Dinophyta (mainly included Ceratium fusus and Ceratium furca). In autumn, it was mainly composed of Bacillariophyta (Paralia sulcata, Coscinodiscus sp. and Pseudo-nitzschia delicatissim etc.) and coexisted with Cyanophyta (Only included Trichodesmium thiebaultii). Phytoplankton species composition, dominant species, cell abundance and diversity index had pronounced spatial and temporal variation in hypoxia area and adjacent waters in the East China Sea. Phytoplankton assemblage in hypoxia area and non-hypoxia area showed a significant difference.