南海三沙永乐龙洞及邻近海域浮游植物群落结构

Phytoplankton Community Structure in Sansha Yongle Blue Hole and Its Adjacent Area of the South China Sea

南海“三沙永乐龙洞”是目前全球已知最深的海洋蓝洞,具有独特的结构和科学研究价值。根据2017年5月中旬—2017年6月上旬对永乐龙洞及其邻近海域的综合科学考察数据和资料,对龙洞内外浮游植物群落结构进行了比较研究。研究海域水采和网采浮游植物样品共鉴定出浮游植物166种,生态类型以广温广布型类群和热带暖水性类群为主,物种数和细胞丰度以硅藻(10^3种)和甲藻(57种)占主导,其它包括金藻(2种)、绿藻(2种)和蓝藻(2种)。永乐龙洞内浮游植物有63种,细胞丰度平均值为3.02×10^3个·L^-1,主要优势种为菱形藻(Nitzschia spp.)、新月柱鞘藻(Cylindrotheca closterium)和舟形藻(Navicula sp.)等,种类多样性指数和均匀度平均值分别为2.02和0.76;洞外深海区浮游植物有130种,细胞丰度平均值为1.89×10^3个·L^-1,主要优势种为菱形藻(Nitzschia spp.)、角毛藻(Chaetoceros spp.)、菱形海线藻(Thalassionema nitzschioides)和伏氏海线藻(Thalassionema frauenfeldii)等,种类多样性指数和均匀度平均值分别为3.13和0.87。浮游植物主要分布于光照条件较好的上层水体,细胞丰度高值对应于叶绿素a次表层最大值所在水层。Jaccard相似性指数表明永乐龙洞内与洞外深海区浮游植物种类组成有差异,主要体现在永乐龙洞内浮游植物物种数和多样性指数显著低于洞外深海区的。洞内外海水的有限连通性可能是永乐龙洞内外浮游植物群落差异的重要原因。

Sansha Yongle Blue Hole is recognized as the deepest marine blue hole in the world and possesses unique structure and important scientific research values.Based on the comprehensive scientific research carried out during middle May to early June 2017,the phytoplankton community structures in the Yongle Blue Hole and its adjacent area were studied.A total of 166 phytoplankton species were identified in the study area,including 10^3 species of diatoms,57 species of dinoflagellates,and 2 species of chrosophytes,chlorophytes and cyanophytes,respectively.The major ecological types of the phytoplankton were cosmopolitan species and tropical warm water species.Diatoms and dinoflagellates were dominated both in species number and cell abundance.Inside the Yongle Blue Hole,63 species of phytoplankton were identified which were dominated by Nitzschia spp.,Cylindrotheca closterium,and Navicula sp.,ect.The averaged cell abundance was 3.02×10^3 cells·L^-1,and the mean Shannon-Wiever index and Pielou evenness index were 2.02 and 0.76 respectively.In the deep sea area outside of the blue hole,130 species of phytoplankton were identified which were dominated by Nitzschia spp.,Chaetoceros spp.,Thalassionema nitzschioides and Thalassionema frauenfeldii,ect.The averaged cell abundance was 1.89×10^3 cells·L^-1,and the mean Shannon-Wiever index and Pielou evenness index were 3.13 and 0.87 respectively.The phytoplankton distributed mainly in the light illuminated upper water column and the higher cell abundance layer was corresponding to the subsurface chlorophyll maximum.The Jaccard similarity coefficient suggested a significant differences of species composition were among the study areas,which were mainly reflected by the lower species number and diversity index inside the blue hole than that in the deep sea area outside the blue hole.The limited seawater connectivity and exchange might be the important reason for the difference of phytoplankton community structure between the inside and the outside of the Yongle Blue Hole.