Summer upwelling off Hainan Island (northern South China Sea) is influenced by fresher coastal water masses. To assess the ecological effects of this complicated oceanography, a cruise was conducted in August 2016. We investigated the spatial patterns of phytoplankton size structure, diversity and quantity of small eukaryotes (0.2–20 μm) across the upwelling system. In the inner-shelf waters, nanophytoplankton contributed a higher proportion to phytoplankton biomass than microphytoplankton and picophytoplankton. High-throughput sequencing of 18S rRNA genes and community analysis indicated that the horizontal variation in community structure of small eukaryotes was larger than the vertical. The relative sequence proportions of dinoflagellates, diatoms, ciliates and Micromonas in the surface layer gradually decreased from the inner shelf to the slope, whereas the Rhizaria, Bathycoccus and Ostreococcus exhibited an opposite trend. The spatial patterns of taxon-specific rDNA copy numbers were similar to the patterns based on the relative proportions. Redundancy analysis revealed that turbidity, salinity and |${\mathrm{NO}}_3^{-}$| were the most important environmental variables in structuring the community of small eukaryotes. The cell abundance of photosynthetic picoeukaryotes was significantly correlated with the rDNA abundance of Mamiellophyceae and the cell abundance of nanoeukaryotes was significantly correlated with the rDNA abundance of dinoflagellates plus diatoms.

中文翻译：

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南海北部沿海上升流区小规模真核浮游生物的大小结构，系统发育多样性，群落组成和丰富度的空间变化

海南岛（南海北部）上流的夏季受到较新的沿海水团的影响。为了评估这一复杂海洋学的生态影响，2016年8月进行了一次航行。我们调查了上升流系统中浮游植物大小结构的空间格局，小型真核生物（0.2–20μm）的多样性和数量。在陆架内部水域，纳米浮游植物对浮游生物生物量的贡献要高于微浮游植物和微浮游植物。18S rRNA基因的高通量测序和群落分析表明，小真核生物群落结构的水平变异大于垂直变异。鞭毛，硅藻，纤毛和微单胞菌的相对序列比例从表层到内陆，表层土壤的含量逐渐下降，而根茎，深层球菌和骨球菌则呈现相反的趋势。分类单元特异性rDNA拷贝数的空间模式类似于基于相对比例的模式。冗余分析显示，浊度，盐度和| $ {\ mathrm {NO}} _ 3 ^ {-} $ | 是构建小型真核生物群落最重要的环境变量。光合微核生物的细胞丰度与毛状藻科的rDNA丰度显着相关，纳米真核生物的细胞丰度与单鞭毛藻和硅藻的rDNA丰度显着相关。