Diatoms are important components of the marine food web and one of the most species-rich groups of phytoplankton. The diversity and composition of diatoms in eutrophic nearshore habitats have been well documented due to the outsized influence of diatoms on coastal ecosystem functioning. In contrast, patterns of both diatom diversity and community composition in offshore oligotrophic regions where diatom biomass is low have been poorly resolved. To compare the diatom diversity and community composition in oligotrophic and eutrophic waters, diatom communities were sampled along a 1,250 km transect from the oligotrophic Sargasso Sea to the coastal waters of the northeast US shelf. Diatom community composition was determined by amplifying and sequencing the 18S rDNA V4 region. Of the 301 amplicon sequence variants (ASVs) identified along the transect, the majority (70%) were sampled exclusively from oligotrophic waters of the Gulf Stream and Sargasso Sea and included the genera Bacteriastrum, Haslea, Hemiaulus, Pseudo-nitzschia, and Nitzschia. Diatom ASV richness did not vary along the transect, indicating that the oligotrophic Sargasso Sea and Gulf Stream are occupied by a diverse diatom community. Although ASV richness was similar between oligotrophic and coastal waters, diatom community composition in these regions differed significantly and was correlated with temperature and phosphate, two environmental variables known to influence diatom metabolism and geographic distribution. In sum, oligotrophic waters of the western North Atlantic harbor diverse diatom assemblages that are distinct from coastal regions, and these open ocean diatoms warrant additional study, as they may play critical roles in oligotrophic ecosystems.

中文翻译：

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西北大西洋的贫营养水域支持着与沿海水域不同的分类多样化的硅藻群落

硅藻是海洋食物网的重要组成部分，也是物种最丰富的浮游植物群之一。由于硅藻对沿海生态系统功能的巨大影响，富营养化近岸生境中硅藻的多样性和组成已得到充分记录。相比之下，硅藻生物量较低的近海寡营养区域的硅藻多样性和群落组成模式尚未得到很好的解决。为了比较贫营养和富营养水域中的硅藻多样性和群落组成，我们沿着从贫营养马尾藻海到美国东北部陆架沿海水域的 1,250 公里横断面对硅藻群落进行了采样。通过对 18S rDNA V4 区域进行扩增和测序来确定硅藻群落组成。在沿横断面鉴定的 301 个扩增子序列变体 (ASV) 中，大多数 (70%) 仅从墨西哥湾流和马尾藻海的贫营养水域取样，包括细菌星藻属、哈氏藻属、半菱形藻属、拟菱形藻属和菱形藻属。硅藻 ASV 丰富度沿横断面没有变化，表明寡营养的马尾藻海和墨西哥湾流被多样化的硅藻群落占据。尽管寡营养水域和沿海水域的 ASV 丰富度相似，但这些地区的硅藻群落组成存在显着差异，并且与温度和磷酸盐这两个已知影响硅藻代谢和地理分布的环境变量相关。总之，北大西洋西部的寡营养水域蕴藏着与沿海地区不同的多种硅藻组合，这些公海硅藻值得进一步研究，因为它们可能在寡营养生态系统中发挥关键作用。