Protists are extremely diverse morphologically and physiologically, and they play important ecological roles at multiple trophic levels as primary producers and consumers in nearly all microbial communities. In spite of their fundamental importance in marine ecosystems, protistan diversity and distribution has yet to be comprehensively characterized in much of the world ocean, particularly in the vast expanses below the euphotic zone. We examined protistan community structure and species diversity in the oligotrophic North Pacific Subtropical Gyre. Our primary goal was to better characterize the breadth of metabolically active protistan species throughout the water column spanning 12 depths from 5 m to 770 m (~600 m below the euphotic zone) across three seasons using 18S rRNA gene V4 amplicon sequencing of RNA (cDNA).

Protistan community structure changed markedly across relatively narrow ranges of increasing depths between 75 m-100 m, and again between 175 m-300 m. Changes were driven by depth-specific distributions among major protistan taxa associated with the upper mixed layer, deep chlorophyll maximum and aphotic zone, respectively, in this permanently stratified water column. Diatoms and some heterotrophic protists (MAST, choanoflagellates) were important contributors in the upper mixed layer, while haptophytes and pelagophytes increased in relative abundances in the lower euphotic zone. Radiolaria, ciliates and syndinians (putative parasitic protists within the order Syndiniales) increased in relative abundances below the euphotic zone. Overall, the highest taxonomic richness of amplicon sequence variants (ASVs) was observed in aphotic samples. Additionally, the dominant ASVs within some taxonomic groups that were observed in deep water were different than those observed in the upper water column, implying adaptations to specific depth strata rather than passive transport of surface-dwelling species. In contrast to depth-related changes, seasonal changes in protistan community structure were not significant.

生物体在形态和生理上极为不同，它们在几乎所有微生物群落中作为主要生产者和消费者的多重营养水平上发挥着重要的生态作用。尽管前列腺素的多样性和分布在海洋生态系统中具有根本的重要性，但尚未在世界上许多海洋，特别是在富营养区以下的广大广阔地区中全面地表征其多样性和分布。我们研究了贫营养的北太平洋亚热带环流中的原生动物群落结构和物种多样性。我们的主要目标是使用18S rRNA基因V4扩增子RNA测序技术，在三个季节中更好地表征整个水柱中代谢活跃的protatan物种的广度，跨度从5 m到770 m（在富营养区以下约600 m）的12个深度。 ）。

Protistan群落结构在75 m-100 m之间以及175 m-300 m之间相对较窄的增加深度范围内发生了显着变化。在此永久分层水柱中，分别由与上部混合层，深层叶绿素最大值和无水区相关的主要原生生物类群之间的深度特定分布驱动变化。硅藻和一些异养生物（MAST，鞭毛鞭毛虫）是上层混合层的重要贡献者，而触藻类和聚伞类植物在下富营养区的相对丰度增加。lar虫，纤毛虫和Syndinians（Syndiniales阶内的寄生寄生生物）在富营养区以下的相对丰度增加。总体而言，在无光样品中观察到最高的扩增子序列变体（ASV）分类学丰富度。此外，在深水中观察到的某些分类学组中的优势ASV与在上水柱中观察到的ASV不同，这意味着对特定深度层的适应而不是对表层物种的被动运输。与深度相关的变化相反，Protistan群落结构的季节性变化不显着。