We have profound knowledge on biodiversity on Earth including plants and animals. In the recent decade, we have also increased our understanding on microorganisms in different hosts and the environment. However, biodiversity is not equally well studied among different biodiversity groups and Earth's systems with eukaryotes in freshwater sediments being among the least known. In this study, we used high-throughput sequencing of the 18S rRNA gene to investigate the entire diversity of benthic eukaryotes in three distinct habitats (littoral sediment and hard substrate, profundal sediment) of Lake Ohrid, the oldest European lake. Eukaryotic sequences were dominated by annelid and arthropod animals (54% of all eukaryotic reads) and protists (Ochrophyta and Ciliophora; together 40% of all reads). Eukaryotic diversity was 15% higher in the deep profundal than on either near-surface hard substrates or littoral sediments. The three habitats differed in their taxonomic and functional community composition. Specifically, heterotrophic organisms accounted for 92% of the reads in the profundal, whereas phototrophs accounted for 43% on the littoral hard substrate. The profundal community was the most homogeneous, and its network was the most complex, suggesting its highest stability among the sampled habitats.

中文翻译：

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欧洲最古老湖泊底栖真核生物多样性清单

我们对地球上的生物多样性（包括植物和动物）有着深刻的了解。近十年来，我们也增加了对不同宿主和环境中微生物的了解。然而，不同生物多样性群体和地球系统之间的生物多样性研究并不充分，淡水沉积物中的真核生物是最不为人知的。在这项研究中，我们使用 18S rRNA 基因的高通量测序来研究欧洲最古老湖泊奥赫里德湖三个不同栖息地（沿海沉积物和硬底物、深底沉积物）中底栖真核生物的整体多样性。真核序列主要由环节动物和节肢动物（占所有真核生物的 54%）和原生生物（Ochrophyta 和 Ciliophora；占所有读数的 40%）主导。深海的真核生物多样性比近地表硬质基质或沿海沉积物高 15%。这三个栖息地的分类和功能群落组成不同。具体来说，异养生物占深部读数的 92%，而光养生物占沿海硬质基质上的 43%。深层群落最同质化，其网络最复杂，表明其在采样栖息地中的稳定性最高。