Taxonomy as an indicator of trophic diversity in microbial eukaryotic plankton in an Arctic outflow gateway.

Marine microbial eukaryotes are major contributors to oceanic biodiversity and biogeochemical cycling, in both surface and deep waters yet their functional diversity and distribution remain incompletely understood. The Arctic Ocean, with strong environmental gradients, long-term basin isolation, and pronounced water mass stratification provides a model system to test how environmental filtering and evolutionary history might add to current understanding. We examined microbial eukaryote assemblages in the Arctic from Nares Strait into Baffin Bay, testing the hypothesis that dominant trophic strategies track water mass origin. Using high-throughput sequencing of the V4 region of the 18S rRNA gene across two size fractions (0.22–3 μm and 3–50 μm), we characterized communities associated with distinct Arctic water masses during summer. We then used the data set to ascertain the characteristics of rare taxa that dominated in few of the samples. Assemblages at in the four vertically stacked water masses were dominated by dinoflagellates, and heterotrophic lineages. Mixotrophic and phototrophic lineages were mostly confined to the euphotic zone in the absence of likely advective intrusions or sinking earlier blooms.海洋微生物真核生物（marine microbial eukaryotes）是海洋生物多样性与生物地球化学循环的核心贡献者，广泛分布于表层与深层海水，但当前对其功能多样性与分布格局的认知仍存在不足。北冰洋兼具显著的环境梯度、长期的海盆隔离性与清晰的水团分层结构，为探究环境过滤作用与演化历史如何深化现有认知提供了理想的模式系统。本研究针对内尔斯海峡至巴芬湾海域的北极微生物真核生物群落开展调查，旨在验证“优势营养策略与水团来源相匹配”这一假说。研究针对两个粒径分级（0.22–3 μm与3–50 μm）的样品，对18S核糖体RNA基因（18S rRNA gene）的V4区进行高通量测序，解析了夏季北极不同水团对应的微生物真核生物群落特征。随后利用该数据集明确了仅在少量样本中占优的稀有类群的特征。四个垂直分层水团的群落均以甲藻（dinoflagellates）与异养谱系为优势类群。在未出现明显平流侵入或早期藻华沉降的情况下，混养与光合营养谱系大多局限于真光层内。