Data from: Vertical gradients in species richness and community composition across the twilight zone in the North Pacific Subtropical Gyre

Although metazoan animals in the mesopelagic zone play critical roles in deep pelagic food webs and in the attenuation of carbon in midwaters, the diversity of these assemblages is not fully known. A metabarcoding survey of mesozooplankton diversity across the epipelagic, mesopelagic and upper bathypelagic zones (0-1500m) in the North Pacific Subtropical Gyre revealed far higher estimates of species richness than expected given prior morphology-based studies in the region (4,024 OTUs, 10-fold increase), despite conservative bioinformatic processing. OTU richness of the full assemblage peaked at lower epipelagic-upper mesopelagic depths (100-300m), with slight shoaling of maximal richness at night due to diel vertical migration, in contrast to expectations of a deep mesopelagic diversity maximum as reported for several plankton groups in early systematic and zoogeographic studies. Four distinct depth-stratified species assemblages were identified, with faunal transitions occurring at 100m, 300m, and 500m. Highest diversity occurred in the smallest zooplankton size fractions (0.2-0.5mm), which had significantly lower % OTUs classified due to poor representation in reference databases, suggesting a deep reservoir of poorly understood diversity in the smallest metazoan animals. A diverse meroplankton assemblage also was detected (350 OTUs), including larvae of both shallow and deep living benthic species. Our results provide some of the first insights into the hidden diversity present in zooplankton assemblages in midwaters, and a molecular reappraisal of vertical gradients in species richness, depth distributions, and community composition for the full zooplankton assemblage across the epipelagic, mesopelagic and upper bathypelagic zones.尽管中层带（mesopelagic zone）的后生动物在远洋深层食物网以及中层水域碳衰减过程中发挥着关键作用，但学界对这类群落的多样性仍未完全探明。本研究针对北太平洋副热带环流内上层带、中层带及上深海带（0~1500m）的中型浮游动物（mesozooplankton）多样性开展元条形码（metabarcoding）调查，尽管采用了保守的生物信息学分析流程，但得到的物种丰富度估计值远高于该区域此前基于形态学研究的预期，共鉴定出4024个操作分类单元（Operational Taxonomic Unit，OTU），增幅达10倍。整个群落的OTU丰富度在浅上层带至中上层带（100~300m）深度达到峰值；受昼夜垂直迁移影响，夜间的丰富度峰值会略微向浅水区偏移，这与早期分类学及动物地理学研究中多个浮游类群多样性峰值出现在深层中层带的预期相悖。研究共识别出4个具有显著深度分层特征的物种种群，群落结构更替的临界深度分别为100m、300m及500m。多样性最高的类群出现在最小粒径分级的浮游动物样本（0.2~0.5mm）中，但由于参考数据库对该类群的覆盖度不足，该分级中被成功注释的OTU占比显著偏低，这表明小型后生动物中存在大量尚未被充分认知的多样性储备。本研究同时检测到多样性丰富的暂时性浮游生物（meroplankton）群落，共包含350个OTU，涵盖浅海及深海底栖物种的幼体。本研究结果为探明中层水域浮游动物群落中的隐蔽多样性提供了首批科学认知，同时对横跨上层带、中层带及上深海带的完整浮游动物群落的物种丰富度垂直梯度、深度分布及群落组成开展了分子水平的重新评估。