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 100...

尽管中层带（mesopelagic zone）的后生动物在深海浮游食物网及中层水域碳衰减过程中发挥着关键作用，但目前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区（North Pacific Subtropical Gyre）上层带（epipelagic zone）、中层带（mesopelagic zone）及上半深海带（upper bathypelagic zone，0~1500m）范围内的中型浮游动物（mesozooplankton）开展元条形码（metabarcoding）测序调查；尽管采用了保守的生物信息学处理流程，所得物种丰富度估计值仍远高于该区域此前基于形态学研究的预期，共获得4024个操作分类单元（Operational Taxonomic Unit，OTU），较此前预估提升10倍。全群落的OTU丰富度峰值出现在上层带下部至中层带上部的深度区间（100~300m），受昼夜垂直迁移（diel vertical migration）影响，夜间的丰富度峰值会略微上移；这与早期分类学和动物地理学研究中，多个浮游类群的多样性峰值出现在中层带深部的预期相悖。本研究共识别出4个明确的深度分层物种群落，群落过渡带发生于100米深度处……