California Current Cruise CCE-P1408 Process Cruise #6

Passive sinking of particulate organic matter (POM) is the main mechanism through which the biological pump transports surface primary production to the ocean interior. However, the contribution and variability of different biological sources to vertical export is not fully understood. In this work, we use DNA metabarcoding of 18S rRNA gene and particle interceptor traps (PITs) to characterize the taxonomic composition of particles sinking out of the photic layer in the California Current Ecosystem. The PITs included formalin-fixed and 'live' traps to investigate compositional changes associated with consumption and remineralization processes. Sequences affiliated to Radiolaria, mainly Spumellaria and Acantharia, dominated the eukaryotic assemblage in fixed-traps (90%) with Dinophyta and Metazoa making minor contributions. The prominence of Radiolaria decreased markedly in live-traps (<3%), possibly due to selective consumption by large copepods, heterotrophic nanoflagellates and amoeboid phaeodarians that were heavily enriched in these traps. These patterns were consistent across the coastal-to-open water masses surveyed, despite major differences in productivity and trophic structure of the epipelagic plankton community. Our findings indicate that in addition to more commonly considered phytoplankton and crustacean zooplankton, the role of rhizarians can be significant for POM vertical export and cycling in the CCE and potentially in other oceanic ecosystems.颗粒有机物（Particulate Organic Matter，POM）的被动沉降是生物泵将表层初级生产输送至海洋内部的核心机制。然而，不同生物源对颗粒物垂直输出的贡献程度与变异规律，迄今尚未得到完全阐明。本研究借助18S核糖体RNA基因（18S rRNA gene）的DNA宏条形码技术（DNA metabarcoding）与颗粒捕获器（particle interceptor traps，PITs），对加利福尼亚流生态系统（California Current Ecosystem）中从透光层沉降出的颗粒物的分类组成展开表征分析。本次实验设置的PITs分为福尔马林固定陷阱与活体陷阱两类，旨在探究与颗粒物消耗及再矿化过程相关的群落组成变化。在固定陷阱中，隶属于放射虫门（Radiolaria，主要包含泡沫虫亚目Spumellaria与棘虫亚目Acantharia）的序列在真核生物群落中占据绝对优势，占比高达90%；双鞭毛虫门（Dinophyta）与后生动物门（Metazoa）的贡献占比相对有限。而在活体陷阱中，放射虫门的群落占比显著下降（不足3%），这一现象可能源于该类陷阱中大量富集的大型桡足类（copepods）、异养鞭毛虫（heterotrophic nanoflagellates）及变形虫状放射虫（amoeboid phaeodarians）的选择性捕食作用。尽管所调查的近岸至开阔大洋水团在初级生产力与上层浮游生物群落的营养结构上存在显著差异，但上述群落组成模式在所有水团中均保持一致。本研究结果表明，除学界普遍关注的浮游植物与甲壳类浮游动物外，根足虫类（rhizarians）在加利福尼亚流生态系统（CCE）乃至其他海洋生态系统的POM垂直输出与碳循环过程中，均可发挥重要作用。