Microzooplankton play an important role in aquatic food webs through their multiple interactions with other organisms and their impact on carbon export. They are major predators of phytoplankton and bacteria while being preyed on by higher trophic levels. Microzooplankton diversity (Dinoflagellates, DIN and Ciliates, CIL), community structure, interaction with phytoplankton and its potential in channeling carbon to higher trophic levels were studied in contrasting productivity regimes (off- and on-plateau, the latter been naturally fertilized by iron) around the Kerguelen islands in the Southern Ocean (SO). DIN and CIL diversity was sampled in late summer (February–March 2018; project MOBYDICK) and at the onset-of the bloom (KEOPS2 cruise), and assessed by Illumina sequencing of 18S rDNA amplicons and microscopic observations. The diversity obtained by the two approaches could be compared at a relatively high taxonomic level (i.e., often to family level). In particular for DIN, relative abundances and ranking of dominant taxa differed between sequencing and microscopy observations. CIL were always recorded at considerably lower abundances than DIN, the median of their abundances across stations and seasons being 350 and 1370 cells L⁻¹, respectively. During late summer, DIN and CIL biomasses were about 1.5 times higher on- than in off-plateau waters, while community composition was spatially similar. The most abundant DIN at all stations and during both seasons were small Gymnodinium (<20 μm). During late summer, ciliates Lohmaniella oviformis (<20 μm) and Cymatocylis antarctica (20-40 μm) dominated on- and off-plateau, respectively. Dilution experiments suggested significant grazing of microzooplankton on phytoplankton as phytoplankton net growth (k) was lower than microzooplankton grazing (g) at all stations (mean k = 0.16 ± 0.05 d⁻¹, g = 0.36 ± 0.09 d⁻¹) in late summer. Despite having great potential as a phytoplankton grazer, microzooplankton occurred at low biomass and showed little temporal variability, suggesting that it was controlled by copepod predation. Microzooplankton is a key component of the SO as an intermediate trophic level mediating carbon transfer from primary producers to higher trophic levels.

微藻浮游生物通过与其他生物的多种相互作用及其对碳出口的影响，在水产食物网中发挥重要作用。它们是浮游植物和细菌的主要捕食者，同时被更高的营养水平所捕食。在不同的生产力状况下（高原和非高原，铁自然地受精），研究了微浮游动物的多样性（恐龙鞭毛虫，DIN和纤毛虫，CIL），群落结构，与浮游植物的相互作用及其将碳引导至更高营养水平的潜力。在南大洋（K）的Kerguelen群岛周围。在夏末（2018年2月至3月； MOBYDICK项目）和盛放期开始（KEOPS2航行）时，对DIN和CIL多样性进行了采样，并通过Illumina对18S rDNA扩增子的测序和显微镜观察进行了评估。可以在相对较高的分类学水平（即经常与家庭水平）比较这两种方法获得的多样性。特别是对于DIN，测序和显微镜观察之间的相对丰度和主要分类单元的等级有所不同。记录的CIL丰度始终比DIN低得多，跨站和季节的丰度中位数分别为350和1370个细胞L^-1。夏季末期，DIN和CIL的生物量在高原上比在离岸水域高约1.5倍，而群落组成在空间上相似。在所有站点以及两个季节中，最丰富的DIN是小型裸子草（<20μm）。夏末期间，纤毛虫卵在大体高原和非高原，分别为卵形的罗氏杆菌（<20μm）和南极纤毛虫（Cymatocylis antarctica）（20-40μm）。稀释实验表明，在所有站上，浮游植物的微浮游植物明显放牧，因为浮游植物的净生长量（k）低于微浮游植物的放牧（g）（平均k = 0.16±0.05 d ^-1，g = 0.36±0.09 d ^-1）在夏末。尽管微浮游植物具有作为浮游植物放牧者的巨大潜力，但它在低生物量时发生，并且几乎没有时间变化，表明它是由co足类捕食所控制的。微浮游生物是SO的关键成分，是介导从初级生产者向更高营养级的碳转移的中间营养级。