Microbial communities have important functions during spring phytoplankton blooms, regulating bloom dynamics and processing organic matter. Despite extensive research into such processes, an in‐depth assessment of the fungal component is missing, especially for the smaller size fractions. We investigated the dynamics of unicellular mycoplankton during a spring phytoplankton bloom in the North Sea by 18S rRNA gene tag sequencing and a modified CARD‐FISH protocol. Visualization and enumeration of dominant taxa revealed unique cell count patterns that varied considerably over short time scales. The Rozellomycota sensu lato (s.l.) reached a maximum of 10⁵ cells L⁻¹, being comparable to freshwater counts. The abundance of Dikarya surpassed previous values by two orders of magnitude (10⁵ cells L⁻¹) and the corresponding biomass (maximum of 8.9 mg C m⁻³) was comparable to one reported for filamentous fungi with assigned ecological importance. Our results show that unicellular fungi are an abundant and, based on high cellular ribosome content and fast dynamics, active part of coastal microbial communities. The known ecology of the visualized taxa and the observed dynamics suggest the existence of different ecological niches that link primary and secondary food chains, highlighting the importance of unicellular fungi in food web structures and carbon transfer.

中文翻译：

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春季浮游植物开花期间单细胞海洋真菌的多样性和生物量动态

春季浮游植物水华期间，微生物群落具有重要功能，调节水华动态并处理有机质。尽管对此类过程进行了广泛的研究，但仍缺少对真菌成分的深入评估，尤其是对于较小尺寸的部分。我们通过18S rRNA基因标签测序和改良的CARD-FISH方案调查了北海春季浮游植物开花期间单细胞浮游植物的动力学。显性分类单元的可视化和枚举揭示了独特的细胞计数模式，该模式在短时间范围内变化很大。Rozellomycota sensu lato（sl）最多达到10 ^5个细胞^-1，可与淡水计数相比。Dikarya的丰度比以前的值高两个数量级（10 ^5个细胞L ^-1），相应的生物量（最大8.9 mg C m ^-3）可与报道的丝状真菌（具有指定的生态重要性）相媲美。我们的结果表明，单细胞真菌是丰富的，并且基于高的细胞核糖体含量和快速的动力学，是沿海微生物群落的活跃部分。可视化分类单元的已知生态学和观察到的动力学表明，存在着连接初级和次级食物链的不同生态位，这突出了单细胞真菌在食物网结构和碳转移中的重要性。