Mixotrophic eukaryotes are important bacterivores in oligotrophic open oceans, but their significance as grazers in more nutrient-rich waters is less clear. Here, we investigated the bacterivory partition between mixotrophs and heterotrophs in a productive, estuary-influenced coastal region in the East China Sea. We found ubiquitous, actively feeding phytoplankton populations and taxa with mixotrophic potential by identifying ingestion of fluorescent prey surrogate and analyzing community 18S rRNA gene amplicons. Potential and active mixotrophs accounted for 10–63% of the total eukaryotic community and 17–69% of bacterivores observed, respectively, contributing 6–48% of estimated in situ bacterivory. The much higher mixotroph fitness outside of the turbid plume was potentially driven by increased light and decreased nutrient availability. Our results suggest that, although heterotrophs dominated overall in situ bacterivory, mixotrophs were abundant and important bacterivores in this low-latitude mesotrophic coastal region.

中文翻译：

---

河口海岸环境中食菌兼营养生物的相对重要性

混合营养真核生物是寡营养开放海洋中重要的食菌生物，但它们在营养更丰富的水域中作为食草动物的重要性尚不清楚。在这里，我们研究了东海受河口影响的沿海地区的混合营养生物和异养生物之间的细菌划分。通过识别荧光猎物替代物的摄入并分析群落 18S rRNA 基因扩增子，我们发现了无处不在、活跃的浮游植物种群和具有混合营养潜力的类群。潜在和活跃的混合营养生物分别占真核生物群落总数的 10-63% 和观察到的食菌动物的 17-69%，占估计原位食菌的 6-48%。浑浊羽流之外的混合营养体适应性要高得多，这可能是由于光照增加和养分可用性下降所致。我们的结果表明，尽管异养生物在整体原位食菌中占主导地位，但在这个低纬度中营养沿海地区，混合营养生物是丰富且重要的食菌动物。