Inorganic nutrient limitation affects the stoichiometry and nutritional quality of marine phytoplankton. Mixoplankton, able to photosynthesize and feed simultaneously in the one cell, can compensate shortage of nutrients by phagotrophy, theoretically upgrading their nutritional quality for their predators: the zooplankton. Yet, the additional value that phagotrophy in mixoplankton may provide to support zooplankton growth and recruitment has been poorly explored. Therefore, we investigated the feeding and reproductive performances of the copepods Paracartia grani and Centropages typicus on mono-diets of the dinoflagellate Karlodinium veneficum grown as strict autotroph and as mixotroph, both under N and P depletion, and in nutrient-balanced conditions (f/2 medium; only as autotroph). Feeding and reproduction outputs were generally higher in P. grani than in C. typicus. Both copepod species ingested the mixotrophic K. veneficum at similar rates than the autotrophic ones in either nutrient-limited scenario. However, egg production and recruitment rates generally increased when feeding on mixotrophs, in P. grani on both N- and P-limited diets, and in C. typicus under P limitation. In general, P limitation influenced copepod physiology more than N depletion. Our results show that phagotrophy upgrades nutritional quality in nutrient-limited mixotrophs as prey for copepods compared to the strict autotrophic ones. These findings are among the first reported cases of copepod ingestion in the laboratory on actively feeding mixoplankton, and they highlight the importance of considering the trophic mode of the protist and the response by various zooplanktonic predators when attempting to understand the functioning of marine planktonic food webs.

中文翻译：

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Mixotrophy 提高了海洋类角足类动物的食物质量

无机养分限制影响海洋浮游植物的化学计量和营养品质。混合浮游生物能够在一个细胞中同时进行光合作用和进食，可以通过吞噬来弥补营养不足，理论上可以提高它们捕食者浮游动物的营养质量。然而，混合浮游生物的吞噬作用可能为支持浮游动物生长和补充提供的额外价值尚未得到很好的探索。因此，我们研究了桡足类Paracartia grani和Centropages typicus对甲藻Karlodinium v​​eneficum 的单一饮食的摄食和繁殖性能。在 N 和 P 消耗以及营养平衡条件下（f/2 培养基；仅作为自养）生长为严格的自养和混合养。喂食和再现输出在通常更高P.格拉尼比C. typicus。在两种营养有限的情况下，两种桡足类物种以与自养物种相似的速率摄取混合营养K. veneficum。然而，当以混合营养物为食时，在限制氮和磷的饮食中的P. grani以及C. typicus 中，产蛋率和补充率通常会增加在 P 限制下。一般来说，磷限制比 N 消耗对桡足类生理的影响更大。我们的结果表明，与严格的自养生物相比，吞噬作用提高了营养有限的混合营养生物作为桡足类猎物的营养质量。这些发现是实验室首次报道的关于主动喂养混合浮游生物的桡足类摄入案例之一，它们强调了在试图了解海洋浮游食物网的功能时考虑原生生物的营养模式和各种浮游动物捕食者的反应的重要性.