Although parasitism is one of the most prevalent interactions in nature, studies of aquatic food webs rarely include parasites. Syndiniales (Dinophyceae, Alveolata) is a diverse parasitic group of dinoflagellates, common in all marine environments, and are described as dominant components of pelagic ecosystems. However, their temporal dynamics, prevalence, and host-specificity are poorly known. Using DNA metabarcoding to explore trophic interactions of zooplankton, we found a high proportion of Syndiniales sequence reads associated with the targeted consumers. We observed the occurrence of Syndiniales in copepods, cladocerans, appendicularians, and polychaete larvae, ranging between 11 and 36% relative read abundance, encompassing 11 main putative clades. Zooplankton–Syndiniales interactions showed variability in occurrence across the taxa, but also certain host-specificity. The study suggests that the observed copepod–Syndiniales interactions can be both direct parasitic infections and the result of trophic transmission through potentially infected prey by Syndiniales. Given the quantitative importance of Syndiniales and zooplankton in marine environments, our findings emphasize that their interactions should be recognized as key players in the structure and connectivity of plankton food webs.

尽管寄生是自然界中最普遍的相互作用之一，但对水生食物网的研究很少包括寄生虫。Syndiniales（Dinophyceae，Alveolata）是在所有海洋环境中普遍存在的鞭毛藻的寄生群，被描述为远洋生态系统的主要组成部分。然而，他们的时间动态，患病率和宿主特异性是鲜为人知的。使用DNA metabarcoding探索浮游动物的营养相互作用，我们发现与目标消费者相关的Syndiniales序列读段的比例很高。我们观察到co足类，cladocerans，appendicularians和polychaete幼虫中Syndiniales的发生，相对阅读丰度在11％到36％之间，包括11个主要的假定进化枝。浮游动物与Syndiniales的相互作用显示出整个类群发生的变异性，而且还具有特定的主机特异性。研究表明，观察到的pe足类动物与Syndiniales的相互作用既可以是直接的寄生虫感染，也可以是通过Syndiniales通过潜在感染的猎物进行营养传递的结果。鉴于Syndiniales和浮游动物在海洋环境中的定量重要性，我们的研究结果强调，它们之间的相互作用应被视为浮游生物食物网的结构和连通性的关键参与者。