While traditional microplankton community assessments focus primarily on phytoplankton and protozooplankton, the last decade has witnessed a growing recognition of photo-phago mixotrophy (performed by mixoplankton) as an important nutritional route among plankton. However, the trophic classification of plankton and subsequent analysis of the trophic composition of plankton communities is often subjected to the historical dichotomy. We circumvented this historical dichotomy by employing a 24 year-long time series on abiotic and protist data to explore the trophic composition of protist communities in the Southern North Sea. In total, we studied three different classifications. Classification A employed our current knowledge by labeling only taxa documented to be mixoplankton as such. In a first trophic proposal (classification B), documented mixoplankton and all phototrophic taxa (except for diatoms, cyanobacteria, and colonial Phaeocystis) were classified as mixoplankton. In a second trophic proposal (classification C), documented mixoplankton as well as motile, phototrophic taxa associated in a principle component analysis with documented mixoplankton were classified as mixoplankton. In all three classifications, mixoplankton occurred most in the inorganic nutrient-depleted, seasonally stratified environments. While classification A was still subjected to the traditional dichotomy and underestimated the amount of mixoplankton, our results indicate that classification B overestimated the amount of mixoplankton. Classification C combined knowledge gained from the other two classifications and resulted in a plausible trophic composition of the protist community. Using results of classification C, our study provides a list of potential unrecognized mixoplankton in the Southern North Sea. Furthermore, our study suggests that low turbidity and the maturity of an ecosystem, quantified using a newly proposed index of ecosystem maturity (ratio of organic to total nitrogen), provide an indication on the relevance of mixoplankton in marine protist communities.

中文翻译：

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探索营养谱：将混合浮游生物置于北海南部的海洋原生生物群落中

虽然传统的微型浮游生物群落评估主要侧重于浮游植物和原生浮游动物，但在过去十年中，人们越来越认识到光吞噬混合营养（由混合浮游生物进行）是浮游生物的重要营养途径。然而，浮游生物的营养分类和随后对浮游生物群落营养组成的分析往往受到历史二分法的影响。我们通过使用非生物和原生生物数据的 24 年时间序列来探索北海南部原生生物群落的营养组成，从而规避了这种历史二分法。我们总共研究了三种不同的分类。分类 A 通过仅标记记录为混合浮游生物的分类群来利用我们目前的知识。在第一个营养提案（B 类）中，记录的混合浮游生物和所有光养类群（硅藻、蓝藻和群落褐藻除外）都被归类为混合浮游生物。在第二个营养提议（C 类）中，记录的混合浮游生物以及与记录的混合浮游生物的主成分分析相关的活动的、光养的分类群被归类为混合浮游生物。在所有三个分类中，混合浮游生物最常出现在无机营养耗尽、季节性分层的环境中。虽然分类 A 仍然遵循传统的二分法并低估了混合浮游生物的数量，但我们的结果表明分类 B 高估了混合浮游生物的数量。分类 C 结合了从其他两个分类中获得的知识，并得出了原生生物群落的合理营养组成。使用分类 C 的结果，我们的研究提供了北海南部潜在的未被识别的混合浮游生物列表。此外，我们的研究表明，使用新提出的生态系统成熟度指数（有机氮与总氮的比率）量化的低浊度和生态系统的成熟度，为混合浮游生物与海洋原生生物群落的相关性提供了指示。