Assessing the link between zooplankton, microbes and the global biogeochemical cycles

甲壳类浮游动物是海洋中最丰富的大型生物之一。它们是海洋营养食物网的重要组成部分，将新合成的有机物质从浮游植物引导到更高的营养水平。然而，它们也与异养微生物相互作用，提供了富含有机物和营养物质、低氧气浓度和低pH的微环境。因此，它们促进特定微生物组的繁殖，促进在海洋中上层生态系统的开放水域中普遍未得到充分代表的代谢过程，如发酵和化生。因此，浮游动物和与浮游动物相关的微生物群在有机质和营养物质的再循环中起着重要的作用。然而，在浮游动物通常栖息的海洋中上层水域，浮游动物及其微生物群介导的生物地球化学过程的速率和通量知之甚少。该提案旨在将通常独立研究的海洋食物网的两个方面--浮游动物生态学和微生物海洋学联系起来。这项拟议的研究将调查浮游动物活动对沿海水域原核生物群落组成和活动的影响。我们建议使用分析化学和微生物学技术相结合的多学科方法来促进我们对浮游动物与生物地球化学循环的主要驱动力原核生物之间的相互作用的理解。因此，这项研究的预期结果也将有助于更好地了解浮游动物及其相关微生物群对全球生物地球化学循环的总体影响。将采集北海南部的主要桡足类群，并确定与桡足类相关的微生物群落的群落组成。将特别关注北海沿海的三个主要桡足类物种，即Acartia tonsa、Pseudocalanus和Calanus helGolandicus。自由生活微生物群落组成和活性对浮游动物捕食浮游植物的响应将在培养实验中进行评估，并与周围水域的微生物群落进行比较。将使用单细胞活性测量、元基因组学和元转录组学来评估浮游动物放牧刺激的微生物群和代谢途径，并与未接触浮游动物放牧副产品的环境水微生物进行比较。此外，培养实验将被用来评估浮游动物放牧在营养物质再循环中的潜在作用，例如，铁和含氧水域中甲烷的释放。

Crustacean zooplankton are one of most abundant macro organisms in the ocean. They are important constituents of the marine trophic food webs, channeling the newly synthesized organic matter from phytoplankton towards higher trophic levels. However, they also interact with heterotrophic microbes, providing microenvironments rich in organic matter and nutrients, low oxygen concentration and pH. Consequently, they facilitate the proliferation of specific microbial groups and promote metabolic processes that are generally underrepresented in open water of marine pelagic ecosystems, such as fermentation and metanogenesis. Therefore, zooplankton and the zooplankton-associated microbiome play an important role in the organic matter and nutrients re-cycling. However, little is known about rates and fluxes of the biogeochemical processes mediated by zooplankton and their microbiome in marine pelagic waters, where zooplankton usually reside. The proposal aims to link two aspects of the marine food web usually independently studied, zooplankton ecology and microbial oceanography. The proposed study will investigate the influence of zooplankton activity on the composition and activity of prokaryotic communities in coastal waters. We propose to use a multidisciplinary approach that combines analytical chemical and microbiological techniques to advance our understanding on the interaction between zooplankton and the main drivers of the biogeochemical cycles, the prokaryotes. Therefore, the expected results from this study should also contribute to better understand the overall impact of zooplankton and their associated microbiome on the global biogeochemical cycles. The dominant copepod groups from the southern North Sea will be collected and the community composition of the copepod-associated microbial community will be determined. Special focus will be devoted in three of the main copepod species from the coastal North Sea, i.e., Acartia tonsa, Pseudocalanus and Calanus helgolandicus. The response of the free living microbial community composition and activity to zooplankton grazing on phytoplankton will be assessed during incubation experiments, and compared to the microbial community from the ambient waters. Single cell activity measurements, metagenomics and metatranscriptomics will be used to assess the microbial groups and metabolic pathways stimulated by zooplankton grazing in comparison to ambient water microbes not exposed to zooplankton grazing by-products. Additionally, the incubation experiments will be used to assess the potential role of zooplankton grazing in nutrient re-cycling, e.g., iron, and methane release in oxygenated waters.