Marine microbial communities undergo drastic changes during the seasonal cycle in high latitude seas. Despite the dominance of microbial biomass in the oceans, comprehensive studies on the seasonal changes of microbial plankton during the complete winter period are lacking. To study the seasonal variation in abundance of the microbial community, water samples were collected weekly in the Northern Baltic Sea from October to May. During ice cover from mid-January to April, samples from the sea ice and the underlying water were taken in addition to the water column samples. Abundances of bacteria, virus-like particles, nanoflagellates, and chlorophyll a concentrations were measured from sea ice, under-ice water, and the water column, and examined in relation to environmental conditions. All studied organisms had clear seasonal changes in abundance, and the sea-ice microbial community had an independent wintertime development compared to the water column. Bacteria were observed to have a key role in the biotic interactions in both ice and the water column, and the dormant period during the cold-water months (October–May) was limited to before ice formation. Our results provide the first insights into the temporal dynamics of bacteria and viruses during the whole cold-water season (October–May) in coastal high latitude seas, and demonstrate that changes in the environmental conditions are likely to affect bacterial dynamics and have implications on trophic interactions.

中文翻译：

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波罗的海北部秋季至春季微生物群落：冷水季节细菌、病毒和纳米鞭毛虫丰度的时间变化

海洋微生物群落在高纬度海域的季节性周期中发生剧烈变化。尽管海洋中微生物量占主导地位，但缺乏对整个冬季期间浮游微生物季节性变化的综合研究。为了研究微生物群落丰度的季节性变化，从 10 月到 5 月，每周在波罗的海北部收集水样。在 1 月中旬至 4 月的冰盖期间，除了水柱样品外，还采集了海冰和下伏水的样品。从海冰、冰下水和水柱中测量了大量细菌、病毒样颗粒、纳米鞭毛虫和叶绿素 a 浓度，并根据环境条件进行了检查。所有研究的生物体丰度都有明显的季节性变化，与水柱相比，海冰微生物群落具有独立的冬季发展。观察到细菌在冰和水柱中的生物相互作用中起着关键作用，冷水月份（10 月至 5 月）的休眠期仅限于冰形成之前。我们的研究结果首次揭示了沿海高纬度海域整个冷水季节（10 月至 5 月）细菌和病毒的时间动态，并表明环境条件的变化可能会影响细菌动态，并对营养相互作用。冷水月份（10 月至 5 月）的休眠期仅限于结冰之前。我们的研究结果首次揭示了沿海高纬度海域整个冷水季节（10 月至 5 月）细菌和病毒的时间动态，并表明环境条件的变化可能会影响细菌动态，并对营养相互作用。冷水月份（10 月至 5 月）的休眠期仅限于结冰之前。我们的研究结果首次揭示了沿海高纬度海域整个冷水季节（10 月至 5 月）细菌和病毒的时间动态，并表明环境条件的变化可能会影响细菌动态，并对营养相互作用。