Microbial food web (MFW) in the seawater encompasses the smallest organisms: viruses, autotrophic prokaryotes and heterotrophic prokaryotes (HP), nanoflagellates, eukaryotic phytoplankton and ciliates. For many years, scientists investigated the MFW structure differences in distinct water masses. However, the MFW structure seasonal variation in coastal areas remains poorly documented. In this study, we report on the seasonal and spatial variations of the MFW structure in the temperate Sanggou Bay in four successive seasons, from spring to winter. With a temperature increase from 1.90 to 24.20°C, HP biomass increased from 3.77 to 135.77 μg C dm–3, almost covering the whole variation range for the global ocean. The autotrophic (AUTO) components, including Synechococcus, phototrophic picoeukaryotes (PEUK) and pigmented nanoflagellates (PNF), exhibited biomass variation ranges as large as previously reported. The MFW structure seasonal variation was driven by MFW relative biomasses (biomass ratios of MFW components to HP). With the increase of HP biomass, PNF and PEUK relative biomasses increased more rapidly than those of other groups while that of ciliates slightly decreased. The HETE:AUTO (biomass ratio of heterotroph to autotroph organisms) decreased with temperature, it was <1 in summer and >1 in other seasons. Cluster analyses distinguished Inside Bay and Outside Bay on the basis of hydrological characteristics. Consistently, the two subdivisions of Sanggou Bay exhibited different MFW structures as well as distinct tintinnid communities. The main MFW structure difference between Inside and Outside Bay was the biomass ratios of AUTO components to HP. Our results showed that the variations of autotrophic component biomass ratios relative to HP were the main factor responsible for the MFW structure seasonal variation. The spatial difference in MFW structure as well as in tintinnid taxonomic composition between Inside and Outside Bay was linked to the semienclosed nature of the Bay that does not favor efficient mixing with outside Yellow Sea waters.

中文翻译：

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半封闭温带海湾远洋微生物食物网结构的季节和空间变化

海水中的微生物食物网 (MFW) 包括最小的生物：病毒、自养原核生物和异养原核生物 (HP)、纳米鞭毛虫、真核浮游植物和纤毛虫。多年来，科学家们一直在研究不同水团的 MFW 结构差异。然而，沿海地区的 MFW 结构季节性变化仍然缺乏记录。在这项研究中，我们报告了温带桑沟湾从春季到冬季连续四个季节的 MFW 结构的季节和空间变化。随着温度从 1.90°C 增加到 24.20°C，HP 生物量从 3.77 增加到 135.77 μg C dm-3，几乎涵盖了全球海洋的整个变化范围。自养 (AUTO) 组分，包括聚球藻、光养微核生物 (PEUK) 和色素纳米鞭毛虫 (PNF)，表现出的生物量变化范围与先前报道的一样大。MFW 结构季节性变化由 MFW 相对生物量（MFW 组分与 HP 的生物量比）驱动。随着HP生物量的增加，PNF和PEUK的相对生物量比其他组增加得更快，而纤毛虫的相对生物量略有下降。HETE:AUTO（异养生物与自养生物的生物量比）随温度降低，夏季<1，其他季节>1。聚类分析根据水文特征区分了内湾和外湾。一致地，桑沟湾的两个分区表现出不同的MFW结构以及不同的tintinnid群落。内部和外部海湾之间的主要 MFW 结构差异是 AUTO 组件与 HP 的生物量比率。我们的结果表明，自养组分生物量比相对于 HP 的变化是造成 MFW 结构季节性变化的主要因素。内湾和外湾之间 MFW 结构的空间差异以及 tintinnid 分类学组成与海湾的半封闭性质有关，该性质不利于与黄海水外的有效混合。