Phyto- and zooplankton in Arctic and sub-Arctic seas show very strong seasonal changes in diversity and biomass. Here we document the seasonal variability in the mesozooplankton community structure in a sub-Arctic fjord in Northern Norway based on monthly sampling between November 2018 and February 2020. We combined traditional morphological zooplankton identification with DNA metabarcoding of a 313 base pair fragment of the COI gene (Leray-XT). This approach allowed us to provide the most detailed mesozooplankton species list known for this region across an entire year, including both holo- and meroplankton. The zooplankton community was dominated by small copepods throughout the sampling period both in terms of abundance and relative sequence counts. However, meroplankton was the most diverse group, especially within the phylum polychaeta. We identified three distinct periods based on the seasonal analysis of the zooplankton community composition. The pre-spring bloom period (February-March) was characterized by low abundance and biomass of zooplankton. The spring-summer period (April-August) was characterized by a succession of meroplankton and a relatively high abundance of copepods of the genus Calanus spp.. Finally, the autumn-winter period (September-December) was characterized high copepod diversity and a peak in abundance of small copepods (e.g Oithona similis, Acartia longiremis, Pseudocalanus acuspes, Pseudocalanus elongatus, Pseudocalanus moultoni, Pseudocalanus minutus. During this period, we also observed an influx of boreal warm-water species which were notably absent during the rest of the year. Both the traditional community analysis and metabarcoding were highly complementary and with a few exceptions showed similar trends in the seasonal changes of the zooplankton community structure.

中文翻译：

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形态学和分子学方法揭示的亚北极峡湾浮游动物群落结构的季节性变化

北极和亚北极海域的植物和浮游动物在多样性和生物量方面表现出非常强烈的季节性变化。在这里，我们根据 2018 年 11 月至 2020 年 2 月期间的每月采样记录了挪威北部亚北极峡湾中浮游动物群落结构的季节性变化。我们将传统形态学浮游动物鉴定与 COI 基因的 313 碱基对片段的 DNA 元条形码相结合(莱雷-XT)。这种方法使我们能够提供该地区全年已知的最详细的中型浮游动物物种清单，包括全浮游生物和小型浮游生物。在整个采样期间，在丰度和相对序列计数方面，浮游动物群落以小型桡足类为主。然而，浮游生物是最多样化的群体，尤其是在多毛门中。我们根据浮游动物群落组成的季节性分析确定了三个不同的时期。春季前盛开期（2 月至 3 月）的特点是浮游动物丰度和生物量低。春夏时期（4-8 月）的特点是浮游生物的演替和Calanus spp. 属桡足类的丰度相对较高。最后，秋冬时期（9-12 月）的特点是桡足类多样性高，小型桡足类动物（例如 Oithona similis、Acartia longiremis、Pseudocalanus acuspes、Pseudocalanus elongatus、Pseudocalanus moultoni、Pseudocalanus minutus 的丰度达到顶峰。在此期间，我们还观察到大量北方温水物种的涌入，这些物种在其余时间明显不存在年。