Frequent sampling of zooplankton is essential to understand their annual dynamics. However, in polar and subpolar ecosystems, such sampling is rare. This study comparatively analysed, for the first time, the annual mesozooplankton succession in the northwest nearshore and external zones of Ushuaia Bay in the sub-Antarctic Beagle Channel by monthly sampling over two years. The nearshore zone, with shallow waters and strong continental and anthropogenic influence, was characterised by the year-round occurrence of the euryhaline copepod Eurytemoraamericana and adventitious taxa. The mesozooplankton community exhibited pronounced monthly and year-to-year variability but, as a general seasonal trend, winter assemblages were dominated by the copepod Oithona similis and adventitious nematodes, whereas the spring–summer ones were dominated by E. americana, the cladoceran Podon leuckarti and Cirripedia nauplii. In the external zone, the copepods Drepanopus forcipatus and Ctenocalanus citer were found throughout the year. The annual succession showed a clearer seasonal pattern. Main shifts in community structure occurred in late winter–spring and late summer–autumn, when a high representation of meroplankton and appendicularians was closely associated with phytoplankton blooms. The higher temporal variability in the nearshore community was partially related to variable contributions of adventitious taxa to assemblage composition and may be also reflecting stressful conditions for plankton species linked to freshwater and urban discharges reported within the bay. This study allowed filling the temporal gaps in previous research and providing a more complete picture of the annual mesozooplankton dynamics in the Beagle Channel, generating hypotheses at the community and population levels for future research.

中文翻译：

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亚南极湾（南美洲南端比格尔海峡）中浮游动物的演替：两个环境不同区域之间独特的年度模式

频繁采样浮游动物对于了解它们的年度动态至关重要。然而，在极地和亚极地生态系统中，这种采样很少见。本研究首次对亚南极比格尔海峡乌斯怀亚湾西北近岸和外围区域的年度中型浮游动物演替进行了两年多的月采样比较分析。近岸带浅水区，受大陆和人为影响较大，常年出现广盐性桡足类 Eurytemoraamericana 和不定类群。中型浮游动物群落表现出明显的月度和年度变化，但作为一般的季节性趋势，冬季群落以桡足类 Oithona similis 和不定线虫为主，而春夏季群落以 E. americana 为主，枝角类 Podon leuckarti 和 Cirripedia 无节幼体。在外部区域，全年都发现了桡足类 Drepanopus forcipatus 和 Ctenocalanus citer。年度演替显示出更清晰的季节性模式。群落结构的主要变化发生在冬末春末和夏末秋末，此时浮游植物和附肢的高代表与浮游植物大量繁殖密切相关。近岸群落较高的时间变异性部分与不定分类群对组合组成的不同贡献有关，也可能反映了与海湾内报告的淡水和城市排放相关的浮游生物物种的压力条件。