The Southern Ocean is facing rapid environmental changes. However, few studies have been conducted on the spatiotemporal variability of mesozooplankton communities under recent climatic conditions, particularly in the eastern Indian sector. This study describes the spatiotemporal variability of the mesozooplankton community and the demographics of large copepods and krill in this sector, sampled through a Rectangular Mid-Water Trawl with 1 m2 mouth area (RMT1) during the austral summer of 2018/2019 as part of the KY1804 survey. Cluster analysis indicated that the mesozooplankton community was divided into five groups that showed only small longitudinal differences, as they were affected by oceanic fronts. Part of the variability was explained by physical (local upwelling) and biological features (e.g., the occurrence of species showing a specific spatial distribution, such as Euphausia crystallorophias). Horizontal changes in the zooplankton community structure were not attributed to temporal changes during the 2-month sampling period. The demographics of the dominant species, Calanoides acutus, Calanus propinquus, Metridia gerlacheri, and Thysanoessa macrura, exhibited significant temporal differences in abundance or mean stage index (MSI) between the early and late seasons. These differences matched the growth rates estimated in previous studies, suggesting that their growth during the study period was constant without regional differences. There were no evident changes in the abundance or demographics of Rhinalanus gigas, suggesting that they were in their reproductive season. These species-specific demographics could be explained by the species life cycles: growth in C. acutus and C. propinquus and reproduction in R. gigas during the austral summer. Abundances and MSIs confirmed the growth of dominant copepods and krill during the sampling period; however, no evident seasonal changes were observed in the zooplankton community structure. The findings of this study contribute to the understanding of lower trophic levels in marine ecosystems and the present carbon cycle in the eastern Indian sector of the Southern Ocean.

中文翻译：

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2018/2019 年南大洋东印度海域中浮游动物群落和人口的时空变化


南大洋正面临快速的环境变化。然而，在最近的气候条件下，特别是在印度东部地区，对中浮游动物群落的时空变化的研究很少。本研究描述了中浮游动物群落的时空变化以及该区域大型桡足类和磷虾的种群统计数据，作为 KY1804 调查的一部分，在 2018/2019 年南方夏季通过具有 1 m2 口面积 （RMT1） 的矩形中层拖网进行采样。聚类分析表明，中浮游动物群落分为 5 组，由于受到海洋锋面的影响，仅表现出很小的纵向差异。部分可变性是由物理（局部上升流）和生物特征（例如，出现显示特定空间分布的物种，例如 Euphausia crystallorophias）来解释的。在 2 个月的采样期间，浮游动物群落结构的水平变化并未归因于时间变化。优势物种 Calanoides acutus、Calanus propinquus、Metridia gerlacheri 和 Thysanoessa macrura 的种群特征在早季和晚季之间表现出显著的丰度或平均阶段指数 （MSI） 的时间差异。这些差异与先前研究中估计的增长率相匹配，表明它们在研究期间的增长是恒定的，没有地区差异。Rhinalanus gigas 的数量或人口统计数据没有明显变化，表明它们正处于繁殖季节。这些物种特异性的人口统计数据可以用物种生命周期来解释：C. acutus 和 C. propinquus 的生长以及 R. gigas 在南方夏季的繁殖。 丰度和 MSI 证实了采样期间优势桡足类和磷虾的生长;然而，在浮游动物群落结构中没有观察到明显的季节性变化。这项研究的结果有助于了解海洋生态系统中较低的营养级和南大洋东印度地区目前的碳循环。