The Ross Sea is a highly productive system characterized by a seasonal succession of phytoplankton groups. However, most of the current understanding is based on observations on the continental shelf in spring and summer at relatively coarse taxonomic resolution. Here, we characterize community composition (class to species) using V4-18S rRNA gene metabarcoding on transects to and across the Ross Sea (shelf-slope and oceanic subregions) during two voyages covering the Austral summer–autumn progression in successive years. Phytoplankton composition shifted from low-diversity diatom-dominated (50%) communities during the summer to more diverse dinoflagellate-dominated (48%) systems during the lower-productivity autumn season. Prymnesiophyceae abundance was low on both voyages (10%), except on the southeast shelf-slope, where Phaeocystis antarctica dominated a shallow mixed layer, contrary to its reported preference for deep-mixing conditions. Amplicon sequence variant analysis identified distinct spatial patterns for two P. antarctica genotypes yet clustered certain species of Bacillariophyta and Prymnesiophyceae, indicating similar environmental preference for genotypes in these groups. Multivariate analysis of environmental drivers found a higher correlation of community composition variation with salinity and macronutrients, but less so with mixed layer depth, considered a primary determinant of taxonomic composition in the Ross Sea. Comparison between years established that community composition was temporally more stable in oceanic relative to shelf-slope waters. This study of seasonal variation of phytoplankton community composition at finer taxonomic resolution provided insights into species- and strain-specific distribution, ecological preferences, and relationships to environmental conditions in the wider Ross Sea to inform modeling and projection of future regional changes.

中文翻译：

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夏秋过渡期间罗斯海地区的环境驱动力和浮游植物多样性

罗斯海是一个高产系统，其特点是浮游植物群的季节性演替。然而，目前的大部分认识都是基于对春季和夏季大陆架的观测，分类分辨率相对粗糙。在这里，我们使用 V4-18S rRNA 基因元条形码对连续几年覆盖澳大利亚夏季-秋季进程的两次航程中往返罗斯海（陆架斜坡和海洋分区）的横断面进行群落组成（类到物种）的描述。浮游植物组成从夏季低多样性硅藻为主的群落（50%）转变为生产力较低的秋季以更多样化的甲藻为主（48%）的系统。除了在东南陆架斜坡上，南极褐囊藻在浅混合层中占主导地位，这与报道的其对深层混合条件的偏好相反，在两次航行中，Prymnesiophyceae丰度都很低（10%） 。扩增子序列变异分析确定了两种南极洲 P. antarctica基因型的不同空间模式，但对硅藻门和 Prymnesiophyceae 的某些物种进行了聚类，表明这些群体中基因型的环境偏好相似。对环境驱动因素的多变量分析发现，群落组成变化与盐度和大量营养素的相关性较高，但与混合层深度的相关性较低，混合层深度被认为是罗斯海分类组成的主要决定因素。年份之间的比较表明，海洋中的群落组成相对于陆架斜坡水域在时间上更加稳定。这项以更精细的分类分辨率对浮游植物群落组成的季节性变化进行的研究，提供了对更广泛的罗斯海的物种和菌株特异性分布、生态偏好以及与环境条件的关系的见解，为未来区域变化的建模和预测提供了信息。