Table_2_Differential Impact of the Khatanga and Lena (Laptev Sea) Runoff on the Distribution and Grazing of Zooplankton.docx

The ecosystems of the Arctic Ocean and their expected changes in a context of Global climate processes are crucially dependent on the freshwater input. The freshwater signal is assumed to be the main structuring factor for the marine fauna on the shallow shelf of the Siberian Arctic seas. The Laptev Sea, as a part of the world’s widest continental shelves surrounding the Arctic Ocean, is a key area for understanding the land–ocean interaction in high latitude regions. The largest freshwater input is provided by the deltaic Lena river followed by the estuarine Khatanga river. The plumes of these rivers differ considerably in their hydrophysical characteristics, suggesting differential impacts on ecosystems of the adjacent shelf. The key component of pelagic ecosystems is zooplankton, which transfers energy from primary producers to higher trophic levels and modifies sedimentations processes. This study is focused on the influence of river discharge on zooplankton in the Laptev Sea at the end of productive season. We studied zooplankton biomass, species composition, distribution patterns of the dominant species and assessed herbivorous feeding rates and grazing pressure of these species along a transect from the inner Khatanga Gulf northward to the continental slope, and a transect in the Lena plume influenced area in August-September 2017. Despite large spatial extension of the Khatanga plume, the impact of river discharge on zooplankton species composition was restricted mainly to the inner Gulf where the brackish species shaped the community. Contrary to the Khatanga input, the Lena freshwater inflow was highly variable and under certain conditions (discharge rate, wind forcing) governed the structure of zooplankton community over a vast shelf area. Distribution patterns of zooplankton biomass, ingestion rates and grazing impact of the dominant species on phytoplankton over the shelf influenced by the Khatanga and Lena plumes were similar. Analysis of our results on demographic structure of Calanus glacialis suggests that seasonal development of the population was largely controlled by the time of ice retreat. Observed climatic changes in the Arctic were not reflected in the total zooplankton biomass and composition of the dominant species.

北极海洋生态系统及其在全球气候进程中的预期变化，其关键性依赖于淡水资源输入。淡水信号被视为西伯利亚北极海域浅滩海域海洋生物群落的主要结构化因素。拉普捷夫海，作为环绕北极海洋最广阔的大陆架的一部分，是理解高纬度地区陆地-海洋相互作用的关键区域。最大的淡水输入由勒拿河三角洲提供，其次是哈坦加河口。这些河流的羽流在水文物理特性上存在显著差异，表明其对相邻大陆架生态系统的不同影响。浮游生物生态系统的主要组成部分是浮游动物，它们将初级生产者转移的能量传递到更高营养级，并改变沉积过程。本研究聚焦于河流径流对拉普捷夫海浮游动物在生长期末的影响。我们研究了浮游动物生物量、物种组成、优势物种的分布模式，并评估了这些物种的草食性摄食率和放牧压力，这些研究是在2017年8月至9月期间，从哈坦加湾内部向北至大陆坡的横断面以及受勒拿河羽流影响的区域进行的。尽管哈坦加羽流的时空范围较大，但河流径流对浮游动物物种组成的影响主要局限于内部海湾，其中咸淡水物种构成了群落。与哈坦加的输入相反，勒拿河的淡水流入量高度多变，在特定条件下（径流速率、风力驱动）决定了广阔大陆架区域浮游动物群落的结构。受哈坦加和勒拿羽流影响的浮游动物生物量分布、摄食速率以及优势物种对浮游植物的放牧影响模式相似。我们对Calanus glacialis种群结构的研究结果表明，该种群的季节性发展主要受冰撤退时间控制。观察到的北极气候变化并未在总浮游动物生物量和优势物种组成中体现。