Ecological boundaries constrain pro- and eukaryotic richness: from the ice edge to the equator in the Pacific Ocean@en

Marine microbes along with micro eukaryotes are key regulators of oceanic biogeochemical pathways. Here we present a high-resolution (every 0.5° latitude) dataset describing microbial pro- and eukaryotic diversity, in the surface and just below the thermocline, along a 7000km transect from 66° S at the Antarctic ice edge to the equator in the South Pacific Ocean. The transect, conducted in Austral winter, covered key oceanographic features including crossing of the polar front (PF), the subtropical front (STF) and the equatorial upwelling region. Our data indicate that temperature does not determine patterns of marine microbial richness, complementing the global model data from Ladau, et al. (2013). Rather, NH4⁺ nanoplankton and primary productivity were the main drivers for archaeal and bacterial richness. Eukaryote richness was highest in the least productive ocean region, the tropical oligotrophic province. We also observed a novel diversity pattern in the South Pacific Ocean; a regional increase in archaeal and bacterial diversity between 10° S and the equator. Our data showed that the mean latitudinal ranges of archaea and bacteria decreased with latitude, thereby not confirming the Rapoport's rule. We show that permanent oceanographic features, such as the STF and the equatorial upwelling can have a significant influence on pro- and eukaryotic richness.海洋微生物与微型真核生物是海洋生物地球化学循环的关键调控者。本研究发布一套高分辨率（纬度采样间隔0.5°）数据集，记录了沿南太平洋7000公里调查断面——从南极冰缘南纬66°延伸至赤道——的表层水体及温跃层（thermocline）下方的微生物原核与真核多样性信息。该调查于南半球冬季开展，覆盖了极锋（polar front, PF）、副热带锋（subtropical front, STF）与赤道上升流区等关键海洋学特征。研究数据表明，温度并非海洋微生物物种丰富度格局的决定因素，这一结论与Ladau等人2013年的全球模型研究结果互为补充。与之相反，铵态氮（NH₄⁺）与纳米浮游生物、初级生产力才是古菌与细菌物种丰富度的主要驱动因子。真核生物物种丰富度在生产力最低的热带寡营养海域达到峰值。本研究还在南太平洋观测到一种全新的多样性分布格局：在南纬10°至赤道区域，古菌与细菌多样性呈现区域性升高趋势。数据显示，古菌与细菌的平均纬度分布范围随纬度升高而缩小，这一结果并不支持拉波波特法则（Rapoport's rule）。本研究证实，副热带锋（STF）与赤道上升流区这类永久性海洋学特征，可对原核与真核生物的物种丰富度产生显著影响。