Trondheim Biological Station, Department of Biology, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
Centre of Autonomous Marine Operations and Systems (AMOS), Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
PLoS One. 2022 Sep 6;17(9):e0273874. doi: 10.1371/journal.pone.0273874. eCollection 2022.
Plankton distributions are remarkably 'patchy' in the ocean. In this study, we investigated the contrasting phytoplankton-zooplankton distributions in relation to wind mixing events in waters around a biodiversity-rich island (Runde) located off the western coast of Norway. We used adaptive sampling from AUV and shipboard profiles of in-situ phytoplankton photo-physiology and particle identification (copepods, fecal pellets and the dinoflagellate Tripos spp.) and quantification using optical and imaging sensors. Additionally, traditional seawater and net sampling were collected for nutrient and in-vitro chlorophyll a concentrations and phytoplankton and meso-zooplankton abundances. Persistent strong wind conditions (~5 days) disrupted the stratification in offshore regions, while stratification and a subsurface chlorophyll maximum (SCM) were observed above the base of the mixed layer depth (MLD ~30 m) in inshore waters. Contrasting phytoplankton and zooplankton abundances were observed between inshore (with the presence of a SCM) and offshore waters (without the presence of a SCM). At the SCM, phytoplankton abundances (Tripos spp., the diatom Proboscia alata and other flagellates) were half (average of 200 cell L-1) of those observed offshore. On the contrary, meso-zooplankton counts were ~6× higher (732 ind m-3 for Calanus spp.) inshore (where a SCM was observed) compared to offshore areas. In parallel, fecal pellets and ammonium concentrations were high (>1000 ind m-3 for the upper 20 m) at the SCM, suggesting that the shallow mixed layer might have increased encounter rates and promoted strong grazing pressure. Low nutrient concentrations (< 1μM for nitrate) were found below the MLD (60 m) in offshore waters, suggesting that mixing and nutrient availability likely boosted phytoplankton abundances. The size of the absorption cross-section (σPII') and yield of photosystem II photochemistry under ambient light (φPII') changed according to depth, while the depth-related electron flow (JPII) was similar between regions, suggesting a high degree of community plasticity to changes in the light regime. Our results emphasize the importance of using multiple instrumentation, in addition to traditional seawater and net sampling for a holistic understanding of plankton distributions.
浮游生物在海洋中的分布非常“不均匀”。在这项研究中，我们调查了与挪威西海岸外一个生物多样性丰富的岛屿（伦德岛）周围水域的风生混合事件有关的浮游植物-浮游动物的对比分布。我们使用 AUV 自适应采样和船上原位浮游植物光生理和颗粒识别（桡足类、粪便颗粒和双鞭甲藻属 Tripos 种）的剖面，并使用光学和成像传感器进行定量。此外，还收集了传统的海水和网采水样，用于测量营养物和体外叶绿素 a 浓度以及浮游植物和中型浮游动物的丰度。持续的强风条件（约 5 天）扰乱了近海地区的分层，而在混合层深度（约 30 米）之下的近岸水域则出现了分层和次表层叶绿素最大值（SCM）。在近岸（存在 SCM）和近海（不存在 SCM）水域观察到浮游植物和浮游动物的丰度存在明显差异。在 SCM 处，浮游植物丰度（双鞭甲藻属 Tripos 种、硅藻 Proboscia alata 和其他鞭毛藻）为近海观测值的一半（平均为 200 个细胞 L-1）。相反，在观测到 SCM 的近岸地区，中型浮游动物的数量约高 6 倍（Calanus spp. 为 732 个 ind m-3）。与此同时，在 SCM 处，粪便颗粒和氨浓度很高（上层 20 米超过 1000 个 ind m-3），表明浅层混合层可能增加了接触率并促进了强烈的摄食压力。在离岸水域的混合层深度（60 米）以下发现了低营养浓度（硝酸盐<1μM），这表明混合和营养供应可能促进了浮游植物的丰度。在环境光下，光系统 II 光化学的吸收截面大小（σPII'）和产量（φPII'）随深度而变化，而区域之间的电子流（JPII）相似，这表明群落对光照条件变化具有高度的可塑性。我们的研究结果强调了除传统的海水和网采水样外，还需要使用多种仪器来全面了解浮游生物的分布。
