Abstract The phytoplankton in coastal regions are responding to constant environmental changes, thus the use of proxies derived from in situ frequent time-series observations and validated from traditional microscopic or pigment methods can be a solution for detecting rapid responses of community dynamics and succession. In this study, we combine in situ high-frequency (every 30 min from May to September 2017) optical and hydrographic data from a moored buoy and weekly discrete sampling to track phytoplankton community dynamics and succession in Mausund Bank, a highly productive region of the coast of Norway. Three hydrographic regimes were observed: mixing period (MP) in spring, onset of stratification (transient period, TP) in summer and a stratified period (SP) in fall, with occasional strong winds that disrupted the surface stratification in the beginning of September. A bloom dominated by the diatom Skeletonema costatum was observed in MP due to intense mixing and nutrient availability, while flagellates prevailed in nutrient-poor waters during the TP, followed by a bloom dominated by rhizosolenid diatoms (Proboscia alata and Guinardia delicatula), when stratification peaked. A mixed assemblage of diatoms (e.g. Pseudo-nitzschia), coccolithophores and dinoflagellates occurred during SP, as strong winds reintroduced nutrients to surface waters. Through pigment (chemotaxonomy) and microscopic observations, we tested, for the first time in a coastal region, whether an ‘optical community index’ derived from in situ measurements of chlorophyll a fluorescence (Fchla) and optical particulate backscattering (bbp) is suitable to differentiate between diatom versus flagellate dominance. We found a negative relationship between Fchla:bbp and diatoms:flagellate, contrary to previous observations, possibly because of the influence of non-algal contribution (e.g. zooplankton, fecal pellets and detritus) to the bbp pool in highly productive systems. This finding suggests that such relationship is not universal and that other parameters are needed to refine the optical community index in coastal regions.

中文翻译：

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使用光学方法的浮游植物群落演替和动态

摘要 沿海地区的浮游植物对环境的不断变化做出反应，因此使用来自原位频繁时间序列观测并通过传统微观或色素方法验证的代理可以成为检测群落动态和演替快速响应的解决方案。在这项研究中，我们结合了来自系泊浮标的原位高频（2017 年 5 月至 9 月每 30 分钟一次）光学和水文数据和每周离散采样，以跟踪 Mausund Bank 的浮游植物群落动态和演替。挪威海岸。观察到三种水文状况：春季混合期（MP），夏季分层开始（瞬态期，TP）和秋季分层期（SP），9 月初偶有强风扰乱了地表分层。由于强烈的混合和养分可用性，在 MP 中观察到以硅藻 Skeletonema costatum 为主的水华，而在 TP 期间，鞭毛虫在营养贫乏的水域中盛行，然后在分层时以根茎硅藻（Proboscia alata 和 Guinardia delicatula）为主达到顶峰。由于强风将营养物质重新引入地表水，因此在 SP 期间出现了硅藻（例如 Pseudo-nitzschia）、颗石藻和甲藻的混合组合。通过色素（化学分类）和显微镜观察，我们首次在沿海地区进行了测试，来自叶绿素 a 荧光 (Fchla) 和光学颗粒反向散射 (bbp) 的原位测量的“光学群落指数”是否适合区分硅藻与鞭毛虫优势。我们发现 Fchla:bbp 和硅藻:flagellate 之间存在负相关关系，这与之前的观察相反，可能是因为非藻类贡献（例如浮游动物、粪便颗粒和碎屑）对高产系统中 bbp 池的影响。这一发现表明这种关系并不普遍，需要其他参数来完善沿海地区的光学群落指数。可能是因为非藻类贡献（例如浮游动物、粪便颗粒和碎屑）对高生产力系统中 bbp 池的影响。这一发现表明这种关系并不普遍，需要其他参数来完善沿海地区的光学群落指数。可能是因为非藻类贡献（例如浮游动物、粪便颗粒和碎屑）对高生产力系统中 bbp 池的影响。这一发现表明这种关系并不普遍，需要其他参数来完善沿海地区的光学群落指数。