Functional groups have become an important tool for characterizing communities of marine and estuarine environments. Their use also holds promise for a better understanding of the temporal dynamics of phytoplankton. This study aimed to evaluate the contributions of phytoplankton size fractions and functional groups characterizing short‐term variation throughout tidal cycles and between dry and rainy seasons in a tropical estuarine system. Camamu Bay is an oligotrophic estuarine system that is under strong influence from tropical shelf waters and is characterized by high salinity and low concentrations of dissolved nutrients. Surface‐water samples were collected at nine sampling sites distributed among the three hydrodynamic regions of the bay, and at a mooring, at 3‐hr intervals during tidal cycles (12 hr each) in both the rainy and the dry season. Although the abundances of the phytoplankton fractions (pico‐, nano‐, and micro‐) were higher in the rainy season and during periods of higher tide, they were not significantly higher. The phytoplankton community in the bay comprises three functional groups: GI = “colonial” (i.e., chain‐forming diatoms and filamentous cyanobacteria); GII = “GALD >40” (i.e., pennate and centric diatoms with MDL >40 µm), and GIII = “flagellates” (i.e., species with motility via flagella). Nanoflagellates were the most abundant form in the bay, while chain‐forming diatoms, in particular, contributed to the microphytoplankton fraction during both the rainy and dry seasons. Functional groups, as defined by cluster analysis, reflected ecological strategies compatible with the high hydrodynamics of Camamu Bay, which is characterized by processes of tidal‐forced intense mixing, mainly during periods of spring tides. The phytoplankton of the bay was found to possess a series of attributes (functional traits) that endow them with some resistance to sinking. Functional diversity indexes (FEve, FDiv, and FDis) indicated a stable community without significant short‐term variation due to low variability in the environmental conditions of the system during the study period.

中文翻译：

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浮游植物功能群：热带潮汐强迫河口系统中的短期变化

职能团体已成为表征海洋和河口环境群落的重要工具。它们的使用也有望更好地了解浮游植物的时间动态。这项研究旨在评估在热带河口系统中，整个潮汐周期以及旱季和雨季之间浮游植物的大小比例和功能组的特征。卡马穆湾是一种营养贫化的河口系统，受到热带陆架水域的强烈影响，其特征是盐度高，溶解营养物浓度低。在雨季和旱季，在潮汐周期（每个12个小时）中，以3个小时的间隔（分布在海湾三个水动力区域之间）的九个采样点采集了地表水样本。尽管在雨季和涨潮时浮游植物的丰度（微微，纳微和微）较高，但并没有明显提高。海湾中的浮游植物群落包括三个功能组：GI =“殖民地”（即成链的硅藻和丝状蓝细菌）；GII =“ GALD> 40”（即MDL> 40 µm的羽状和中心硅藻），GIII =“鞭毛”（即具有鞭毛活力的物种）。纳米鞭毛虫是海湾中最丰富的形式，而在雨季和旱季，链状硅藻尤其有助于浮游植物的微生。聚类分析所定义的官能团反映了与卡马穆湾高水动力相适应的生态策略，其特征是潮汐强迫强烈混合的过程，主要是在春季潮汐时期。发现海湾的浮游植物具有一系列属性（功能性状），使它们对下沉有一定的抵抗力。功能多样性指数（FEve，FDiv和FDis）表明，由于研究期间系统环境条件的可变性较低，因此社区稳定且没有明显的短期变化。