Abstract Heterotrophic flagellates (HF) play an essential function in the microbial food loops as it is an agent of biochemical cycling of limiting nutrients and being a useful bio-indicator of environmental changes. However, in spite of its profound role in aquatic ecosystem studies regarding the evaluation of the spatial and seasonal patterns of the flagellate communities are lacking in Bangladeshi water, and therefore, study on community pattern of HF in a tropical river like Padma River could be a best example for other tropical rivers of the world. The present investigation was performed with the primary objectives to evaluate flagellate community structure, their spatial and seasonal distribution patterns, and the role of hydro-biological and physicochemical variables in determining their variability. The study was conducted at selected four study sites in Padma river, Bangladesh for a period of two distinct season (dry and wet season) in 2018. Standard procedures were followed in collecting, analyzing and interpreting of sampled data. The study revealed a total of 18 genera with different degrees of specificity to hydro-biological and physicochemical variables. It further establishes significant seasonal patterns, rather than spatial differences in the distribution of the flagellate communities. We found that the higher precipitation intensity during monsoon was the critical determinant in hydrological, biological, and physicochemical fluctuations which caused a significant decline in the value of the above variables. Likewise, total phytoplankton, zooplankton, and total heterotrophic bacterial abundance was also declined five-folds during the wet season. Similarly, total abundance of HF showed a significant decline in the community during the wet season. Genus wise relative abundance (RA%) of Euglena (23.81 %) was the highest during the dry season. In conclusion, this research and data analysis techniques propose unique insights on the flagellate links to environmental and hydro-biological regime in a tropical river with global implications.

中文翻译：

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热带河流鞭毛虫群落的季节和空间变化

摘要 异养鞭毛虫 (HF) 在微生物食物循环中发挥着重要作用，因为它是限制营养物质的生化循环的媒介，也是环境变化的有用生物指标。然而，尽管在孟加拉国水域中缺乏鞭毛虫群落空间和季节格局评估的水生生态系统研究中的深刻作用，因此，研究帕德玛河等热带河流中的 HF 群落格局可能是一个世界其他热带河流的最佳范例。本调查的主要目的是评估鞭毛虫群落结构、它们的空间和季节性分布模式，以及水生生物和物理化学变量在确定其变异性中的作用。该研究于 2018 年在孟加拉国帕德玛河的选定四个研究地点进行，为期两个不同的季节（旱季和雨季）。在收集、分析和解释采样数据时遵循标准程序。该研究揭示了共有 18 个属，对水生生物和物理化学变量具有不同程度的特异性。它进一步建立了显着的季节性模式，而不是鞭毛虫群落分布的空间差异。我们发现季风期间较高的降水强度是水文、生物和物理化学波动的关键决定因素，导致上述变量的值显着下降。同样，总浮游植物、浮游动物、在雨季，异养细菌的总丰度也下降了五倍。同样，在雨季，群落中 HF 的总丰度显着下降。眼虫属的相对丰度 (RA%) (23.81%) 在旱季最高。总之，这项研究和数据分析技术对鞭毛虫与具有全球影响的热带河流中的环境和水生生物制度的联系提出了独特的见解。