The dynamics of picophytoplankton, a vital component of the aquatic microbial food web, are least explored in the river-dominated estuaries, especially those subjected to human modifications that can alter the hydrodynamics and the biota. Here, picophytoplankton community dynamics was assessed seasonally and spatially in the tropical monsoon-influenced Hooghly River estuary and an adjacent semi-enclosed dock. We hypothesized that the seasonal and spatial picophytoplankton community structure and abundance would be controlled by synergistic effects of the environmental and hydrographic factors with different responses in the semi-enclosed water body compared to the flowing estuary. The relatively lower turbidity and higher water transparency suggest that the dock's water residence time was relatively longer than the estuary due to its semi-enclosed nature. A phycocyanin-rich Synechococcus group dominated the community seasonally and spatially throughout the study region, with the highest population during the pre-monsoon. The higher water temperature, salinity, transparency, and residence time were the supporting factors. During the warm monsoon season, the relatively lower abundance of the phycocyanin-rich Synechococcus group despite the high nutrient concentrations implied impairment of growth due to high turbidity, low light availability, and residence time. However, the relatively higher salinity, water transparency, lower turbidity due to a longer residence time failed to stimulate the picophytoplankton during the cooler post-monsoon, suggesting temperature as the main controlling factor. Seasonal introduction of phycoerythrin-rich Synechococcus and two other picocyanobacteria (freshwater Microcystis and Cyanobium like) groups ensued from the open sea and river, respectively, due to varying hydrodynamics. The presence of the latter picocyanobacteria group during non-monsoon indicates higher salinity tolerance. Among the two zones, the higher abundance of picophytoplankton in the dock implies the stimulatory effect of the relatively higher water transparency, longer residence time, and enhanced resource utilization capabilities. A synergistic role of environmental parameters and hydrodynamics becomes apparent from these observations, thereby supporting the hypothesis.

微型浮游植物是水生微生物食物网的重要组成部分，在以河流为主导的河口中探索最少，特别是那些受到人类改造的河口，可以改变水动力和生物群。在这里，在受热带季风影响的胡格利河河口和相邻的半封闭码头中，对微型浮游植物群落动态进行了季节性和空间评估。我们假设与流动的河口相比，半封闭水体中具有不同响应的环境和水文因素的协同效应控制季节性和空间微型浮游植物群落结构和丰度。相对较低的浊度和较高的水透明度表明码头' 由于其半封闭性，其在水的停留时间比河口长。富含藻蓝蛋白聚球藻群在整个研究区域的季节性和空间上占主导地位，在季风前人口最多。较高的水温、盐度、透明度和停留时间是支持因素。在温暖的季风季节，尽管营养浓度高，但富含藻蓝蛋白的聚球藻的丰度相对较低，这意味着由于高浊度、低光照和停留时间而导致生长受损。然而，相对较高的盐度、水的透明度、由于较长的停留时间导致的较低的浊度未能在较冷的后季风期间刺激微型浮游植物，表明温度是主要的控制因素。季节性引入富含藻红蛋白的聚球藻由于不同的流体动力学，分别从公海和河流中产生了另外两个微微蓝藻（淡水微囊藻和蓝藻类）群。非季风期间后一种微微蓝藻群的存在表明更高的耐盐性。在这两个区域中，码头中较高的微型浮游植物丰度意味着相对较高的水透明度、较长的停留时间和增强的资源利用能力的刺激作用。从这些观察中，环境参数和流体动力学的协同作用变得明显，从而支持了这一假设。