Seasonal studies on size-fractionated phytoplankton productivity (biomass and primary production), marker pigments, and species composition and abundance were carried out in the Cochin estuary (CE), located on the southwest coast of India, to identify the critical environmental factors that control the consistent preponderance of diatoms. The overall results of the study showed a significant contribution of small-sized phytoplankton, specifically nanophytoplankton (2–20 µm), to the total chlorophyll a and primary production in the estuary, regardless of seasons. Diatoms constituted the major phytoplankton taxa, showed an exceptional seasonal scale increase in numerical abundance during the post-southwest monsoon. The relative increase in fucoxanthin (biomarker of diatoms) over other marker pigments substantiated the numerical dominance of diatoms throughout the sampling periods. This is the first study in the CE in which phytoplankton marker pigments have been detected and elucidated the seasonality of functional groups based on HPLC/chemotaxonomy analytical approaches. The prevalence of high Diat_DP and diatom chlorophyll a equivalent (estimated by CHEMTAX), further confirmed the preponderance of diatoms in the CE, despite the intermittent dominance of cyanophytes and cryptophytes (monsoon period). The consistent increase in SPM levels (> 25 mg L^–1), established at all sampling stations, indicated that the water column turbidity might be one of the significant environmental factors hindering the growth of large-sized phytoplankton (ca. >20 µm) in the CE even if the system invariably holds high inorganic nutrients, irrespective of seasons.

在位于印度西南海岸的科钦河口 (CE) 进行了对大小分级浮游植物生产力（生物量和初级生产）、标记色素以及物种组成和丰度的季节性研究，以确定控制浮游植物的关键环境因素硅藻的持续优势。研究的总体结果表明小型浮游植物，特别是纳米浮游植物 (2-20 µm) 对总叶绿素a和河口的初级生产，不分季节。硅藻构成了主要的浮游植物分类群，在后西南季风期间数量丰度表现出异常的季节性增加。岩藻黄质（硅藻的生物标志物）相对于其他标志颜料的相对增加证实了硅藻在整个采样期间的数量优势。这是 CE 中的第一项研究，其中已检测到浮游植物标记色素，并基于 HPLC/化学分类学分析方法阐明了官能团的季节性。高Diat _DP和硅藻叶绿素a的流行等效（由 CHEMTAX 估计），进一步证实了 CE 中硅藻的优势，尽管蓝藻和隐藻（季风期）间歇性占优势。在所有采样站建立的SPM 水平（> 25 mg L ^–1）的持续增加表明水柱浊度可能是阻碍大型浮游植物（约 >20 µm）生长的重要环境因素之一在 CE 中，即使系统总是保持高无机养分，无论季节如何。