Garg Shriya, Gauns Mangesh
CSIR- National Institute of Oceanography, Goa, 403004, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India.
CSIR- National Institute of Oceanography, Goa, 403004, India; Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India.
Mar Environ Res. 2025 Oct;211:107434. doi: 10.1016/j.marenvres.2025.107434. Epub 2025 Aug 8.
Autotrophic picoplankton are integral to marine ecosystems, contributing nearly half of oceanic primary productivity, particularly in warm, oligotrophic regions. Given that subsurface chlorophyll maxima (SCM) account for over 80 % of depth-integrated primary production, this study aimed to explore the variations in picophytoplankton community composition at the SCM under dynamic environmental conditions in the Northern Indian Ocean, using flow cytometry and chemotaxonomy. We found that picophytoplankton dominated the SCM (∼60 %), with picochlorophytes being the most prevalent group (∼50 %). Picochlorophytes showed an inverse relationship with nitrate concentrations and a positive relationship with photosynthetically active radiation (PAR), suggesting their dominance in SCMs of oligotrophic and stratified regions, with higher light availability (PAR > 3 Emd). As PAR reduced, Synechococcus and picocryptophytes increased (collectively accounting for 50 % of picophytoplankton community), indicating their significant presence in SCMs with lower light conditions. These groups are well-adapted to low-light environments due to the presence of the green light-harvesting pigment phycoerythrin and their capacity for photoacclimation. In the SCM of coastal regions, we observed a shift toward microphytoplankton dominance (80 %), especially diatoms, which flourish in conditions with greater light availability and nutrient concentrations. Prochlorophytes, on the other hand, were more abundant in SCMs of warmer (> 28 °C) and highly oligotrophic waters (nitrate < 1 μM). With picophytoplankton contribution expected to increase in ocean warming scenario, our study concludes that they undergo complex changes in response to dynamic environmental conditions, which could have substantial impacts on marine ecosystems and biogeochemical cycles.
自养微微型浮游生物是海洋生态系统的重要组成部分，贡献了近一半的海洋初级生产力，特别是在温暖的贫营养区域。鉴于次表层叶绿素最大值（SCM）占深度积分初级生产的80%以上，本研究旨在利用流式细胞术和化学分类法，探索北印度洋动态环境条件下SCM处微微型浮游植物群落组成的变化。我们发现微微型浮游植物在SCM中占主导地位（约60%），其中微微型绿藻是最普遍的类群（约50%）。微微型绿藻与硝酸盐浓度呈负相关，与光合有效辐射（PAR）呈正相关，这表明它们在贫营养和分层区域的SCM中占主导地位，且光照可用性较高（PAR>3 Emd）。随着PAR降低，聚球藻属和微微型隐藻增加（共同占微微型浮游植物群落的50%），这表明它们在光照条件较低的SCM中大量存在。由于存在绿色光捕获色素藻红蛋白以及它们的光适应能力，这些类群非常适应低光照环境。在沿海地区的SCM中，我们观察到向微型浮游植物主导地位的转变（80%），特别是硅藻，它们在光照可用性和营养浓度较高的条件下大量繁殖。另一方面，原绿球藻在温度较高（>28°C）和高度贫营养水域（硝酸盐<1μM）的SCM中更为丰富。鉴于在海洋变暖情景下微微型浮游植物的贡献预计会增加，我们的研究得出结论，它们会因动态环境条件而发生复杂变化，这可能会对海洋生态系统和生物地球化学循环产生重大影响。
