Abstract The present study addresses the copepods size structure in different phases of a cold-core eddy based on a 17 day time-series measurement (21st February to 8th March 2016) from a coastal site in the western Bay of Bengal during the Spring Intermonsoon (SIM). Copepod size measured using FlowCAM and microscope was converted into biovolumes. Based on the salinity and temperature in discrete depth layers, sampling days were grouped into 3 Phases, pre-eddy (21–24 February), Core-eddy (28 February – 6 March) and transition (25–27 February and 7–8 March). The core-eddy phase was characterised as cool, less oxygenated and nutrient-rich in subsurface layers than pre-eddy and transition. Copepod abundance and total biovolume were relatively high in core-eddy phase compared to other phases. Copepods biovolumes were arranged in 15 size classes. Contribution of each size classes in total biovolume differed between the eddy phases. In total biovolume, smaller copepods (biovolume size class ≤ log2 (−3) mm−3) contribution was high (76.84%) in pre-eddy, but larger copepods proportion was high in core-eddy phase. Normalised Abundance Size Spectra (NASS) slope varied from −2.45 to −1.02. Similar to the taxonomic diversity, size diversity also high in core-eddy phase. Relatively flatter slope, high intercept and diversity in core-eddy phase suggest that copepods production and trophic efficiency was substantially increased. In short, copepods taxonomy and their size structure explain, pre-eddy contains the smaller coastal forms and core-eddy have a mixture of smaller coastal, larger oceanic and Oxygen Minimum Zone (OMZ) tolerant forms. Larger oceanic and OMZ tolerant forms in core-eddy phase indicate their entry through the transverse of the offshore formed cold-core eddy in the study site. Slope, intercept of NASS and size diversity captured the copepod species composition and production differences between the eddy phases in terms of abundance. This study suggests plankton size spectra and size diversity can be used as a tool to predict the plankton food web response in the varying environmental conditions. This study is the first of its kind explaining about copepods size structure and size spectrum changes with the hydrographical characteristics in Indian waters.

中文翻译：

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冷核涡旋各个阶段的桡足类尺寸结构 - 归一化丰度尺寸光谱 (NASS) 方法。

摘要 本研究基于春季季候风期间孟加拉湾西部沿海地区的 17 天时间序列测量（2016 年 2 月 21 日至 3 月 8 日），研究了冷核涡流不同阶段桡足类的大小结构。 SIM）。使用 FlowCAM 和显微镜测量的桡足类大小被转换为生物体积。根据离散深度层的盐度和温度，采样天数分为 3 个阶段，前涡（2 月 21 日至 24 日）、核心涡流（2 月 28 日至 3 月 6 日）和过渡（2 月 25 日至 27 日和 7 日至 8 日）行进）。与涡流前和过渡相相比，核心涡流阶段的特点是凉爽、含氧量少、地下层营养丰富。与其他阶段相比，核心涡流阶段的桡足类丰度和总生物量相对较高。桡足类生物量按 15 个大小等级排列。每个尺寸类别在总生物量中的贡献在涡流阶段之间有所不同。在总生物量中，较小的桡足类（生物量大小等级≤ log2（-3）mm-3）在前涡中的贡献较高（76.84％），但在核心涡相中较大的桡足类比例较高。归一化丰度大小光谱 (NASS) 斜率从 -2.45 到 -1.02 不等。与分类多样性相似，核心涡旋阶段的大小多样性也很高。相对平坦的坡度、高截距和核心涡流阶段的多样性表明桡足类的生产和营养效率显着提高。简而言之，桡足类分类学及其大小结构说明，前涡流包含较小的海岸形式，核心涡流包含较小的海岸形式、较大的海洋和最低氧区 (OMZ) 耐受形式。核涡相中较大的海洋和 OMZ 耐受形式表明它们是通过研究地点的离岸形成的冷核涡的横向进入的。坡度、NASS 截距和大小多样性捕获了桡足类物种组成和涡流阶段之间在丰度方面的生产差异。这项研究表明，浮游生物大小光谱和大小多样性可用作预测不同环境条件下浮游生物食物网响应的工具。本研究首次解释了印度水域桡足类的大小结构和大小谱随水文特征的变化。NASS 和大小多样性的截距捕获了桡足类物种组成和涡流阶段之间在丰度方面的生产差异。这项研究表明，浮游生物大小光谱和大小多样性可用作预测不同环境条件下浮游生物食物网响应的工具。本研究首次解释了印度水域桡足类的大小结构和大小谱随水文特征的变化。NASS 和大小多样性的截距捕获了桡足类物种组成和涡流阶段之间在丰度方面的生产差异。这项研究表明，浮游生物大小光谱和大小多样性可用作预测不同环境条件下浮游生物食物网响应的工具。本研究首次解释了印度水域桡足类的大小结构和大小谱随水文特征的变化。