胶州湾海洋生态系统国家野外研究站知识库

浮游动物是海洋浮游食物网、物质循环和能量流动的关键组成部分，其生物量水平和类群结构在很大程度上影响着碳循环的输出效率。南海北部海域是中尺度涡的高发区域，中尺度涡对海洋生态系统具有显著影响。本研究围绕南海北部陆坡海域进行了春季、夏季和秋季3个季节航次的采样，通过浮游动物图像扫描ZooScan系统分析了浮游动物的生物量水平、粒径和类群结构，结合物理水文、化学和生物参数讨论了影响南海北部陆坡浮游动物的因素。

春季，南海北部陆坡海域受到反气旋式暖涡的影响，根据遥感图像、实测温度和盐度结果将采样站位划分为暖涡内、暖涡边缘和暖涡外区域。浮游动物湿重、干重和碳生物量平均分别为43.32±20.44 mg m^-3、3.39±2.14 mg m^-3和1.36±0.83 mg C m^-3。暖涡内部浮游动物生物量显著低于暖涡边缘和暖涡外围（p<0.05）。浮游动物丰度和体积生物量平均分别为573.2±284.8 ind. m^-3和92.2±38.9 mm³ m^-3，水平分布与生物量分布基本一致，但暖涡内部和暖涡边缘差异不显著（p>0.05）。0.2-0.5 mm粒径丰度占绝对优势，平均比例64.9%，随粒径增加丰度比例逐渐降低。大粒径浮游动物体积生物量贡献率较高，2-5 mm和1-2 mm粒径浮游动物所占比例平均分别为39.5%和33.3%。暖涡内部和暖涡外围浮游动物粒径组成存在显著性差异（p<0.05）。基于丰度结果，桡足类、夜光虫和被囊类浮游动物是三大优势类群，所占比例平均分别为69.1%、7.0%和3.4%；基于体积生物量结果，桡足类、毛颚类和水母类浮游动物是三大优势类群，所占比例平均分别为52.8%、17.1%和8.3%。暖涡内部和暖涡外围浮游动物的类群组成存在显著性差异（p<0.05）。不同粒径浮游动物的类群组成存在较大的差异，小粒径浮游动物中桡足类占绝对优势，但大粒径浮游动物中桡足类比例显著降低，毛颚类和水母类的贡献比例增加。研究结果还表明，小粒径浮游动物受暖涡影响更显著，而大粒径浮游动物则存在显著的昼夜变化。桡足类、端足类和介形类浮游动物均存在昼夜变化，但只有虾类浮游动物具有显著的昼夜差异（p<0.05）。

夏季，南海北部陆坡海域受到中尺度涡对的影响，结合遥感图像和实测结果将采样站位划分为暖涡区、锋面区、冷涡区和陆架区。浮游动物湿重和干重生物量平均分别为63.55±31.92 mg m^-3和9.13±4.75 mg m^-3。浮游动物丰度和体积生物量平均分别为1328.6±842.2 ind. m^-3和156.3±100.6 mm³ m^-3，水平分布差异大，暖涡区丰度和体积生物量最低，陆架区、锋面区和冷涡区均较高，并且在冷涡区和暖涡区均存在显著性差异（p<0.05）。0.2-0.5 mm粒径丰度所占比例平均为72.4%，在锋面区和陆架区比例明显高于暖涡区；1-2 mm和2-5 mm粒径浮游动物体积生物量高，所占比例平均分别为35.9%和31.3%。基于丰度结果，桡足类、卵和夜光虫浮游动物是三大优势类群，所占比例平均分别为67.0%、4.5%和3.8%；基于体积生物量结果，桡足类、毛颚类和水母类浮游动物是三大优势类群，所占比例平均分别为50.3%、14.5%和9.6%。ANOSIM分析表明陆架区和暖涡区浮游动物的类群组成存在显著性差异（p < 0.05）。不同粒径浮游动物的类群组成存在差异，小粒径浮游动物中桡足类明显占优，随着粒径增加比例降低，大粒径中毛颚类、水母类和虾类所占比例增加。浮游动物垂直分布结果表明，丰度和体积生物量主要集中在100米以浅水层，并且浅水层小粒径浮游动物比例高，深水层大粒径比例高。

秋季，南海北部陆坡浮游动物湿重、干重和碳生物量平均分别为72.97±41.63 mg m^-3、10.41±5.07 mg m^-3和3.49±1.72 mg C m^-3，水分分布高值主要集中在西北部。浮游动物丰度和体积生物量平均分别为662.5±259.9 ind. m^-3和112.7±35.8 mm³ m^-3，体积生物量在东南部较高。0.3-0.5 mm和0.5-1 mm粒径浮游动物丰度比例高，平均分别为57.1%和35.8%；1-2 mm和2-5 mm粒径浮游动物体积生物量比例高，平均分别为33.2%和32.1%。基于丰度结果，桡足类、有孔虫和毛颚类浮游动物是优势类群，所占比例平均分别为65.3%、8.0%和4.5%；基于体积生物量结果，桡足类、毛颚类和虾类浮游动物是优势类群，所占比例平均分别为37.6%、16.4%和8.5%。小粒径中桡足类占绝对优势，随粒径增加比例降低，毛颚类、水母类和虾类比例增加。浮游动物垂直分布结果显示，丰度和体积生物量主要集中在100米以浅水层，浅水层小粒径浮游动物丰度和体积生物量比例高、深水层大粒径比例高。研究结果还表明浮游动物昼夜变化明显，浅水层浮游动物丰度和体积生物量为夜间高、白天低，而深水层则表现为夜间低、白天高的趋势，并且大粒径浮游动物昼夜变化更明显。桡足类、毛颚类和介形类浮游动物存在明显的昼夜差异，但只有虾类浮游动物体积生物量在夜间显著高于白天（p<0.05）。

总的来说，南海北部陆坡浮游动物湿重生物量和干重生物量的季节变化是秋季>夏季>春季，季节平均分别为58.65±33.16 mg m^-3和7.35±5.06 mg m^-3。浮游动物丰度和体积生物量的季节变化是夏季>秋季>春季，平均分别为872.2±645.0 ind. m^-3和121.1±71.9 mm³ m^-3。浮游动物生物量和丰度季节变化不同，主要原因是物理过程的差异，进而引起浮游动物粒径组成和类群组成的季节差异。春季研究海域受到寡营养暖涡的影响，浮游动物水平最低；而夏季由于中尺度涡对将大量珠江冲淡水携带至该海域，小粒径浮游动物比例高、胶质类浮游动物比例高，秋季恰恰相反。

Zooplankton plays key component of marine planktonic food webs, material circulation, and energy flow. The biomass and taxonomic structure of zooplankton affect largely the efficiency of carbon transportation. Mesoscale eddies have been frequently observed in the northern South China Sea (SCS) and affect the marine ecosystems. Here we focused on zooplankton and conducted three cruises in the SCS northern slope during spring, summer and autumn. Zooplankton biomass, size composition and taxonomic structure were analyzed with a ZooScan integrated system and discussed their relationships with the hydrological, chemical and chlorophyll a parameters.

In spring, an anticyclonic eddy affected the SCS northern slope. The sampling stations were divided into inside, at the edge and outside the anticyclonic eddy according to the satellite images, in-situ temperature and salinity. The zooplankton wet weight, dry weight and carbon weight were 43.32 ± 20.44 mg m^-3, 3.39 ± 2.14 mg m^-3 and 1.36 ± 0.83 mg C m^-3, respectively. The zooplankton biomass were significantly lower in the inside of anticyclonic eddy than in the edge or in the outside of anticyclonic eddy (p<0.05). The zooplankton abundance and biovolume were 573.2 ± 284.8 ind. m^-3 and 92.2 ± 38.9 mm³ m^-3, respectively. The zooplankton abundance and biovolume were significantly lower in the inside of anticyclonic eddy than in the outside of anticyclonic eddy (p<0.05). Zooplankton in the 0.2-0.5 mm size class dominated the zooplankton abundance with a mean proportion of 64.9%. The proportion of zooplankton abundance decreases with the increasing size. However, larger zooplankton contributed higher biovolume percentage compared to small organisms. The biovolume proportion in the 2-5 mm and 1-2 mm size classes were 39.5% and 33.3%, respectively. The size compositions were significantly different between the inside of anticyclonic eddy and the outside of anticyclonic eddy (p<0.05). Copepoda, Noctiluca and Tunicata dominated the zooplankton abundance, with mean proportion of 69.1%, 7.0% and 3.4%, respectively. Copepoda, Chaetognatha and Medusa dominated the zooplankton biovolume, with mean proportion of 52.8%, 17.1% and 8.3%. The taxonomic compositions were significantly different between the inside of anticyclonic eddy and the outside of anticyclonic eddy (p<0.05). The zooplankton taxonomic compositions showed different patterns between the size classes. Copepoda made a major contribution in small size classes, but with a lower contribution in large size classes. In contrast, Chaetognatha and Medusa made higher contributions in large size classes. The results indicated that the zooplankton in smaller size classes was obviously affected by the anticyclonic eddy. We also found obvious diel variations of zooplankton in the larger size classes. In addition, diel variations of Copepoda, Amphipoda and Ostracoda were observed, but only Shrimp was significantly increased during night (p<0.05).

In summer, a mesoscale dipole eddies affected the SCS northern slope. The sampling stations were divided into the anticyclonic eddy area, frontal area, cyclonic eddy area and shelf area according to the satellite images, in-situ data. The zooplankton wet weight and dry weight in SCS northern slope were 63.55 ± 31.92 mg m^-3 and 9.13 ± 4.75 mg m^-3, respectively. The zooplankton abundance and biovolume were 1328.6 ± 842.2 ind. m^-3 and 156.3 ± 100.6 mm³ m^-3, respectively. Lower zooplankton abundance and biovolume was observed in anticyclonic eddy than in shelf area, frontal area and cyclonic eddy. Significant difference of zooplankton abundance and biovolume was found between the anticyclonic eddy and the cyclonic eddy (p<0.05). The proportion of zooplankton abundance in the 0.2-0.5 mm size class was 72.4% and the proportion in shelf area and frontal area were higher than in anticyclonic eddy (p<0.05). The biovolume proportion in the 1-2 mm and 2-5 mm size classes were 35.9% and 31.3%, respectively. Copepoda, Egg and Noctiluca were the most abundant taxa, with mean proportions of 67.0%, 4.5% and 3.8%, respectively. Copepoda, Chaetognatha and Medusa dominated the zooplankton biovolume, with mean proportions of 50.3%, 14.5% and 9.6%, respectively. The ANOSIM analysis showed that the zooplankton taxonomic compositions was significantly different between the shelf area and the anticyclonic eddy (p<0.05). The zooplankton taxonomic compositions showed different patterns between the size classes. Copepoda made a major contribution in small size classes and the proportion decreases with the increasing size. In contrast, Chaetognatha, Medusa and Shrimp made higher contributions in large size classes. The vertical distribution of zooplankton abundance and biovolume showed that higher values concentrated on 0-100 m layer. Furthermore, the proportion of zooplankton in smaller size class was higher in upper layer, while the proportion of the zooplankton in larger size class was higher in deeper layer.

In autumn, the zooplankton wet weight, dry weight and carbon weight in SCS northern slope were 72.97 ± 41.63 mg m^-3, 10.41 ± 5.07 mg m^-3 and 3.49 ± 1.72 mg C m^-3, respectively. Higher zooplankton biomass was located in the northwestern regions. The zooplankton abundance and biovolume were 662.5 ± 259.9 ind. m^-3 and 112.7 ± 35.8 mm³ m^-3, respectively. Higher zooplankton biovolume was located in the southeastern regions. The proportion of zooplankton abundance in 0.3-0.5 mm and 0.5-1 mm size classes were higher, with mean proportion of 57.1% and 35.8%, respectively. The proportion of zooplankton biovolume in 1-2 mm and 2-5 mm size classes were higher, with mean proportion of 33.2% and 32.1%, respectively. Copepoda, Foraminifera and Chaetognatha were the most abundant taxa, with mean proportions of 65.3%, 8.0% and 4.5%, respectively. Copepoda, Chaetognatha and Shrimp dominated the zooplankton biovolume, with mean proportions of 37.6%, 16.4% and 8.5%, respectively. Copepoda made a much higher proportion in small size classes and the proportion decreases with the increasing size. In contrast, Chaetognatha, Medusa and Shrimp made higher contributions in large size classes. The vertical distribution of zooplankton abundance and biovolume showed that higher values concentrated on 0-100 m layer. In addition, the proportions of zooplankton abundance and biovolume in smaller size class were higher in upper layer, while the proportion of the zooplankton in larger size class was higher in deeper layer. The results also showed that the zooplankton abundance and biovolume were higher at night than at day in the upper layer, while the opposite diel variation was in the deeper layer. Furthermore, we also found obvious diel variations of zooplankton in the larger size classes. Diel variations of Copepoda, Chaetognatha and Ostracoda were observed, but only Shrimp biovolume was significantly increased at night (p<0.05).

In general, the seasonal variations of zooplankton wet weight and dry weight in the SCS northern slope were autumn > summer > spring, with averaged values of 58.65 ± 33.16 mg m^-3 and 7.35 ± 5.06 mg m^-3, respectively. The seasonal variations of zooplankton abundance and biovolume were summer > autumn > spring, with averaged values of 872.2 ± 645.0 ind. m^-3 and 121.1 ± 71.9 mm³ m^-3, respectively. The seasonal difference of zooplankton biomass and abundance was mainly due to the different physical progresses, which resulted the difference of size composition and taxonomic structure of zooplankton. The lowest zooplankton level in spring could be attributed to the anticyclonic eddy with oligotrophic conditions. In summer, the amount of fresh water of Pearl River was transported to our sampling stations due to  mesoscale dipole eddies, which associated with higher proportion zooplankton in smaller size classes and the higher proportion of gelatinous zooplankton. However, the zooplankton in autumn was just the opposite of summer.