GLOBEC 2000: Responses of the Neocalanus spp. - Microplankton Community to Physical forcing in the Coastal Gulf of Alaska

阿拉斯加湾沿海的海洋和大气条件在日、季和年际时间尺度上变化很大。包括鲑鱼在内的高营养级优势物种的丰度已被证明与这种环境变化相一致，最明显的是在十年时间尺度上。将这些大规模的人口转移与气候联系起来的机制尚不清楚，但可能涉及较低的营养级反应（即自下而上的影响）。虽然较低的营养级物种在CGOA研究较少，初步数据表明，浮游生物种群的丰度和活动也强烈响应至少短期变化CGOA的物理制度。此外，微型浮游动物可能是大陆架上浮游植物的主要消费者，从而构成初级生产力的物理强迫和更高的营养级之间的关键联系。PI将检查微型浮游生物群落的结构化过程，并将它们与新哲水蚤种群联系起来，阿拉斯加湾沿岸主要的食草桡足类。新哲水蚤属Neocalanus（N. flemingeri，新几内亚牛肝菌N. plumchrus，拟单胞菌N. cristatus）的贡献显着的总春季和夏季浮游动物生物量在CGOA。新哲水蚤能够同时食用浮游植物和微型浮游动物，尽管决定这种饮食分配的因素还不清楚。此外，这些桡足类已被证明会改变个体的大小，种群生物量和生命周期时间，以应对海洋条件的变化。最后，新哲水蚤的大小和丰度使它们成为粉红鲑鱼鱼苗和其他沿海鱼类的重要潜在猎物。因此，微型浮游生物-新哲水蚤食物网是一个潜在的场所，为翻译的环境变化到更高的营养级的反应。将进行的具体测量包括：1）微型浮游生物丰度和组成（浮游植物的大小结构、微型浮游动物的种类和大小组成）; 2）微型浮游动物食草率; 3）新哲水蚤的比率。吃微型浮游动物和浮游植物这项工作的一个新要素是使用FlowCAM（流式细胞仪和显微镜）来表征摄食实验期间的微型浮游生物丰度和群落组成。这种新的流动成像技术应该使我们能够进行更多的桡足类放牧实验，而不是完全依赖传统的显微镜。 通过在一系列的沿海物理制度和季节的采样，这项工作将测试的假设，在物理环境的变化决定生产水平和食物网结构的CGOA，改变时间，数量和质量的资源提供给新哲水蚤，并最终向其他更高的营养级物种。

Ocean and atmospheric conditions in the coastal Gulf of Alaska vary widely over daily, seasonal, and interannual time scales. The abundance of dominant upper trophic level species, including salmon, has been shown to vary in concert with this environmental change, most notably on decadal time scales. The mechanisms linking these large-scale population shifts with climate are not clear, but may involve lower trophic level responses (i.e. bottom-up effects). Although lower trophic level species are less well studied in the CGOA, preliminary data indicates that the abundance and activity of microplankton populations also respond strongly at least to short-term changes in CGOA physical regimes. Additionally, microzooplankton are likely the dominant consumers of phytoplankton on the shelf, thus consituting a key link between physical forcing of primary production and higher trophic levels. The PIs will examine the processes structuring microplankton communities and link them with populations of Neocalanus spp., the dominant particle-grazing copepods in the coastal Gulf of Alaska. Collectively, 3 species of Neocalanus (N. flemingeri, N. plumchrus, N. cristatus) contribute substantially to total spring and summer mesozooplankton biomass in the CGOA. Neocalanus are capable of consuming both phytoplankton and microzooplankton, though the factors dictating this diet partitioning are not well understood. Furthermore, these copepods have been shown to alter individual body size, population biomass, and life cycle timing in response to variations in ocean conditions. Finally, the size and abundance of Neocalanus make them an important potential prey for pink salmon fry and other coastal fish species. Thus the microplankton - Neocalanus food web is a potential locus for the translation of environmental variation into higher trophic level responses. Specific measurements to be made are: 1) Microplankton abundance and composition (phytoplankton size structure, microzooplankton species and size composition); 2) Rates of microzooplankton herbivory; and 3) Rates of Neocalanus spp. grazing on microzooplankton and phytoplankton. A novel element of the work is the use of the FlowCAM (Flow Cytometer and Microscope) to characterize microplankton abundance and community composition during feeding experiments. This new imaging-in-flow technology should allow us to conduct many more copepod grazing experiments than would be possible with complete reliance on conventional microscopy. By sampling across a range of coastal physical regimes and seasons, this work will test the hypothesis that variation in the physical environment dictates production levels and food web structure in the CGOA, altering the timing, amount and quality of resources available to Neocalanus and ultimately to other higher trophic level species.