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

阿拉斯加湾沿岸的海洋和大气条件在每日、季节和年际时间尺度上变化很大。包括鲑鱼在内的高营养层优势物种的丰度已被证明与这种环境变化相一致，最显著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水平反应(即自下而上的效应)。虽然低营养级物种在CGOA中的研究较少，但初步数据表明，微型浮游生物种群的丰度和活动至少对CGOA物理制度的短期变化也有强烈的反应。此外，微型浮游动物很可能是大陆架上浮游植物的主要消费者，因此在初级生产力的物理强迫和更高的营养水平之间构成了关键环节。PIS将研究微型浮游生物群落的结构过程，并将它们与阿拉斯加湾沿岸的优势颗粒食草型桡足类动物Neocalanus spp.的种群联系起来。总体而言，在CGOA中，3种Neocalanus(N.flemingeri，N.pletchus，N.criatus)对春季和夏季中浮游动物的总生物量有很大贡献。Neocalanus能够同时捕食浮游植物和微型浮游动物，尽管决定这种食物分配的因素还不是很清楚。此外，这些桡足类已被证明可以改变个体的身体大小、种群生物量和生命周期时间，以应对海洋条件的变化。最后，新鲑鱼的大小和数量使其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-新钙藻类食物网是将环境变化转化为更高营养级反应的潜在场所。将进行的具体测量包括：1)微型浮游生物的丰度和组成(浮游植物的大小结构、微型浮游动物种类和大小组成)；2)微型浮游动物的食草率；以及3)新卡兰氏藻的比率。捕食微型浮游动物和浮游植物。这项工作的一个新元素是使用FlowCAM(流动细胞仪和显微镜)来表征喂养实验中的微浮游生物丰度和群落组成。这种新的流动成像技术应该可以让我们进行比完全依赖传统显微镜更多的桡足类放牧实验。通过对一系列沿海物理状态和季节的采样，这项工作将检验这样一个假设，即物理环境的变化决定了CGOA中的生产水平和食物网络结构，改变了可供新卡纳鱼并最终提供给其他较高营养级别物种的资源的时间、数量和质量。

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.