ABSTRACT: Tidally controlled river plumes form distinct frontal boundaries that can alter the spatial distributions of larval fishes and their planktonic prey and predators. Variable in nature, they may expose larval fishes to different trophic environments over small spatio-temporal scales, with unknown consequences for survival and recruitment. In the northern California Current, the Columbia River Plume is strongly influenced by twice-daily freshwater injections that create a highly dynamic coastal environment. Using the In situ Ichthyoplankton Imaging System, we examined changes in the fine-scale horizontal and vertical distributions of larval fishes, their prey, and their predators over space and time (ebb/flood tide). In total, 6095 fish larvae and ~1.5 million prey/predator zooplankton were imaged and measured. Plume regions provided substantially higher concentrations of prey and enhanced spatial overlap between larval fishes and their prey relative to oceanic waters. The functionality of river plumes as a refuge from predators was less clear. Predator concentrations were also higher in plume regions, but overlap with larval fishes was taxon-specific and varied with the tide. Notably, regions of high zooplankton concentrations did not necessarily confer high spatial overlap on small scales (meters vertical, kms horizontal) relevant to trophic interactions. Surface salinity and chlorophyll a were the most important factors influencing the spatial overlap of zooplankton with larval fishes. In the vicinity of river plumes, larval fishes experience a diversity of unique prey and predator fields over short spatio-temporal scales, which likely contribute to variable growth and mortality patterns at much finer scales than previously thought.

中文翻译：

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随潮而变：经过精心调制的河羽附近有细小幼体鱼的猎物可利用性和捕食压力

摘要：潮汐控制的河羽形成明显的额叶边界，可以改变幼体鱼及其浮游猎物和捕食者的空间分布。它们的性质各不相同，它们可能使幼鱼在较小的时空尺度上暴露于不同的营养环境，对生存和募集产生未知的后果。在加利福尼亚北部的洋流中，哥伦比亚河的羽流受到每天两次的淡水注入的强烈影响，从而形成了高度动态的沿海环境。使用原位鱼类浮游生物成像系统，我们研究了幼体鱼，它们的猎物和它们的天敌在空间和时间（潮涨潮落）中细尺度水平和垂直分布的变化。总共对6095个鱼幼虫和约150万个捕食/捕食性浮游动物进行了成像和测量。羽状区域相对于海洋水提供了实质上更高的猎物浓度，并增强了幼鱼及其猎物之间的空间重叠。河羽作为捕食者避难所的功能尚不清楚。羽状区域的捕食者浓度也较高，但与幼体鱼类的重叠是分类群特异性的，并随潮汐变化。值得注意的是，浮游动物浓度高的区域并不一定在与营养相互作用有关的小尺度（垂直米，水平公里）上赋予高空间重叠。a是影响浮游动物与幼体鱼类空间重叠的最重要因素。在河羽附近，幼虫鱼在短时空尺度上经历了多种独特的猎物和捕食场，这可能以比以前认为的更精细的尺度促成可变的生长和死亡方式。