Zooplankton Behavioral Response to Planktivorous Fish

华盛顿州杰克尔斯湖存在一个简单但自然的海洋中上层捕食-被捕食系统，为研究鱼类捕食对浮游动物行为的影响提供了理想的实验模型。这个模型捕食者-食饵系统将被用来通过直接实验来检验这样的假设，即浮游动物的垂直迁移是躲避捕食者的一种策略。这将通过在围栏中操纵浮游桡足类动物Acartia hudsonica及其天敌--食浮性鱼类Gastersteus aculeatus的种群来实现。实验和补充的野外观察将建立由鱼类捕食在桡足类种群中诱导迁徙行为的条件，并确定诱导的具体机制。这是对捕食假说的第一次实验检验，其结果将具有广泛的意义，不仅对于理解湖泊和海洋中上层水生生物的垂直迁移行为，而且对于解决水生中上层生态学中捕食者-猎物相互作用的更一般方面，如被捕食者利用避难所，将具有广泛的意义。%由于许多原因，包括难以获得复制样本、捕食者和猎物在剪切循环中的不同运动以及所占“活体积”的不匹配(比例不匹配)，对涉及中上层系统脊椎动物的捕食者-猎物相互作用知之甚少。如果捕食者被限制在一个可以从猎物的角度进行研究的体积，那么这个体积通常非常小，以至于捕食者的行为发生了实质性的变化。对于捕食者来说，足够大的体积不能为猎物提供足够的样本。然而，在杰克斯泻湖，浮游群落的多样性很低，随着捕食者浓度的增加和减少，猎物的行为发生了变化。多年来，人们一直认为，在远洋海洋系统中，甲壳类猎物的垂直迁徙是对肉眼搜索捕食者的反应。这项研究将对这一假设进行定量检验。

A simple, but natural, marine pelagic predator-prey system affording an ideal model for experimental investigation of the effect of fish predation on zooplankton behavior exists in Jackles Lagoon in the state of Washington. This model predator- prey system will be used to test, by direct experimentation, the hypothesis that diel vertical migration by zooplankton is a tactic for evading predators. This will be done by manipulation of populations of a planktonic copepod, Acartia hudsonica, and its natural predator, the planktivorous fish Gasterosteus aculeatus, in enclosures. Experiments and supplemental field observations will establish the conditions under which migration behavior is induced in the copepod population by fish predation, and to identify the specific mechanisms of induction. This is the first experimental test of the predation hypothesis and the results will have wide implications, not only for understanding diel vertical migration behavior of pelagic oarganisms in lakes and seas, but also for addressing more general aspects of predator-prey interactions, such as refuge use by prey, in aquatic pelagic ecology. %%% Predator-prey interactions involving vertebrates in pelagic systems are poorly understood for many reasons including the difficulty in obtaining replicate samples, differential movements of predators and prey in sheared circulation, and mismatches in the "living volume" occupied (scale mismatch). If the predators are confined to a volume that can be studied from the point of view of prey, the volume is generally so small that behavior of the predator is substantially altered. A volume large enough to be realistic for the predator cannot be sampled adequately for prey. In Jackles Lagoon, however, the planktonic community is low in diversity, and alteration of behavior on the part of prey has been noted in response to increasing and decreasing concentrations of predators. For many years it has been suggested that diel vertical migration by crustacean prey in pelagic marine systems is a response to visually searching predators. This study will quantitatively test that supposition.