Data from: Fear dynamically structures the ocean's pelagic zone

Fear of predation can have wide-ranging ecological effects.This is especially true in the ocean's pelagic zone, the Earth's largest habitat, where vertical gradients in light and primary productivity force numerous taxa to migrate vertically each night to feed at the surface while minimizing risk from visual predators. Despite its importance, and the fact that it is driven by spatial differences in perceived risk, diel vertical migration (DVM) is rarely considered within the "landscape of fear" framework. It is also far from the only such process in the pelagic zone. We used continuous, year-long records from an upward-looking echosounder and broadband hydrophone at a cabled observatory off Central California, USA, to observe avoidance reactions by several groups of pelagic animals to the presence of their predators. As expected, vertical migration was ubiquitous, but we also observed behaviors at shorter and longer time-scales which were best explained by fear of predation. The presence of foraging odontocetes induced immediate diving behavior in mesopelagic sound-scattering layers, and schools of epipelagic fishes induced similar behaviors in layers of zooplankton and mesopelagic micronekton. At longer time scales, the presence of fish schools significantly deepened vertical migration, rearranging life throughout the water column. We argue that behavioral reactions to predation risk are common in the pelagic zone at a range of spatiotemporal scales and that our understanding of food webs and biogeochemical cycling in this immense biome will be incomplete unless we account for fear.

捕食恐惧可引发广泛的生态效应，这一点在地球最大的栖息地——海洋远洋带（pelagic zone）中尤为突出：该区域内光照与初级生产力的垂直梯度，迫使众多生物类群在夜间开展垂直迁移，前往表层水域觅食的同时，尽可能降低遭遇视觉捕食者的风险。尽管昼夜垂直迁移（diel vertical migration, DVM）至关重要，且其驱动机制为感知到的风险空间差异，但该过程极少被纳入"恐惧景观（landscape of fear）"研究框架；此外，这类捕食风险驱动的行为过程在远洋带中绝非仅有。我们依托美国加利福尼亚中部近海的缆式观测站，利用向上安装的回声测深仪与宽带水听器获取了一整年的连续观测数据，以此记录远洋带多个类群的动物对捕食者存在的回避行为。正如预期，垂直迁移现象普遍存在，但我们还观测到了时间尺度更短与更长的行为模式，这些行为最适宜用捕食恐惧来解释：觅食性齿鲸类（odontocetes）的出现，会触发中层深海声散射层（mesopelagic sound-scattering layers）的即时下潜行为；而表层洄游鱼类（epipelagic fishes）群的存在，则会使浮游动物与中层深海小型游泳生物（mesopelagic micronekton）所在的水层产生类似的下潜反应。在更长的时间尺度上，鱼类群的出现会显著加深垂直迁移的深度，进而重塑整个水柱中的生物分布格局。我们认为，对捕食风险的行为反应在远洋带的各类时空尺度上都普遍存在；若不考虑恐惧效应，我们对这一巨型生物群系的食物网与生物地球化学循环的认知将是不完整的。