Beltran Roxanne S, Kilpatrick A Marm, Breed Greg A, Adachi Taiki, Takahashi Akinori, Naito Yasuhiko, Robinson Patrick W, Smith Walker O, Kirkham Amy L, Burns Jennifer M
Department of Biology and Wildlife, University of Alaska Fairbanks, 2090 Koyukuk Drive, Fairbanks, AK 99775, USA.
Department of Biological Sciences, University of Alaska Anchorage, 3101 Science Circle, Anchorage, AK 99508, USA.
Proc Biol Sci. 2021 Mar 31;288(1947):20202817. doi: 10.1098/rspb.2020.2817. Epub 2021 Mar 17.
Seasonal resource pulses can have enormous impacts on species interactions. In marine ecosystems, air-breathing predators often drive their prey to deeper waters. However, it is unclear how ephemeral resource pulses such as near-surface phytoplankton blooms alter the vertical trade-off between predation avoidance and resource availability in consumers, and how these changes cascade to the diving behaviour of top predators. We integrated data on Weddell seal diving behaviour, diet stable isotopes, feeding success and mass gain to examine shifts in vertical foraging throughout ice break-out and the resulting phytoplankton bloom each year. We also tested hypotheses about the likely location of phytoplankton bloom origination (advected or produced where seals foraged) based on sea ice break-out phenology and advection rates from several locations within 150 km of the seal colony. In early summer, seals foraged at deeper depths resulting in lower feeding rates and mass gain. As sea ice extent decreased throughout the summer, seals foraged at shallower depths and benefited from more efficient energy intake. Changes in diving depth were not due to seasonal shifts in seal diets or horizontal space use and instead may reflect a change in the vertical distribution of prey. Correspondence between the timing of seal shallowing and the resource pulse was variable from year to year and could not be readily explained by our existing understanding of the ocean and ice dynamics. Phytoplankton advection occurred faster than ice break-out, and seal dive shallowing occurred substantially earlier than local break-out. While there remains much to be learned about the marine ecosystem, it appears that an increase in prey abundance and accessibility via shallower distributions during the resource pulse could synchronize life-history phenology across trophic levels in this high-latitude ecosystem.
季节性资源脉冲会对物种间的相互作用产生巨大影响。在海洋生态系统中，用肺呼吸的捕食者常常会将其猎物驱赶到更深的水域。然而，尚不清楚诸如近表层浮游植物大量繁殖这样的短暂资源脉冲如何改变消费者在躲避捕食与资源可得性之间的垂直权衡，以及这些变化如何级联影响顶级捕食者的潜水行为。我们整合了威德尔海豹潜水行为、饮食稳定同位素、捕食成功率和体重增加的数据，以研究每年破冰期及随之而来的浮游植物大量繁殖期间垂直觅食行为的变化。我们还基于海冰破冰物候以及海豹栖息地150公里范围内多个地点的平流速率，对浮游植物大量繁殖起源的可能位置（平流而来或在海豹觅食处产生）的假设进行了检验。在初夏，海豹在更深的深度觅食，导致捕食率和体重增加较低。随着整个夏季海冰范围的缩小，海豹在较浅的深度觅食，并受益于更高效的能量摄入。潜水深度的变化并非由于海豹饮食或水平空间利用的季节性变化，相反，可能反映了猎物垂直分布的变化。海豹潜水变浅的时间与资源脉冲之间的对应关系每年都有所不同，并且无法通过我们现有的海洋和冰动力学知识轻易解释。浮游植物平流的发生速度比破冰快，而且海豹潜水变浅的时间比当地破冰时间早得多。虽然关于海洋生态系统仍有许多有待了解的地方，但在资源脉冲期间，猎物通过较浅分布而增加的丰度和可及性似乎可以使这个高纬度生态系统中各营养级的生活史物候同步。
