Vertical Migration of Pelagic Tunicates: Role of Feeding and Reproduction

本研究的重点是在百慕达大西洋时间序列站附近的海鞘垂直迁移。海带是浮游植物和其他微粒的高效食草动物；它们分布广泛，有时出现在密集的种群中。一些物种垂直迁移，一些最远可达800米，而另一些则局限于地表水。最近在亚北极太平洋和百慕大附近的研究揭示了这些迁徙的有趣的新特征，这些特征似乎与迁徙优势的传统理论不一致。太平洋上的海鞘进行浅层迁徙，但在夜间在海面上停止进食。这种行为被认为主要与产卵和受精有关。最近，人们观察到海鞘总是在一天的不同时间出现在海面上——早上、下午和晚上。这种明显的迁移也与通常的解释不一致。珀塞尔博士和他的合作者将调查这一极其重要的远洋食草动物群体的行为。他们将测试观察到的迁徙模式的两个非排他性假设：1)迁徙优化了食物丰富的深度，或者在空间上共同发生的物种之间暂时分配食物；2)洄游使海鞘集中在海面，并同步产卵和受精。研究主要涉及浮游动物迁徙的适应和生态学、海鞘的生殖生理、竞争和生态位分离等基本问题。它们对于计算海鞘的放牧和迁移对颗粒和溶解营养物垂直通量的作用也至关重要。

This investigation focuses on diel vertical migration by salps (pelagic tunicates) in the vicinity of the Bermuda Atlantic Time Series Station. Salps are efficient grazers on phytoplankton and other particulates; they are widely distributed and sometimes occur in dense populations. Several species migrate vertically, some as far as 800 m, while others are restricted to surface waters. Recent work in the Subarctic Pacific and near Bermuda has revealed intriguing new features to these migrations, which do not seem consistent with traditional theories for the advantages of migration. Salps in the Pacific make shallow migrations, but stop feeding while at the surface during the night. This behavior is believed to relate mainly to spawning and fertilization. Recently salps have been observed to consistently appeared at the surface at different times of day - morning, afternoon and night. This apparent migration is also inconsistent with the usual explanations. Dr. Purcell and collaborators will investigate the behavior of this extremely important group of pelagic herbivores. They will test two, non-exclusive hypotheses for the migratory patterns observed: 1) migration optimizes feeding at food-rich depths, or temporally partitions food among spatially co- occurring species; 2) migration concentrates salps at the surface and synchronizes spawning and fertilization. The investigations address basic questions of adaptation and ecology in migrating zooplankton, reproductive physiology of salps, and competition and niche separation. They are also critical for calculations of the role of grazing and migration by salps on vertical fluxes of particulate and dissolved nutrients.