Vertical Migration of Pelagic Tunicates: Role of Feeding and Reproduction

本次调查的重点是百慕大大西洋时间序列站附近的盐藻(中上层衣藻)的海底垂直迁移。盐碱是浮游植物和其他颗粒的有效捕食者；它们分布广泛，有时出现在密度较高的种群中。一些物种垂直迁徙，有些迁徙到800米远，而另一些物种则局限于地表水。最近在次北冰洋和百慕大附近进行的研究揭示了这些迁徙的耐人寻味的新特征，这似乎与关于迁徙优势的传统理论不一致。太平洋的盐碱地进行浅层迁徙，但夜间在海面时停止觅食。这种行为被认为主要与产卵和受精有关。最近，人们观察到盐渍在白天的不同时间--上午、下午和晚上一直出现在海面上。这种明显的迁移也与通常的解释不一致。米勒博士和他的合作者将研究这一极其重要的远洋食草动物群体的行为。他们将检验观察到的迁徙模式的两个非排他性假设：1)迁徙在食物丰富的深处优化觅食，或将食物暂时分配给空间上共存的物种；2)迁徙使盐分集中在表面，并同步产卵和受精。这些调查涉及迁徙浮游动物的适应和生态学、盐生植物的生殖生理以及竞争和生态位分离等基本问题。它们对于计算盐分放牧和迁移对颗粒和溶解营养物质垂直通量的作用也是至关重要的。

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. Miller 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.