A Comprehensive Evaluation of Herbivory by in Situ Assemblages of Pelagic Protists

目前生物海洋学中最紧迫的问题之一就是小型光养生物在远洋食物网中的命运。基于理论考虑以及实验室和现场数据，普遍的概念是，食性原生生物是5微米大小细胞的主要捕食者，也可能消耗较大浮游植物生物量的很大一部分。以前对原生食草动物的大多数研究要么涉及单一物种(主要是纤毛虫)的实验室实验，要么涉及对自然浮游植物组合的总微型浮游动物捕食压力的估计。需要更全面地了解这一环节在中上层食物网中的组成部分的大小和细节，特别是在吞噬鞭毛虫的作用方面。谢尔博士和他的合作者将在俄勒冈州沿海水域的天然浮游群落中研究浮游鞭毛虫和纤毛虫的食草性。将讨论的问题包括：1)捕食性原生动物对5微米大小的浮游植物的捕食影响是否大于5微米大小的浮游植物？2)鞭毛虫和纤毛虫对浮游植物的相对放牧影响是什么？3)原生食草动物的比率是否表现出一致的昼夜差异？4)捕食密度的阈值是否存在？5)捕食是否影响浮游植物的细胞分裂率？6)吞食性原生生物在不同的浮游植物类群中是否表现出选择性取食？

One of the most urgent questions in biological oceanography at present is that of the fate of small phototrophs in pelagic food webs. The prevailing concept, based on both theoretical considerations as well as laboratory and field data, is that phagotrophic protists are the dominant predators of 5 um sized cells, and as well may consume a significant portion of the biomass production of larger phytoplankton. Most previous studies of protistan herbivory have involved either laboratory experiments with single species, primarily ciliates, or estimation of total microzooplankton grazing pressure on natural phytoplankton assemblages. A more complete picture of the magnitude and details of the component parts of this link in pelagic food webs in needed, especially with respect to the role of phagotrophic flagellates. Dr. Sherr and collaborators will investigate herbivory by pelagic flagellates and ciliates in the natural planktonic assemblages of Oregon coastal waters. Questions addressed will include: 1) Do phagotrophic protists have a greater grazing impact on 5 um sized phytoplankton than on cells 5 um? 2) What is the relative grazing impact of flagellates versus ciliates on phytoplankton? 3) Do rates of protistan herbivory show consistent day/night differences? 4) Do thresholds of prey density exist? 5) Does predation affect the cell division rates of phytoplankton? 6) Do phagotrophic protists show selective feeding among various phytoplankton taxa in situ?