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是远洋食物网中小型光养生物的命运。基于理论考虑以及实验室和现场数据，流行的概念是，吞噬性原生生物是5um大小细胞的主要捕食者，并且可能消耗较大浮游植物生物量的很大一部分。以前对原生动物食草性的大多数研究要么涉及单个物种（主要是纤毛虫）的实验室实验，要么涉及对天然浮游植物组合的总浮游微动物放牧压力的估计。需要更全面地了解这一环节在远洋食物网中组成部分的规模和细节，特别是关于吞噬性鞭毛虫的作用。Sherr博士和合作者将研究俄勒冈州沿海水域天然浮游生物群落中上层鞭毛虫和纤毛虫的食草性。讨论的问题将包括：1)吞噬原生生物对5um大小的浮游植物的放牧影响是否大于对5um大小的细胞的放牧影响？2)鞭毛虫和纤毛虫对浮游植物的相对放牧影响是什么？3)草食原菌率是否表现出一致的昼夜差异？4)猎物密度是否存在阈值？5)捕食是否影响浮游植物的细胞分裂率？6)在不同的浮游植物分类群中，吞噬原生生物是否表现出选择性摄食？

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?