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. Shapiro 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?
