9634241 Lonsdale This research project is part of the US Joint Global Ocean Flux Study (JGOFS) Southern Ocean Program aimed at (1) a better understanding of the fluxes of carbon, both organic and inorganic, in the Southern Ocean, (2) identifying the physical, ecological and biogeochemical factors and processes which regulate the magnitude and variability of these fluxes, and (3) placing these fluxes into the context of the contemporary global carbon cycle. A major role for nanoplankton (2-20 um) and microplanktonic (20- 200 um) protozoa in pelagic food webs of the world ocean has been firmly established in recent years. Neritic and coastal ocean ecosystems have been extensively studied in this regard, and considerable information is also accumulating on the microbial processes of tropical and temperate oceanic ecosystems. In contrast, the role of nano-and microzooplankton in the flow of energy and elements through polar communities is less clear because of the difficulties associated with sampling and working in these environments, and because of the prevailing dogma that microbial processes may be overshadowed by `classical' phytoplankton-zooplankton-fish food webs in these environments. Clearly, there is now a great deal of information that is contradictory to this dogma, and numerous studies in recent years have documented an abundant and active protozoan fauna in polar ecosystems. Nevertheless, there are still substantial gaps in our understanding of the overall importance of the microbial loop in polar environments. This research project will examine questions concerning the ecological role of nano- and microplanktonic protozoa in the water column of the Ross Sea: (1) Do nano- and microplanktonic protozoa constitute a significant fraction of the zooplankton community in the Ross Sea? (2) Are these protozoa responsible for maintaining low phytoplankton and bacterial standing stocks in this environment? (3) Is mixotrophy (i.e., combined phototrophic and phagotrophic nutrition) an important adaptive behavior for the survival of protists in this planktonic Antarctic ecosystem? Studies will be conducted over an annual cycle in the Ross Sea in order to examine the expected strong seasonal variability in these features of protistan ecology. These studies constitute both "core" JGOFS measurements and supplementary studies designed to establish the seasonal contribution of protozoan biomass and grazing activity to the overall structure of the pelagic food web of the Ross Sea.
