Dave Caron and Darcy Lonsdale; Woods Hole Oceanographic Institution and SUNY-Stony Brook

U.S. JGOFS: Seasonal contribution of nano- and microzooplankton to Antarctic food web structure

Our overall goal is to examine microbial bacterivory and herbivory over an annual cycle in the Ross Sea. In order to accomplish that task, we will make measurements of microbial standing stocks and rates of growth and grazing by microbial assemblages. We will also examine the importance of mixotrophic behavior (combined phototrophic and heterotrophic nutrition) as a strategy for survival among Antarctic protists. JGOFS 'core' measurements that we will make will include abundances and biomasses of phototrophic and heterotrophic nanoplankton (algae and protozoa 220 Fm in size), and abundances and biomasses of phototrophic and heterotrophic microplankton (algae and protozoa 20200 Fm in size). These standing stock measurements will complement the bacterial and meso/macrozooplankton work being conducted by other PIs. We expect (not knowing exact cruise plans) to characterize vertical distributions of these assemblages at 1216 stations. Microbial herbivory (also a JGOFS core measurement) and bacterivory will be measured by dilution technique at 68 stations (we'll also use a backup technique for bacterivory in the event that rates are exceedingly low). Growth of selected heterotrophic protistan assemblages will be determined by populations increases in size fractionated water samples. We will assay for abundances of mixotrophic phytoflagellates and ciliates at each of the stations at which we measure herbivory and bacterivory using fluorescently labeled particles to identify mixotrophic phytoflagellates (by particle ingestion) and using direct epifluorescence microscopy to determine mixotrophic ciliates.