INVESTIGATING SOUTHERN OCEAN MIXOTROPHIC BACTERIVORY RATES UNDER IRON AND MANGANESE LIMITATION

Mixotrophs have the capacity to utilize phototrophic and phagotrophic trophic modes, with their behavior dependent on conditions such as nutrient concentrations, prey availability, and physiochemistry. Historically, mixotrophic research has focused on quantifying how their ingestion rates vary as a function of macronutrients and irradiance levels. However, in the Southern Ocean, iron (Fe) and manganese (Mn) concentration are low enough to inhibit photosynthetic growth and may stimulate bacterivory in mixotrophs. To explicitly test this, we measured the ingestion rate of three cultures of Southern Ocean mixotrophs, Mantoniella antarctica (prasinophyte), Geminigera cryophile (cryptophyte), and Pyramimonas tychotreta (prasinophyte), on bacteria under a matrix of Fe/Mn conditions. Ingestion rates on bacteria were measured using a modified version of prey removal experiments where the growth rates of bacteria were tracked over 24-hours when grown alone and in the presence of mixotrophs. The results to be presented represent a first attempt to investigate mixotrophs grazing response under Mn and Fe limitation. Preferentially relying upon grazing during low micronutrient conditions would allow Antarctic mixotrophs to persist, and perhaps thrive, at certain times of the year compared to strict phototrophs that are dependent on external dissolved metals for growth. These findings will be valuable in understanding plankton food web dynamics in a changing Antarctic climate, which likely includes shifts in Fe and Mn bioavailability to phytoplankton.

Presentation Preference: Oral

Primary Presenter: Nicole Millette, Virginia Institute of Marine Science (nmillette@vims.edu)

Authors:

Claire Cook, Department of Marine Sciences, Skidaway Institute of Oceanography, University of Georgia  (claire.czc@uga.edu)

Heather Corson, Coastal and Ocean Processes, Virginia Institute of Marine Science, William & Mary  (hkcorson@vims.edu)

Natalie Cohen, Department of Marine Sciences, Skidaway Institute of Oceanography, University of Georgia  (cohen@uga.edu)