Meeting Abstract
Despite the traditional view of protistan species as either phototrophic or heterotrophic, there are many photosynthetic protists that consume prey (mixotrophy). Some modeling studies suggest that mixotrophic activity will increase under warming scenarios and that they have the potential to dramatically alter the flow of nutrients in aquatic environments when compared with food webs dominated by strict autotrophs and heterotrophs. Mixotrophy is a widespread phenomenon in aquatic systems, but the factors known to induce this activity, including light limitation and micronutrient deficiencies, go through dramatic changes in the Southern Ocean. The contribution of mixotrophy is likely seasonal and linked to the taxonomic composition of the community. We have surveyed the presence and grazing impacts of mixotrophic phytoflagellates in Austral spring (2008), summer (2011) and late fall (2019). Our research indicates that these organisms can play a significant role as bacterivores in polar ecosystems, potentially consuming up to 100% of daily bacterial standing stock in the spring and comprising up to 75% of the grazing community in the summer. We have begun to use tracer studies of ingestion to identify unknown active mixotrophic species, quantification using qPCR, and transcriptome comparisons to better understand the taxonomic and functional diversities of the mixotrophic community.
