Mixotrophic Protists in the Arctic - Alternative Nutritional Strategies

Rebecca Gast, Biology

Arctic Research Initiative
2008 Funded Project

Abstract

Protists are traditionally described as either phototrophic (function as plants) or heterotrophic (function as predators or grazers), and this defines how they contribute to the generation and use of nutrients and carbon within the microbial food web. As usual, nature is not so black and white, and there are actually groups of algae that can successfully do both, and they are called
mixotrophs. These organisms include species of chrysophytes, dinoflagellates, prymnesiophytes and cryptophytes, and in some environments they can comprise up to 50% of the photosynthetic population, and 75% of the heterotrophic population. Our recent work in the Ross Sea, Antarctica has indicated that mixotrophic protists comprise a significant percentage of the phagotrophic nanoplankton. This has led us to propose that mixotrophy is an alternative microbial dietary strategy of potentially importance in polar marine environments, facilitating survival in long periods of darkness. In this project, we will focus on determining whether, and to what extent, mixotrophic protists are present in the Arctic marine environment. Despite numerous studies on microbial communities in Arctic marine environments, none have addressed the issue of mixotrophy, although it is often mentioned. Experiments will also be run to establish rates of bacterivory for mixotrophs compared to strictly heterotrophic protists to help understand the potential impact of each trophic group. In addition, samples will be taken from each experiment to determine the genetic identities of the mixotrophic population for comparison with Southern Ocean samples.