Algivorous Cercozoa shape the community composition of cryptogamic covers, the dominant vegetation in Polar Regions.

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Predator-prey dynamics of prokaryotes and their eukaryotic consumers have long been in focus of microbial ecology, but microbial eukaryote-eukaryote interactions were less investigated. Microalgae play the key role as primary producers in marine and freshwater ecosystems of Antarctica and almost all energy and nutrients are channelled here via algae to higher trophic levels. In contrast and in this context, terrestrial ecosystems of Antarctica are unstudied. Terrestrial vegetation is usually dominated by vascular plants as primary producers, but the terrestrial vegetation of Antarctica is dominated by cryptogamic covers (like biocrusts), and the abundant terrestrial algae within. Up to 55% of the vegetated land surface on the Antarctic Peninsula and 70% of the vegetated land surface on Arctic Svalbard is covered by biological soil crusts (biocrusts); these numbers can be expected to increase considering a predicted warming of the Polar Regions (e.g. “Arctic Greening”) due to climate change. A significant proportion of polar primary production can thus be expected to be conducted by biocrust algae at high latitudes. Nevertheless, it is unexplored how this energy is channelled to higher trophic levels, especially when considering the scarcity of algivorous metazoans in Antarctica. Cercozoa are one of the most abundant unicellular eukaryotes (protists) in terrestrial habitats, and as preliminary results show: Algivorous Cercozoa dominate biocrusts in Polar Regions. We will illuminate for the first time predator-prey relationships in biocrusts between algae as main primary producers and the most important algivores to complement the soil microbial food web in both Polar Regions. For this we will combine barcoded-primer based high through-put Illumina surveys coupled with trait-based data analyses and complemented with traditional culture-based experiments to obtain a comprehensive picture based on predator-prey relations of microalgae and Cercozoa, thereby addressing for the first time their structure and function in terrestrial ecosystems of Antarctica and the Arctic. Such data will contribute to the questions how relevant the soil microbial food-web is in the Polar Regions and whether global warming has the potential to change these interactions?