| Summary: | Protists form a major part of the Arctic ecosystem and are of great importance for biodiversity and productivity of the Central Arctic Ocean (CAO). The sea ice is considered as one of the main factors that influence protist communities. Current changes in sea ice conditions are assumed to alter protist community biodiversity and composition in ice-influenced habitats with further implications for the overall productivity of the CAO and carbon sequestration to the deep sea. Protist taxa that are adapted to habitat-specific environmental conditions or available food sources might be affected most by the recent sea ice retreat. However, little is known about how drastic sea ice loss might affect biodiversity and composition of sea ice biota and phytoplankton. So far, in-depth knowledge about protist community structure and protist ecology in variable habitats of the CAO is still scarce and mainly based on the analysis of conventional approaches (e.g. light microscopy). Therefore, this thesis analyzed 18S amplicon sequence data in a total of 97 samples collected from the deep-chlorophyll maximum water depth, under-ice water, sea ice and melt pond water. Samples were collected in the CAO during August and September in 2011 and 2012 to investigate the environmental factors driving protist community structure and the potential consequences of sea ice retreat on protists in the CAO. The following questions will be addressed: 1. What are the influences of different sequence processing procedures on the resulting diversity and composition of protists obtained from environmental samples? 2. How does sea ice retreat and sea ice origin impact protist communities in the sea ice and water column of the CAO? 3. How habitat-specific are Arctic protist communities and is there any protist exchange between sea ice-influenced habitats in the CAO?
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