Beschreibung: The sea ice structure of the Arctic Ocean has changed measurably in the last decades. Sea ice decline and warming of the surface water layers may affect composition and diversity of protist communities living in the sea ice interface and the pelagic realm. Samples from different habitats were analyzed (1) to investigate the impact of sea ice on the protists and, (2) to elucidate cryo-pelagic coupling. Samples were collected from melt ponds, sea ice, under-ice water and water column during two RV Polarstern cruises to the Central Arctic Ocean in August - September 2011 & 2012. Automated ribosomal intergenic spacer analysis (ARISA) from 182 samples and Illumina-sequencing of 57 samples revealed a high heterogeneity between different melt pond and sea ice samples, whereas samples from the water column were more homogeneous. However, different sea ice habitats showed similar patterns in protist community structure at the same station, indicating intensive sea-ice-water-exchange during melting and freezing processes. These results illustrate that the high biodiversity in the Central Arctic is mainly governed by the sea ice origin compared to the oceanic currents.

Beschreibung: In the Arctic Ocean, sea-ice decline will significantly change the structure of biological communities. At the same time, changing nutrient dynamics can have similarly strong and potentially interacting effects. To investigate the response of the taxonomic and trophic structure of planktonic and ice-associated communities to varying sea-ice properties and nutrient concentrations, we analysed four different communities sampled in the Eurasian Basin in summer 2012: (1) protists and (2) metazoans from the under-ice habitat, and (3) protists and (4) metazoans from the epipelagic habitat. The taxonomic composition of protist communities was characterised with 18S meta-barcoding. The taxonomic composition of metazoan communities was determined based on morphology. The analysis of environmental parameters identified (i) a ‘shelf-influenced’ regime with melting sea ice, high-silicate concentrations and low NOx (nitrate + nitrite) concentrations; (ii) a ‘Polar’ regime with low silicate concentrations and low NOx concentrations; and (iii) an ‘Atlantic’ regime with low silicate concentrations and high NOx concentrations. Multivariate analyses of combined bio-environmental datasets showed that taxonomic community structure primarily responded to the variability of sea-ice properties and hydrography across all four communities. Trophic community structure, however, responded significantly to NOx concentrations. In three of the four communities, the most heterotrophic trophic group significantly dominated in the NOx-poor shelf-influenced and Polar regimes compared to the NOx-rich Atlantic regime. The more heterotrophic, NOx-poor regimes were associated with lower productivity and carbon export than the NOx-rich Atlantic regime. For modelling future Arctic ecosystems, it is important to consider that taxonomic diversity can respond to different drivers than trophic diversity.