Bacterial colonization of gel particles in the sea ice of Fram Strait

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The Fram Strait is characterized by seasonal ice cover, influenced by cold Arctic waters flowing southward on the western margin and warm Atlantic waters flowing northward on the eastern margin. A key component of sea ice ecology is the organic particles and their bacterial communities, about which little is known. We investigated the within-ice distribution of transparent exopolymeric particles (TEP, primarily polysaccharide) and Coomassie stainable particles (CSP, primarily protein) as well as parameters affecting their respective abundance within sea ice. We then explored differences in the bacterial community composition associated with TEP and CSP, compared to free-living bacteria in early summer sea ice of Fram Strait. Photometric and microscopic analysis of gel particles indicated highest TEP and CSP values in landfast ice and lowest values in small ice floes floating on cold Arctic and warm Atlantic waters, respectively (only significant for CSP). TEP were generally found in the bottom half of sea ice, dominating in terms of particle number and area, whereas CSP were evenly distributed, dominating in the top half of sea ice in terms of particle area. TEP values were significantly correlated with indices of recent productivity such as chlorophyll a, POC and PON concentrations. CSP values were less obviously dependent on the productivity of the system. Instead, CSP seemed driven more by low temperature and low light, possibly conditions negatively affecting the survival of sea ice microorganisms generally. Fluorescence in-situ hybridization and particle-specific staining methods were combined to investigate the bacterial community directly living attached to either TEP or CSP. The composition of particle-associated bacteria was different from that of free-living bacteria, but was dominated by the same bacterial groups, Bacteroidetes and ɣ-proteobacteria. Polaribacter spp. was the only genus significantly reduced on particles. We found minor preferences of some bacterial groups for either TEP or CSP, none of which was significant.Distribution patterns and drivers of TEP and CSP suggest different roles of these particles in sea ice. Since no complete shifts in bacterial community composition were observed, we conclude that sea ice selects for bacteria able to acclimate rapidly to changing conditions.

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Dietrich, U. (2015): Bacterial colonization of gel particles in the sea ice of Fram Strait , Master thesis, Alfred Wegener Institute for Polar and Marine Research.

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