Response of bacterial communities from Kongsfjorden (Svalbard, Arctic Ocean) to macroalgal polysaccharide amendments.

Macroalgae are abundant in coastal Arctic habitats and contain a large amount of polysaccharides. Increased macroalgal productivity due to warmer temperatures and reduced sea-ice cover contribute a significant amount of polysaccharide-rich detritus in the region. To study bacterial degradation of macroalgal polysaccharides and their potential impact on biogeochemical processes we studied the response of bacterial communities from Kongsfjorden, Svalbard (Arctic Ocean) to alginate (AL) and agarose (AG) amendments, using an ex-situ microcosm experiment. Our results show that bacterial communities responded to the increased availability of macroalgal polysaccharides and community shift was congruent with a significant decline in nutrient concentrations. Initially-rare bacterial taxa affiliated with Gammaproteobacteria and Bacteroidia responded to the polysaccharide addition. Each polysaccharide addition incited the growth of certain distinct bacteria taxa. Compared to the un-amended control microcosms (CM), Polaribacter, Colwellia, Pseudoalteromonas, and unclassified Gammaproteobacteria responded to AL addition, whereas Paraglaciecola, Lentimonas, Colwellia, unclassified Gammaproteobacteria, unclassified Alteromonadales, and unclassified Alteromonadaceae responded to the AG addition. These results suggest that polysaccharides shift bacterial community composition towards copiotrophic bacterial taxa, with implications for carbon and nutrient cycling in coastal Svalbard.