Springtime dynamics, productivity and activity of prokaryotes in two Arctic fjords
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In the Kongsfjorden–Krossfjorden system (Spitsbergen), increasing temperatures enhance glacier melting and concomitant intrusion of freshwater. These altered conditions affect the timing, intensity, and composition of the phytoplankton spring bloom in Kongsfjorden; yet, the effects on prokaryotes (bacteria and archaea) are not well understood. The aim of this study was to examine springtime prokaryote communities in both fjords as a function of hydrographic and phytoplankton variability. Prokaryote community composition was studied in two consecutive years by molecular fingerprinting of the 16S rRNA gene. In addition, we measured bacterial abundance, productivity (3H-Leucine uptake), and single-cell activity using catalyzed reporter deposition fluorescence in situ hybridization combined with microautoradiography. Differences in bacterial and archaeal communities were found between Kongsfjorden and Krossfjorden. Furthermore, an increase in productivity, abundance, and proportion of active bacterial cells was observed during the course of spring. Bacteroidetes were the most abundant bacterial group among the assessed taxa in both Kongsfjorden and Krossfjorden. Multivariate analysis of the microbial community fingerprints revealed a strong temporal shaping of both the bacterial and archaeal communities in addition to a spatial separation between the two fjords. A significant part of the observed bacterial variation could be explained by cyanobacterial biomass, as deduced from pigment analysis, and by phosphate concentration. Archaea were mainly controlled by abiotic factors. We speculate that the bacterial response to hydrographic changes and glacier meltwater is mediated through shifts in phytoplankton abundance and composition, whereas archaea are directly influenced by abiotic environmental variables.
KeywordsPolar Spitsbergen Bacteria Archaea Glacier melting Spring bloom Bacterial production Micro-CARD-FISH
This research was financed by NWO, as part of the IPY–PAME framework. Fieldwork at Koldeway station was supported and financed by the AWI. We thank A. K. Olstad, captain of the RV Teisten, and E. Austerheim, Kings Bay laboratory manager, for the wonderful collaboration. We are grateful to R. J. W. Visser for collecting the 2007 samples and running phytoplankton pigment analyses. Nutrients were analyzed at the NIOZ by J. van Ooijen. We also acknowledge Michael Greenacre (Universitat Pompeu Fabra, Barcelona, Spain) for his valuable help with the ordination and statistical analysis. We also like to thank the anonymous referees for their valuable suggestions and improvements.
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