Microbial Eukaryotes in an Arctic Under-Ice Spring Bloom North of Svalbard.

Microbial eukaryotes can play prominent roles in the Arctic marine ecosystem, but their diversity and variability is not well known in the ice-covered ecosystems. We determined the community composition of microbial eukaryotes in an Arctic under-ice spring bloom north of Svalbard using metabarcoding of DNA and RNA from the hypervariable V4 region of 18S nrDNA. At the two stations studied, the photosynthetic biomass was dominated by protists >3 µm and was concentrated in the upper 70-80 m, above the thermocline and halocline. Hierarchical cluster analyses as well as ordination analyses showed a distinct clustering of the microbial eukaryote communities according to a combination of water mass and local environmental characteristics. While samples collected in the surface mixed layer differed distinctly between the two sites, the deeper communities collected in Atlantic Water were fairly similar despite being geographically distant. The differentiation of the microbial eukaryote communities of the upper mixed water was probably driven by local development and advection, while the lack of such differentiation in the communities of Atlantic Water reflects the homogenizing effect of water currents on microbial communities.

Floating ice-algal aggregates below melting arctic sea ice.

During two consecutive cruises to the Eastern Central Arctic in late summer 2012, we observed floating algal aggregates in the melt-water layer below and between melting ice floes of first-year pack ice. The macroscopic (1-15 cm in diameter) aggregates had a mucous consistency and were dominated by typical ice-associated pennate diatoms embedded within the mucous matrix. Aggregates maintained buoyancy and accumulated just above a strong pycnocline that separated meltwater and seawater layers. We were able, for the first time, to obtain quantitative abundance and biomass estimates of these aggregates. Although their biomass and production on a square metre basis was small compared to ice-algal blooms, the floating ice-algal aggregates supported high levels of biological activity on the scale of the individual aggregate. In addition they constituted a food source for the ice-associated fauna as revealed by pigments indicative of zooplankton grazing, high abundance of naked ciliates, and ice amphipods associated with them. During the Arctic melt season, these floating aggregates likely play an important ecological role in an otherwise impoverished near-surface sea ice environment. Our findings provide important observations and measurements of a unique aggregate-based habitat during the 2012 record sea ice minimum year.

MOLECULAR CHARACTERIZATION AND ANTIBODY DETECTION OF A NITROGEN-REGULATED CELL-SURFACE PROTEIN OF THE COCCOLITHOPHORE EMILIANIA HUXLEYI (PRYMNESIOPHYCEAE)(1).

Dissolved organic nitrogen (DON) can account for a significant portion of total nitrogen in some aquatic environments, and many species of phytoplankton are able to scavenge nitrogen from this pool especially when inorganic nitrogen is limiting. Emiliania huxleyi (Lohmann) H. W. Hay et H. Mohler is able to use various forms of DON for growth, including several amino acids, purines, and pyrimidines. A cell-surface protein up-regulated in the absence of inorganic nitrogen, NRP1, is hypothesized to play a role in the metabolism of one or more of these organic nitrogen forms. Here, the genomic and cDNA sequence of NRP1 is reported. Structural predictions based on the amino acid sequence suggest a pyridoxal-5'-phosphate-dependent enzyme that may have a role in acquiring nitrogen from amino acids. Further evidence for the function of NRP1 is measured in spent media from nitrogen-limited cultures, which contain NRP1 and have glutaminase and formamidase activity. Field studies using an antibody to NRP1 show that it is expressed in E. huxleyi during bloom conditions in a Norwegian fjord.