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We investigated marine picoeukaryotic diversity (cells <3 µm) in samples collected in late summer 2002 at the boundary between the Norwegian, Greenland, and Barents Seas. The two main Arctic and Atlantic water masses in this region are separated by the polar front. We combined total counts of picoeukaryotes assemblages by flow cytometry and epifluorescence microscopy with taxa detection by tyramide signal amplification-fluorescent in situ hybridization (TSA-FISH) and high performance liquid chromatography (HPLC) pigment analyses. The picoeukaryotic community was primarily composed of photoautotrophs (75% of the cells on average). Members of the division Chlorophyta, in particular the species Micromonas pusilla (Butcher) Manton and Parke, were the major components in truly Arctic waters (32% of the picoeukaryotes, maximum 3,200 cells ml-1). M. pusilla was also well represented in coastal waters and at the polar front (25% of the picoeukaryotes, maximum 9,100 cells ml-1). Haptophyta were prominent in more typical Atlantic waters (up to 35% of the picoeukaryotes, maximum 4,500 cells ml-1). Quantification of haptophyte biomass by HPLC pigment analyses and CHEMTAX, and haptophyte abundances by TSA-FISH were in good agreement. This confirms previous studies, which suggested that M. pusilla is a dominant contributor of picoeukaryotic communities in both coastal and nutrient rich environments, whereas haptophytes seem to be more important in open seawaters. [ABSTRACT FROM AUTHOR]

We used a molecular fingerprinting technique to analyze the distribution and composition of eukaryotic picoplankton along latitudinal transects in the Southern Ocean. First, primers specific for eukaryotic 18S rDNA were used in a polymerase chain reaction (PCR) with environmental DNA. The amplification products were subjected to denaturing gradient gel electrophoresis (DGGE). Transect DOVETAIL (44°W) went from the ice edge (at 60°S) across the Weddell-Scotia confluence and north to 58°S; it was sampled in January 1998 (summer). Transect DHARMA (between 53°W and 58°W) went from the ice edge in the Weddell Sea (63°S) across the Drake Passage to the South American continental platform (55°S); it was sampled in December 1998 (late spring). DGGE band patterns were used to build dendrograms combining samples from each cruise. Samples were grouped in several distinct clusters that were generally consistent with the hydrography of the area. In DOVETAIL, the upper water column was stratified and the DGGE band patterns varied with depth. In DHARMA the upper mixed layer showed the same composition of the eukaryotic picoplankton at all depths. The most dominant DGGE bands were excised and sequenced. Some were closely related to well-known components of the plankton such as prasinophytes, prymnesiophytes, dinoflagellates, and diatoms. A significant number of sequences were related to previously unknown phylogenetic groups, including novel stramenopiles and alveolates or to poorly known groups such as cercomonads. This fingerprinting technique is useful for a rapid evaluation of the spatial distribution of picoeukaryotic assemblages in the oceans. [ABSTRACT FROM AUTHOR]

Bacterivory was determined in surface waters of Franklin Bay, western Arctic, over a seasonal ice-covered period (winter-spring, 2003-2004). The objectives were to obtain information on the functioning of the microbial food web under the ice, during winter (from 21 December 2003 to 21 March 2004) and during spring (from 22 March 2004 to 29 May 2004), and to test whether bacterial losses would increase after the increase in bacterial production following the spring phytoplankton bloom. Chl a concentrations ranged from 0.04 to 0.36 µg L-1, increasing in March and reaching a peak in April. Bacterial biomass showed no consistent trend for the whole period, and protist biomass followed a pattern similar to that of Chl a. Bacterial production increased 1 week after Chl a concentrations started to increase, while bacterivory rates increased very slightly. Average bacterivory rates in winter (0.16 ± 0.07 µg C L-1 d-1) were not significantly different from those in spring (0.29 ± 0.24 µg C L-1 d-1). Average bacterial production, on the other hand, was similar to bacterivory rates in winter (0.19 ± 0.38 µg C L-1 d-1), but higher than bacterivory in spring (0.93 ± 0.28 µg C L-1 d-1). Therefore, bacterial production was controlled by grazers during winter and by substrate concentration in spring. [ABSTRACT FROM AUTHOR]

We examined the potential response of Southern Ocean pelagic ecosystems to warming through changes in total primary production (particulate plus dissolved = PPP + DPP) and bacterial production (BP), determined simultaneously at ambient temperature (-1.4 to 0.4°C) and at 2°C in eight experiments performed near the Antarctic Peninsula in late spring 2002. Short (<6 h) time course experiments of radiocarbon uptake and photosynthesis-irradiance relationships consistently showed that a significant amount of photosynthate appeared as dissolved substances, with a mean 35% extracellular release (PER). Whereas PPP remained virtually unchanged (0.7 mg C m-3 h-1), DPP increased significantly at 2°C from 0.5 to 0.9 mg C m-3 h-1. The corresponding increase in PER (54% on average) was significantly and positively correlated with the temperature difference among treatments, suggesting that an increase in DPP could be expected with a temperature rise in the Southern Ocean. BP, estimated via [3H]leucine incorporation, tended to increase at 2°C only at low absolute values, and this increment was inversely related to PPP. However, our results show that the estimated bacterial carbon demand (BCD) was generally well below concurrent DPP at both treatments (mean BCD:DPP ratios of 0.60 and 0.27 at ambient temperature and 2°C, respectively), indicating that temperature-related extra inputs of organic substrates were not fully and immediately processed by bacteria. To the extent that these results reflect general ecophysiological trends, warming of Southern Ocean surface waters could produce changes in plankton-mediated biogeochemical processes leading to a greater importance of dissolved organic matter fluxes. [ABSTRACT FROM AUTHOR]