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  • 1
    Electronic Resource
    Electronic Resource
    Bacterioplankton production in freshwater Antarctic lakes (2004)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 49 (2004), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Bacterioplankton production was measured in the water columns of two ultra-oligotrophic, freshwater Antarctic lakes (Crooked Lake and Lake Druzhby) during an annual cycle. In both lakes bacterial production, measured by the incorporation of [3H] thymidine, continued in winter and showed a cycle over the year. The range of production was between 0 and 479 ng C L−1 h−1 in Crooked Lake and 0–354 ng L−1 h−1 in Lake Druzhby.2. Abundance and mean cell volume both varied, producing marked changes in biomass during the year, with highest biomass occurring in the winter and early spring. Biomass showed similar seasonal trends in both lakes.3. For most of the year inorganic forms of nitrogen and phosphorus were detectable in the water columns of the lakes and were unlikely to have limited bacterial production. Dissolved organic carbon (DOC) was below 3000 μg L−1. Dissolved amino acids and carbohydrates contributed 5–25% of the DOC pool in Crooked Lake and 5–64% in Lake Druzhby. Dissolved carbohydrates were consistently low, suggesting that this may have been the preferred carbon substrate for bacterioplankton.4. Aggregate associated bacteria had higher mean cell volume, abundances and production than freely suspended bacteria in Lake Druzhby, while in Crooked Lake aggregate associated bacteria consistently had higher mean cell volumes than free bacteria, but abundance and production were on occasion higher in free bacteria compared with aggregate associated communities.5. The data indicated that production is limited by continuous low temperatures and the limited availability of suitable DOC substrate. However, the bacterioplankton functions year round, responding to factors other than temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2004.01221.x
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  • 2
    Electronic Resource
    Electronic Resource
    Virus and microbial loop dynamics over an annual cycle in three contrasting Antarctic lakes (2005)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 50 (2005), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Viral and microbial loop dynamics were investigated over an annual cycle in three contrasting saline Antarctic lakes – Highway Lake (salinity 4‰), Pendant Lake (salinity 19‰) and Ace Lake, a meromictic system (with a mixolimnion salinity of 18‰) in order to assess the importance of viruses in extreme, microbially dominated systems.2. Virus like particles (VLP) showed no clear seasonal pattern, with high concentrations occurring in both winter and summer (range 0.89 × 107 ± 0.038 to 12.017 × 107 ± 1.28 mL−1). VLP abundances reflected lake productivity based on chlorophyll a concentrations. Bacterial abundances and biomass did not correlate with VLP numbers except in Pendant Lake, the most productive of the three lakes studied.3. Pendant Lake supported the highest bacterial biomass (range Highway: 18.44 ± 1.35 to 59.43 ± 2.80 ng C mL−1; Ace: 14.42 ± 2.69 to 68.39 ± 2.95 ng C mL−1; Pendant: 31.36 ± 3.94 to 115.95 ± 4.49 ng C mL−1) so that virus to bacteria ratios (VBR) (range 30.48 ± 7.96 to 96.67 ± 8.21) were higher in Ace Lake (range 30.58 ± 3.98 to 80.037 ± 1.60) and Highway Lake (range 18.63 ± 3.12 to 126.74 ± 6.50).4. Negative correlations occurred between VLP and cryptophytes (dominant phototrophic nanoflagellates), suggesting that they were not hosts to lytic viruses. Among the other protists only the heterotrophic nanoflagellates of Highway Lake (dominated by the marine choanoflagellate Diaphanoeca grandis) showed a positive correlation with VLP.5. The VLP was negatively correlated with photosynthetically active radiation (PAR) and temperature, both of which increased with ice thinning and breakout, increasing viral decay. In winter VLP probably persisted in cold, dark water.6. High VLP concentrations and high VBR (values at the upper end of those reported for marine and lacustrine systems) indicated that viruses, most of which were probably bacteriophage, are a major element within the microbial communities in extreme, saline lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2005.01399.x
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  • 3
    Electronic Resource
    Electronic Resource
    Seasonal dynamics of the planktonic community in Lake Druzhby, Princess Elizabeth Land, Eastern Antarctica (1996)
    Oxford BSL : Blackwell Science Ltd
    Freshwater biology 35 (1996), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The temporal abundance and composition of the plankton of a continental Antarctic lake (Lake Druzhby) situated in the Vestfold Hills, Eastern Antarctica was investigated from December 1992 to December 1993. The system was dominated by microbial plankton (cyanobacteria, heterotrophic bacteria and protozoans) with few metazoans.2. Chlorophyll a concentrations ranged between 0.15 and 1.1 μg l–1 and showed highest levels from late winter to spring.3. Heterotrophic bacteria ranged between 75 and 250 × 106 l–1 with highest abundances in late winter/spring. Mean bacterial biovolumes showed considerable seasonal variation (0.05–0.31 μm3). Largest biovolumes occurred in summer and this was the time of highest community biomass.4. Heterotrophic nanoflagellates reached highest abundances in late summer (maximum 14 × 105 l–1). Their mean biovolume also exhibited considerable seasonal variation, ranging between 1.77 and 27.0 μm3, with largest size resulting in community biomass peaking in early summer. Ciliated protozoa were poorly represented and sparse. Phototrophic nanoflagellates were sparse in this lake; instead the phototrophic plankton was dominated by a small rod-shaped cyanobacterium which constituted the largest carbon pool in the system. It was common throughout the year, its biomass peaking in autumn. Its presence is discussed in relation to lake morphometry and light climate.5. Heterotrophic flagellate grazing rates ranged from 6.78 bacteria cell–1 day–1 at 2 °C to 11.8 bacteria cell–1 day–1 at 4 °C. They remove around 2% of the bacterial carbon pool per day during summer and winter.6. Nutrient levels were low and recorded in pulses. Dissolved and particulate organic carbon were also low, usually less than 3 mg l–1 and 600 μg l–1, respectively. The carbon pools were derived from autochthonous sources. This lake system is driven by bottom-up forces and lacks top-down control, which fits into the picture currently seen for continental Antarctic lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1996.00480.x
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  • 4
    Electronic Resource
    Electronic Resource
    The balance between photosynthesis and grazing in Antarctic mixotrophic cryptophytes during summer (2002)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 47 (2002), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY 1. Grazing and photosynthetic contributions to the carbon balance of planktonic, mixotrophic cryptophytes in Lakes Fryxell and Hoare in the Taylor Valley, Antarctica were measured during November and December 2000.2. The cryptophytes never became entirely photosynthetic, although carbon derived from grazing decreased in December. Individual grazing rates ranged between 5.28 and 10.08 bacteria cell−1 day−1 in Lake Fryxell and 0.36–11.76 bacteria cell−1 day−1 in Lake Hoare. Grazing rates varied temporally and with depth in the water column. In Lake Fryxell, which is a meromictic lake, highest grazing occurred just above the chemocline. Individual photosynthetic rates ranged from 0.23 to 1.35 pg C cell−1 h−1 in Lake Fryxell and 0.074 to 1.08 pg C cell−1 h−1 in Lake Hoare.3. Carbon acquisition by the cryptophyte community gained through grazing ranged between 8 and 31% during November in Lake Fryxell, dropping to between 2 and 24% in December. In Lake Hoare grazing contributed 12–21% of the community carbon budget in November and 1–28% in December. Around 4% of the carbon acquired from grazing and photosynthesis was remineralised through respiration.4. Mixotrophy is probably a major survival strategy for cryptophytes in the extreme lakes of the Dry Valleys, because perennial ice-cover severely limits light penetration to the water column, whereas these phytoflagellates are not normally mixotrophic in lower latitude lakes. The evidence suggests that mixotrophy may be a mechanism for supplementing the carbon budget, as well as a means of acquiring nutrients for growth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2002.00950.x
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  • 5
    Electronic Resource
    Electronic Resource
    Microplankton dynamics in a perennially ice-covered Antarctic lake – Lake Hoare (2004)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 49 (2004), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Temporal and spatial variation in planktonic abundance, biomass and composition were determined in Lake Hoare (McMurdo Dry Valleys, Antarctica) over two summer seasons (1996–97 and 1997–98).2. Phototrophic nanoflagellates (PNAN) dominated planktonic biomass, with a mean monthly biomass ranging between 27.3 and 40.4 μg C L−1. The deep chlorophyll maximum was mainly composed of cryptophytes (〉87% of total PNAN biomass) and varied in depth between 6 and 12 m.3. Maximum bacterial concentration was 11.8 × 105 cells mL−1. Bacterial abundance showed relatively little temporal variation, with the exception of a drop in numbers that occurred in late November of both years studied.4. Ciliates were the most successful heterotrophic protozoan group, with a mean monthly biomass (1.2–3.2 μg C L−1) being typically at least double that of heterotrophic nanoflagellate (HNAN) biomass (0.1–0.7 μg C L−1).5. Microbial processes within this lake appear to be dominated by bottom up control. The relative importance of allochthonous inputs into the lake (from the ice-cover and stream flow) and autochthonous recycling (by microzooplankton regeneration) are considered.6. Results from a horizontal transect indicate that the permanence of the main sample hole may have enhanced planktonic biomass over a relatively small spatial scale.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2004.01230.x
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  • 6
    Electronic Resource
    Electronic Resource
    Life on the edge: the plankton and chemistry of Beaver Lake, an ultra-oligotrophic epishelf lake, Antarctica (2001)
    Oxford UK : Blackwell Science Ltd
    Freshwater biology 46 (2001), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Beaver Lake, a large epishelf lake in eastern Antarctica was sampled on two occasions during the austral summer of 2000. Two sites, one 1 km offshore and another 6 km offshore were sampled at intervals to depths of 40 and 110 m, respectively.2. The lake is an end member of ultra-oligotrophic lake systems with a very low carbon pool. Dissolved organic carbon concentrations ranged between 95 and 652 μg L–1. Nutrient levels were generally low with soluble reactive phosphorus ranging from undetectable to 8.4 μg L–1, ammonium ranged between 1.8 and 5.0 μg L–1, nitrate from undetectable to 161 μg L–1 and nitrite 1.1–5.3 μg L–1.3. Chlorophyll a concentrations (0.39–4.38 μg L–1) showed an unusual distribution with the highest levels close to the lake bottom at the offshore site (110 m) where the phototrophic nanoflagellates (PNAN) displayed strong autofluorescence.4. Bacterial concentrations were low, with a maximum of 7.60 × 107 L–1, as were the concentrations of heterotrophic nanoflagellates that exploit them.5. Primary production ranged between 19.7 and 25.49 μg C L–1 day–1 and bacterial production from 0.32 to 1.15 μg C L–1 day–1.6. In common with other continental Antarctic lakes, the system was dominated by a microbial plankton. However, a dwarf variety of the calanoid copepod, Boeckella poppei, occurred below 25 m at concentrations of 3–5 L–1.7. The data suggest that primary production and bacterial production were not limited by nutrient availability, but by other factors, e.g. in the case of bacterial production by organic carbon concentrations and primary production by low temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2001.00741.x
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  • 7
    Electronic Resource
    Electronic Resource
    Viruses in the plankton of freshwater and saline Antarctic lakes (2001)
    Oxford UK : Blackwell Science Ltd
    Freshwater biology 46 (2001), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Virus-like particle (VLP) abundances in nine freshwater to saline lakes in the Vestfold Hills, Eastern Antarctica (68° S) were determined in December 1999. In the ultra-oligotrophic to oligotrophic freshwater lakes, VLP abundances ranged from 1.01 to 3.28 × 106 mL–1 in the top 6 m of the water column. In the saline lakes the range was between 6.76 and 36.5 × 106 mL–1. The lowest value was found in meromictic Ace Lake and the highest value in hypersaline Lake Williams. Virus to bacteria ratios (VBR) were lowest in the freshwater lakes and highest in the saline lakes, with a maximum of 23.4 in the former and 50.3 in the latter.2. A range of morphologies among VLP was observed, including phages with short (Podoviridae) and long tails, icosahedric viruses of up to 300 nm and star-like particles of about 80 nm diameter.3. In these microbially dominated ecosystems there was no correlation between VLP and either bacterial numbers or chlorophyll a. There was a significant correlation between VLP abundances and dissolved organic carbon concentration (r=0.845, P 〈 0.01).4. The data suggested that viruses probably attack a spectrum of bacteria and protozoan species. Virus-like particle numbers in the freshwater lakes were lower than values reported for lower latitude systems. Those in the saline lakes were comparable with abundances reported from other Antarctic lakes, and were higher than most values published for lower latitude lakes and many marine systems. Across the salinity spectrum from freshwater through brackish to hypersaline, VLP concentrations increased roughly in relation to increasing trophy.5. Given that Antarctic lakes have a plankton almost entirely made up of bacteria and protists, and that VLP abundances are high, it is likely that viruses play a pivotal role in carbon cycling in these extreme ecosystems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2001.00749.x
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  • 8
    Electronic Resource
    Electronic Resource
    Stratification and dynamics of microbial loop communities in Lake Fryxell, Antarctica (2000)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 44 (2000), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Lake Fryxell, situated in the McMurdo Dry Valleys, Antarctica, offers the opportunity to study microbial loop processes in the absence of crustacean zooplankton and other higher organisms. This is the first study of Lake Fryxell to provide detailed temporal and vertical variations of microbial loop organisms. 
2. Protozoan communities are concentrated around the chemocline (9–10 m) in Lake Fryxell. Phototrophic nanoflagellates (PNAN), heterotrophic nanoflagellates (HNAN) and ciliates formed deep maxima of 14 580, 694 and 58 cells mL−1 respectively. Although abundance and biomass at the chemocline was high, diversity of protozoa was low, Plagiocampa accounting for〉 80% of the total ciliate biomass. 
3. In the mixolimnion (4.5–8 m), protozoa were less abundant, but more diverse, with 24 ciliate morphotypes being identified within this region of the water column. Inter-annual variability of protozoan biomass and abundance was greater in the mixolimnion than at the chemocline due to more variable nutrient and prey concentrations. 
4. Physicochemical gradients in Lake Fryxell were very stable because the perennial ice cover reduced wind driven currents. As a consequence, ciliate species occurred in distinct depth strata, Monodinium being most abundant directly beneath the ice cover, Askenasia having maximum abundance at 8 m and Plagiocampa dominating ciliate biomass at the chemocline. The lack of vertical mixing reduced seasonal successions of PNAN and ciliate species. Three cryptophyte species dominated the PNAN community at all times (〉79% of total biomass).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.2000.00612.x
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  • 9
    Electronic Resource
    Electronic Resource
    Seasonal heterotrophic flagellate and bacterial plankton dynamics in a large oligotrophic lake– Loch Ness, Scotland (1998)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 39 (1998), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Bacterial production in the 0–30 m water column of Loch Ness was measured using a dual labelling procedure with [3H] thymidine and [14C] leucine between May 1993 and June 1994. In most cases the uptake of the two labels did not covary, suggesting unbalanced growth. Rates of bacterial production varied from undetectable to 46.2 μg C l–1 day–1. Highest production coincided with the period of highest primary production, but carbon derived from this source was insufficient to meet the bacterial carbon demand, which was met by allochthonous humic inputs to the system.2. Heterotrophic flagellate (HNAN) grazing rates, measured using fluorescently labelled bacteria, ranged between 10.3 and 24.5 bacteria cell–1 day–1 at temperatures between 5 and 15 °C. They removed up to 27% of the bacterial production per day.3. Heterotrophic flagellate specific growth rates ranged from 0.043 to 0.093 h–1 between 5 and 15 °C, giving generation times of 7.4–16.1 h.4. bacterial and HNAN abundances were not coupled, but the highest HNAN grazing impact related to a time of high bacterial productivity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1998.00253.x
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