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  • 1
    Electronic Resource
    Electronic Resource
    Flagellate nutritional versatility as a key to survival in two contrasting Antarctic saline lakes (2005)
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 50 (2005), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Seasonal patterns of grazing and photosynthesis were investigated in two saline Antarctic lakes (Highway and Ace) in the Vestfold Hills (68°S). The phototrophic nanoflagellate (PNAN) community was dominated by Pyramimonas gelidicola and two morphological forms of a cryptophyte species that occurred throughout the year. Both species were mixotrophic on bacteria, and in Highway Lake they also exploited dissolved organic carbon as determined by the uptake of fluorescently labelled dextrans.2. Clearance rates ranged between 0.02 and 0.21 nL h−1 cell−1 in Ace Lake and 0.004–1.05 nL h−1 cell−1 in Highway Lake. On occasion cryptophyte grazing equalled that of the heterotrophic nanoflagellates (HNAN).3. Photosynthetic rates showed similar trends in both lakes, but there were differences in chlorophyll a specific rates and photosynthetic efficiency, probably related to the meromictic characteristic of Ace Lake. Primary production was measurable in winter and peaked in summer following the maxima of mixotroph grazing.4. The HNAN community of Highway Lake achieved clearance rates of 0.02–1.80 nL h−1 cell−1 and removing between 50 and 693 ng bacterial carbon L−1 day−1, with highest impact in winter when HNAN were most abundant. The HNAN also ingested fluorescently labelled dextrans showing a preference for 4 and 500 kDa molecules. The more diverse HNAN community of Ace Lake had lower clearance rates (0.04–0.37 nL h−1 cell−1) and exerted a lower grazing pressure on bacterioplankton. In Highway Lake, where the HNAN community was dominated by the choanoflagellate Diaphanoeca grandis, there was a significant correlation between mean cell volume and clearance rate.5. The major feature was that the microbial plankton functioned throughout the year by employing nutritional versatility.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2427.2005.01369.x
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  • 2
    Electronic Resource
    Electronic Resource
    Mixotrophic cryptophytes and their predators in the Dry Valley lakes of Antarctica (1999)
    Oxford, UK : Blackwell Science, Ltd
    Freshwater biology 41 (1999), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The ingestion rates of planktonic, mixotrophic cryptophytes in two perennially ice-covered Antarctic lakes in the McMurdo Dry Valleys, were investigated during the summer of 1997–1998.2. In Lake Fryxell, which is meromictic, ingestion rates increased with depth in November and were highest in a cryptophyte maximum close to the chemocline. In Lake Hoare, which is unstratified and freshwater, there was no significant difference in ingestion rates with depth. In both lakes, the highest ingestion rates occurred in early summer, decreasing in December and January. Ingestion rates varied between 0.2 bacteria cell−1 h−1 and 3.6 bacteria cell−1 h−1.3. During November, mixotrophic cryptophytes removed up to 13% of bacterial biomass day−1 and had a greater grazing impact than heterotrophic nanoflagellates (HNAN). As summer progressed, the grazing impact of cryptophytes and HNAN became similar.4. The maximum depth of cryptophytes in Lake Fryxell was predated by a population of the ciliate Plagiocampa. Plagiocampa had an ingestion rate of 0.13–0.19 cryptophytes cell−1 h−1. The grazing impact on the cryptophyte community was insignificant. However, the ciliate appeared to be indulging in temporary mixotrophy, sequestering the cryptophytes for a number of weeks before digesting them.5. It is suggested that mixotrophy is an important survival strategy in the extreme lake ecosystems of the McMurdo Dry Valleys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1999.00401.x
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  • 3
    Electronic Resource
    Electronic Resource
    E-mail: 〈email〉J.Laybourn-Parrynottingham.ac.ukAnnual〈/email〉 plankton dynamics in an Antarctic saline lake (1999)
    Oxford, UK : Blackwell Science, Ltd
    Freshwater biology 41 (1999), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. The plankton dynamics of Ace Lake, a saline, meromictic basin in the Vestfold Hills, eastern Antarctica was studied between December 1995 and February 1997.2. The lake supported two distinct plankton communities; an aerobic microbial community in the upper oxygenated mixolimnion and an anaerobic microbial community in the lower anoxic monimolimnion.3. Phytoplankton development was limited by nitrogen availability. Soluble reactive phosphorus was never limiting. Chlorophyll a concentrations in the mixolimnion ranged between 0.3 and 4.4 μg L−−1 during the study period and a deep chlorophyll maximum persisted throughout the year below the chemo/oxycline.4. Bacterioplankton abundance showed considerable seasonal variation related to light and substrate availability. Autotrophic bacterial abundance ranged between 0.02 and 8.94 × 108 L−−1 and heterotrophic bacterial abundance between 1.26 and 72.8 × 108 L−−1 throughout the water column.5. The mixolimnion phytoplankton was dominated by phytoflagellates, in particular Pyramimonas gelidicola. P. gelidicola remained active for most of the year by virtue of its mixotrophic behaviour. Photosynthetic dinoflagellates occurred during the austral summer, but the entire population encysted for the winter.6. Two communities of heterotrophic flagellates were apparent; a community living in the upper monimolimnion and a community living in the aerobic mixolimnion. Both exhibited different seasonal dynamics.7. The ciliate community was dominated by the autotroph Mesodinium rubrum. The abundance of M. rubrum peaked in summer. A proportion of the population encysted during winter. Only one other ciliate, Euplotes sp., occurred regularly.8. Two species of Metazoa occurred in the mixolimnion; a calanoid copepod (Paralabidocera antarctica) and a rotifer (Notholca sp.). However, there was no evidence of grazing pressure on the microbial community. In common with most other Antarctic lakes, Ace Lake appears to be driven by ‘bottom-up’ forces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1999.00396.x
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  • 4
    Electronic Resource
    Electronic Resource
    Leaf respiration during early plastidogenesis in light-grown barley seedlings (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 68 (1986), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Oxygen fluxes of protoplasts from different developmental regions of light-grown (16 h day/8 h dark) barley (Hordeum vulgare L. cv. Patty) seedlings were studied using oxygen electrodes as well as with a more sensitive technique of oxygen exchange measurement, Cartesian-diver microrespirometry. A pronounced increase in dark respiration of protoplasts from the region close to the intercalary meristem was observed, especially below the amyloplast region. In the dark this region also displayed the greatest activity of the alternative (cyanide-insensitive) mitochondrial electron-flow pathway, possibly due to high intracellular sugar levels and suitable cytosolic energy charge engaging the pathway. Etiolated protoplasts from similar regions of dark-grown barley seedlings close to the intercalary meristem displayed a reduced dark respiratory rate which suggests that mitochondrial participation prior to normal plastid development is a partially light-initiated process, probably acting through the agency of phytochrome and a blue light receptor. These results demonstrate that in normal light-grown seedlings, just as in algal and etiolated greening systems, mitochondrial participation is vital for the very early stages of plastid development and may be controlled at least partly through phytochrome action as well as a blue light receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1986.tb06602.x
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  • 5
    Electronic Resource
    Electronic Resource
    A hyperactive, Ca2+-dependent antifreeze protein in an Antarctic bacterium (2005)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 245 (2005), S. 0 
    Details
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In cold climates, some plants and bacteria that cannot avoid freezing use antifreeze proteins (AFPs) to lessen the destructive effects of ice recrystallization. These AFPs have weak freezing point depression activity, perhaps to avoid sudden, uncontrolled growth of ice. Here, we report on an uncharacteristically powerful bacterial AFP found in an Antarctic strain of the bacterium, Marinomonas primoryensis. It is Ca2+-dependent, shows evidence of cooperativity, and can produce over 2 °C of freezing point depression. Unlike most AFPs, it does not produce obvious crystal faceting during thermal hysteresis. This AFP might be capable of imparting freezing avoidance to M. primoryensis in ice-covered Antarctic lakes. A hyperactive bacterial AFP has not previously been reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/j.femsle.2005.02.022
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  • 6
    Electronic Resource
    Electronic Resource
    Respiratory metabolism of Cyclops bicuspidatus (sensu stricta) (Claus) (Copepoda: Cyclopoida) from Esthwaite Water, Cumbria (1980)
    Springer
    Oecologia 46 (1980), S. 386-390 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The respiration rate of all stages of Cyclops bicuspidatus (s. str.) (Claus), a benthic copepod, from Esthwaite Water in the English Lake District, was determined at a range of field temperatures, 4° C–12° C, using cartesian diver microrespirometry. The population of C. bicuspidatus in Esthwaite Water was found to be adapted to low temperatures, with an optimum rate of metabolism at 8° C. Weight varied with temperature, in general the largest weights occurred at the lower temperatures. Adult males had higher rates of respiration than adult females, which were on average twice the size of males. Gravid and non-gravid females had similar levels of metabolism. Regression coefficients (b), derived from regressions of log oxygen consumption against log dry weight were low, ranging between 0.25–0.51 according to temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00346268
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  • 7
    Electronic Resource
    Electronic Resource
    Microbial communities in saline lakes of the Vestfold Hills (eastern Antarctica) (1997)
    Springer
    Polar biology 18 (1997), S. 135-144 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A detailed survey was undertaken of the microbial communities of 16 saline lakes in the Vestfold Hills (Princess Elizabeth Land, eastern Antarctica), which ranged in salinity from slightly brackish (4–5‰) to hypersaline (maximum: 174‰). Temperatures at comparable sampling depths in the lakes ranged from −12.2°C to +10.5°C. Ranges in the abundances of bacteria, heterotrophic nanoflagellates (HNAN) and phototrophic nanoflagellates (PNAN) were 1.40 × 107 l−1–1.58 × 1010 l−1, 4.83 × 104 l−1–1.70 × 107 l−1 and 0–1.02 × 107 l−1, respectively. There was considerable variation across the salinity spectrum, though in the case of bacteria and PNAN significantly higher concentrations of cells were seen in two of the most saline lakes. The autotrophic ciliate Mesodinium rubrum occurred in all but five of the lakes and was found at salinity levels up to 108‰. Heterotrophic ciliates were generally scarce. Dinoflagellates, particularly Gonyaulax c.f. tamarensis, Gyrodinium lachryma and Gymnodinium sp., occurred in the majority of the lakes. On the basis of chlorophyll a concentrations, nutrient levels and microplankton concentrations the lakes spanned the spectrum from ultra-oligotrophic to oligo/mesotrophic. The most saline lakes had much reduced species diversity compared with the less saline environments. Isolation from the marine environment has led to nutrient depletion, simplification and a truncated trophic structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003000050168
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  • 8
    Electronic Resource
    Electronic Resource
    The microbial plankton of freshwater lakes in the Vestfold Hills, Antarctica (1992)
    Springer
    Polar biology 12 (1992), S. 405-410 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The plankton of twelve freshwater and slightly saline lakes in the Vestfold Hills, Antarctica was sampled in February 1991. All of the lakes are oligotrophic. The chlorophyll a concentrations in the lakes ranged from 0.10–2.69 μg · 1−1. The majority of the phytoplankton were flagellates or picoplanktonic cyanobacteria with the species composition varying between the lakes. Cyanobacteria were found in five of the lakes. Five to 6 species of ciliated protozoa occurred, among them oligotrichs, including the mixotrophic species Strombidium viride. The concentrations of protists and bacteria were an order to several orders of magnitude lower than reported from lower latitude oligotrophic lakes. Low species diversity and low numbers in the plankton characterise these eastern Antarctica lakes which reflects their low nutrient status and isolation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00243111
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  • 9
    Electronic Resource
    Electronic Resource
    Seasonal cycle of the microbial plankton in Crooked Lake, Antarctica (1992)
    Springer
    Polar biology 12 (1992), S. 411-416 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Changes in the abundance of the components of the microbial plankton between July 1990 and March 1991 in Crooked Lake, one of the largest and deepest freshwater lakes in Antarctica, are described. Chlorophyll a concentration is low (0.2–0.4μg·1−1) and there is no discernable spring increase. The phytoplankton is largely dominated by flagellates. Bacterioplankton exhibits a seasonal pattern of abundance ranging from 1.0 × 108·1−1 in July to 3.25 × 108·1−1 in September. Changes in bacterial abundance probably relate to temperature and grazing by heterotrophic and mixotrophic flagellates. Total flagellated protozoan concentrations ranged between 25–136 × 102·l−1. Autotrophic and heterotrophic flagellate abundances were coupled and peaks in their abundance oscillated with peaks in bacterioplankton concentration. Four species of ciliated protozoa, dominated by oligotrichs, particularly the plastidic Strombidium, inhabit the lake. The plankton is characterised by the presence of floes which act as loci for bacteria, flagellates and amoebae and feeding sites for the ciliates and the two sparce metazoan components of the plankton. Crooked Lake is extremely oligotrophic but nonetheless supports a plankton community with a low species diversity and simple trophodynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00243112
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  • 10
    Electronic Resource
    Electronic Resource
    The plankton community of a young, eutrophic, Antarctic saline lake (1999)
    Springer
    Polar biology 22 (1999), S. 248-253 
    Details
    ISSN: 1432-2056
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A shallow, saline lake (Rookery Lake) close to the sea and surrounded by a penguin rookery was investigated during the austral spring and summer of 1996/1997. The proximity to the sea means that the lake is likely to have been formed recently during isostatic uplift. Inputs of carbon and nutrients from the penguin rookery have rendered Rookery Lake eutrophic compared with other brackish and saline lakes in the Vestfold Hills. Chlorophyll a concentration, bacterioplankton, heterotrophic nanoflagellate and phototrophic nanoflagellate abundances were all significantly higher than in other non-enriched lakes. The high productivity created seasonal anoxia during winter and spring below ice cover. The ciliate community resembled the marine community, and was dissimilar to that seen in older saline lakes within the Vestfold Hills. Thus Rookery Lake provides valuable evidence of the impact of natural eutrophication on an Antarctic lake, as well as of the evolution of the typical microbial community which dominates the older lakes of the Vestfold Hills.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003000050417
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