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FILE NAME: PRINCIPAL INVESTIGATOR: OTHERS: KEYWORDS: lake, flagellate, mixotrophic, heterotrophic, cyanobacteria, grazing, bacteria,
Antarctica, limnology, microzooplankton
ABSTRACT: In conjunction with the Long Term Ecological Research (LTER) project in the
McMurdo Dry Valleys of Antarctica, lakes were monitored for microzooplankton by a team based out of
the University of Nottingham (led by Johanna Laybourn-Parry). This dataset shows grazing rates of
heterotrophic and mixotrophic flagellates found in Lakes Hoare and Fryxell at various depths and dates.
VARIABLES: location, date, depth (m), type of organism, bacteria grazing rate/h/indiv,
%bacterial biomass grazed daily
RESEARCH LOCATION: Two perennial ice-covered lakes, Lake Fryxell and Lake Hoare, in the Taylor
Valley, Southern Victoria Land, Antarctica (77°S, 162°E) were sampled. Lake Fryxell has a maximum depth of
20m and is a permanently stratified meromictic lake with a conductivity of 1.2 to 2.0 mS/cm in the upper
mixomolimnion and 4.1 to 8.4 mS/cm in the lower anoxic monomolimnion. Water temperatures during the summer
range from 0.01°C to 2.7°C, with temperature increasing with depth. The chemocline is situated at 9.5m.
In contrast, Lake Hoare is unstratified during the summer and is freshwater. It has a maximum depth of 34m.
Summer temperatures in the water column ranged between 0.01°C and 1.0°C.
METHODS: The water column was sampled at the deepest point in each lake with a 2.21 Niskin bottle,
through a hole drilled in thick ice cover (approximately 4m thick). Duplicate 60ml samples from each
depth were fixed in buffered glutaraldehyde to a final concentration of 2% and stored in the dark at
4°C prior to being analyzed for bacteria. For bacteria counts, 1-2ml samples were stained with
DAPI (4', 6-diamindino-2-phenylindole), filtered onto 0.2 µm black polycarbonate membrane filters and
then viewed under UV epifluorescence microscopy. Ten Whipple grids were counted on each filter and the
mean value determined. For cryptophyte counts, 30-50ml of sample was stained with DAPI, filtered onto
a 2.0 µm polycarbonate membrane filter and viewed under epifluorescence. Twenty Whipple grids were
counted on each filter to determine mean abundance.
Biomass values for bacteria were derived by measuring 100 cells on each preparation using a
Patterson graticule at a magnification of x1600. Mean cell volumes were converted to carbon
values by applying a conversion factor of 220fg C/µm3.
Cryptophyte biomass was calculated by measuring 50 cells on each preparation. Biovolume was
derived by applying an ellipsoid geometric shape and converted to carbon using a conversion
figure of 220fg C/µm3.
Flagellate ingestion rates were determined using fluorescently labelled bacteria (FLB). FLBs
were prepared by labelling bacteria cultured from Lake Fryxell with DTAF
[5-(4,6-dichlorotriazin-2-yl) aminofluorscein]. Ingestion rates were
measured in flagellates collected from 6m and 12m in Lake Hoare and 6m, 8m, and 9m in Lake
Fryxell. Incubations were conducted in situ at the appropriate depths using 60ml acid rinsed
Nalgene bottles. Duplicate 50ml samples were fixed with ice-cold 2% phosphate buffered
glutaraldehyde (final concentration) after 30 minutes, 1 hour, 2 hours and 3.5 hours. Samples
were stained with DAPI filtered onto a 5 µm polycarbonate filter and viewed under
epifluorescence microscopy. Four hundred cryptophyte cells were examined on each
preparation, and the number of FLB in each cell recorded. Ingestion rates were calculated using the
linear portion of the uptake curves.
TIMING: Samples were gathered on 19-Nov-1997 and 15-Dec-1997 at Lake Fryxell, and 7-Nov-1997
and 26-Jan-1998 at Lake Hoare.
CITATIONS: Roberts, Emily C. and Johanna Laybourn-Parry. 1998. Mixotrophic cryptophytes and their
predators in the Dry Valley lakes of Antarctica. Freshwater Biology. In Press.
COMMENTS:
STATUS: Restricted Access (Type IV).
VARIABLE DESCRIPTION:
VARIABLE TYPE DESCRIPTION UNITS MISSING VALUE INDICATOR MINIMUM MAXIMUM PRECISION Location Text Name of lake where measurement was made none Required entry n/a n/a n/a Date Date Date on which sample was gathered mm/dd/yy Required entry 11/01/97 01/31/98 dd Depth (m) Number Depth at which sample was drawn from lake meters Required entry 6 12 1 Type of Organism Text Category describing species none Required entry n/a n/a n/a Bacteria grazing rate/h/indiv Number Rate at which bacteria was consumed # of bacteria/hour/individual Required Entry 0 n/a 0.1 %Bacterial biomass grazed daily Number Proportion of bacterial biomass consumed in 24 hours Null 0 100 0.1 LOG: Data for this file was submitted by Johanna
Laybourn-Parry to the data manager at INSTAAR on October 21, 1998. Files were
sent via e-mail as well as a hard copy. The original version of the file is
stored on the Unix system in "/data1/data/lakes/plankton/laybourn-parry/DV".
Upon arrival at INSTAAR, the data manager reformatted the file using Microsoft
Access to present it in a relational mode. It was then exported in comma
delimited ascii and MS-DOS text format to present on the web. Links to these
files are provided above.
NOTE: Data contained in these files has been subjected to quality
control standards imposed by the investigator. The user of this data
should be aware that, while efforts have been taken to ensure that these
data are of the highest quality, there is no guarantee of perfection
for the data contained herein and the possibility of errors exists. If
you encounter questionable data, please contact the MCM LTER data manager
(; (303)492-4639) so that the data can be
corrected or qualified. Thus, these data may be modified and future
data will be appended.
Percent