Microzooplankton : Flagellate Grazing in Lakes Hoare and Fryxell


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.

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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 degrees C prior to being analyzed for bacteria. Fo bacteria counts, 1-2ml samples were stained with DAPI (4', 6-diamindino-2-phenylindole),filtered onto 0.2 microm 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 microm 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/microm3. 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/microm3. 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 microm 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.


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.


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