populations

A population is a group of organisms of the same species. Like canaries in the coalmine, changes in populations of organisms can be important indicators of environmental changes.

Stream Algal Abundances

Abstract: 

As part of the Long Term Ecological Research (LTER) project in the McMurdo Dry Valleys of Antarctica, a systematic sampling program has been undertaken to monitor the abundance and species distribution of algal mats in glacial meltwater streams of the region. This table contains data showing the percent of total biomass (abundance) represented by algal type (brown, red, orange or green), phylum, species and morphotype for multiple streams, dates, and replications.

Dataset ID: 

12

Core Areas: 

Short name: 

strmalgi

Methods: 

Within each transect, algal mats were visually identified as either orange, red, black, or green. Not all types of algal mats were found within every transect. A maximum of five algal samples of each color were collected from each transect using a #13 cork borer (diameter = 17 mm, area = 227 mm2). Algal samples were preserved in 10% formalin for laboratory identifications. In all, 141 algal samples were collected from 12 streams. Preserved algal samples were examined in the laboratory to determine species composition and relative abundance using a Nikon Diaphot phase contrast microscope. Samples were well mixed to attain an even (random) sampling of mat (some small "clumps" of algae were still present, but these did not affect the objectives of the study), and then subsamples of 2 ml were withdrawn. Each subsample was placed in a 2-ml settling chamber with a 26 mm diameter and examined at x400 magnification. To get a representative count of relative species abundance, seven random fields (a total of 0.44 mm2) needed to be examined per subsample. Within each field, algae were identified to genus and species where possible (excluding diatoms, which were counted but not identified.) Percent cover was determined in each field by measuring the length and width of all specimens using an ocular micrometer. Cell "depth" was also measured in order to estimate biovolume. All seven fields were then tallied, and the percentage of the total algal biomass was determined for each taxa. Taxonomic identifications were primarily based on the classical Antarctic literature.

Data sources: 

strmalgi

Maintenance: 

Data from this table was initially included in the raw data files specified under the variable for 'file name'. These are Microsoft Excel version 6.0 files. Once submitted to INSTAAR, the data manager combined all of the stream biology files that included variables for "abundance", and removed any variables that had no direct influence on the total biomass (abundance) of a given algal type, phylum, species, and morphotype. The resulting table is represented in the "strmalgi.dat" (ascii comma delimited format) and "strmalgi.txt" (MS-DOS text - table layout) files used on the web page. In November, 1999, the data manager added a field for stream transect ID code. This assisted in preparing the data for use in Oracle and ArcInfo. In July, 2000, the dataset code field was added in order to simplify generating links between different data and metadata fields.

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