PARENT SESSION
Poster Session 6: Arctic and Alpine Ecology
Tuesday, August 9, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Characterizing Streams of the McMurdo Dry Valleys of Antarctica though Diatom Community Composition.

Horn, Shannon ^{*,1, 2}, Esposito, Rhea ^{1, 2}, Cox, Michael^{1, 2}, McKnight, Diane^{1, 2}, ¹ Institute for Arctic and Alpine Research at the University of Colorado, Boulder, CO, USA² McMurdo Dry Valleys Long Term Ecological Research, Boulder, CO, USA

ABSTRACT- Glacial melt-water streams in the McMurdo Dry Valleys of Antarctica are distinct from one another in diatom community composition, yet these differences are too small to affect ecosystem-wide diatom community assemblages. Stream flow occurs for 6-10 weeks during the austral summer when the glaciers melt. However, this environment is very unpredictable; warmer years yield heavier flow and in colder years many of the streams never flow. Our data includes both extremes. To understand the effects of this variable climate system, we studied algal mat cores taken between 1994 and 2003 from 5 streams (data available at huey.colorado.edu/diatoms). This study focuses on diatoms because of their high species richness, compared to cyanobacteria and other organisms in the environment. Several replicate samples were taken from each stream during each year, to control for patchiness. Applying Principle Components Analysis (PCA) shows little temporal variability within a particular stream through the ten-year period despite large variability in annual stream flow; in effect the streams appear to maintain community composition. Applying Discriminant Function Analysis where time is not considered reveals distinct assemblages between the streams; conversely when location is not considered distinct yearly assemblages are revealed. These tests, with 85-94% explainable variation, allow us to infer that small differences in community composition exist between years within a given stream. However, when analyzed on an ecosystem level, these trends are not strong enough to classify each year as a separate community. The same is true of inter-stream variability. Although the environment of this cold desert is quite hostile and experiences a wide range of flow patterns throughout the summer, diatom community composition has remained stable on an ecosystem level despite small scale temporal and spatial variability.

Key words: diatoms, Antarctica, variability, communities