PARENT SESSION
Poster Session 3: Aquatic Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 210 D, Level 2, Palais des congrès de Montréal

The distribution and abundance of Hyalella azteca across an emergent vegetation to open water gradient in a prairie pothole wetland.

Christensen, Jay¹, ¹ Iowa State University, Ames, IA

ABSTRACT- Emergent vegetation predominates in depressional wetlands within the Prairie Pothole Region of the Midwest. Cattails (Typha spp) form dense stands which reduce dissolved oxygen (DO) concentrations. The transition from open water to emergent vegetation produces opposite gradients of emergent vegetation and DO. Both factors influence distribution and abundance of wetland invertebrates, which are an important trophic link in prairie potholes. It is hypothesized that invertebrates will be more abundant in the transition zone where emergent vegetation and DO concentrations are moderately abundant. Quantitative measurements of a representative organism, Hyalella azteca, were taken from May to October of 2004 across the vegetation gradient in a natural prairie pothole. Samples were taken at 10 meters into the cattails (emergent zone), at the emergent-open water interface (transition zone) and 8 meters out in the open water (open water zone). Water temperature and DO measurements were taken. Quantitative samples of plant species were taken and dry weights were determined. DO measurements differed significantly for zones and months. However, DO was not correlated to H. azteca densities. H. azteca densities differed significantly between the open water zone and the other two zones. Densities shifted between the transition zone in June to the emergent zone in August and equilibrated in the fall. This shift was not correlated to Typha spp dry weight, but was correlated to amounts of non-rooted floating plants (r²=.45), consisting mainly of Lemna trisulca and Spirodela polyrhiza. The lack of response of H. azteca to DO levels may be explained by a possible compression of the vertical profile of H. azteca under hypoxic conditions in the emergent zone. The high correlation of H. azteca abundance to Lemnaceae abundance could be due to preferred habitat for feeding and/or a refuge from predation by other invertebrates and fathead minnows. H. azteca abundance and distribution seem to be influenced more by non-rooted floating plant abundance than by gradients of cattail densities or dissolved oxygen concentrations in this prairie pothole wetland.

Key words: Hyalella azteca, Pairie Pothole wetlands, Lemnaceae, dissolved oxygen