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

Spatial ecology of predator and prey in a Minnesota Lake.

Hembre, Leif^*,1, Spitael, Maria², Megard, Robert², McAlpine, Rachel¹, Hondzo, Miki², ¹ Hamline University, St. Paul, MN, USA² University of Minnesota, Minneapolis, MN, USA

ABSTRACT- The physical and chemical conditions (e.g., light, temperature, water movements, oxygen concentrations) of a water column set the stage for interplay among biological actors. In this study we examine how seasonal changes in the structure of the water column affect interactions among a zooplankter (Daphnia) and its predators (rainbow trout and Chaoborus). High frequency sonar was used to examine the spatial distribution and abundance of both predators and their prey. These data show that the patterns of spatial distribution of the prey and predator populations changed substantially from spring to autumn as the water column became more strongly stratified. Throughout the year, zooplankton patchiness was consistently lowest at depths where the water column was most stable. The densest aggregations of Daphnia occurred in the deep metalimnion where energy dissipation levels were low and oxygen concentrations were between 1-5 mg/L. These depths appear to be a refuge for Daphnia from their predators. Sonar data show that trout are most abundant just above these depths where oxygen concentrations are relatively high (> 5 mg/L), and that Chaoborus occupy the deeper anoxic water just below the Daphnia maxima. Our findings imply that knowledge of the spatial complexity of an ecosystem is critical to understanding potential interactions among populations.

Key words: Daphnia, sonar, patchiness