PARENT SESSION
Oral Session #77: Aquatic Ecology: Food webs, invertebrates. Presiding: R.A. Washington-Allen.
Friday, August 10, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.

Effects of the exotic macrophyte, Myriophyllum spicatum, on littoral and pelagic zone foodwebs: results from whole-lake macrophyte manipulations.

SORANNO, PATRICIA¹, BREMIGAN, MARY¹, CHERUVELIL, KENDRA¹, HANSON, STEVEN¹, MOORE, VERN¹, ROGERS, KRISTY¹, VALLEY, RAHMAN¹, MADSEN, JOHN², ^{1 2}

ABSTRACT- Submerged macrophytes are a major structuring feature of many lake littoral zones, and have the potential to strongly influence not only littoral zone foodwebs, but also pelagic foodwebs. In this study, we test the hypothesis that changes in submerged macrophyte communities following invasion of an exotic macrophyte species (Myriophyllum spicatum, watermilfoil) will lead to large changes in both pelagic and littoral foodwebs. We test this hypothesis through two whole-lake studies. In the first study, we measured both pelagic and littoral zone foodwebs in a treatment and a reference lake before, during and after reduction in milfoil abundance. In the second study, we evaluated pelagic and littoral foodwebs along a gradient of watermilfoil abundance in six lakes with contrasting densities of milfoil. In the pelagic zone, we measured zooplankton, nutrients, and algae. In the littoral zone, we measured macrophytes, zooplankton, fish and epiphytic macroinvertebrates. We found relatively large effects of changing macrophyte communities on both littoral and pelagic foodwebs, although the strength of interactions varied with trophic level. Effects of macrophytes were strongest on littoral and pelagic zooplankton, adult fish, and water clarity. For example, for pelagic zooplankton, we found an increase in the large-bodied Daphnia after macrophyte manipulation. These results show that changes in macrophytes due to invasion of an exotic macrophyte species can lead to changes in both pelagic and littoral foodwebs.

KEY WORDS: macrophytes, myriophyllum spicatum, lake foodwebs