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.

The influence of an invasive macrophyte (Myriophyllum spicatum L.) on littoral and pelagic zooplankton community structure.

Rogers, Kristy ¹, Soranno, Patricia ¹, ¹

ABSTRACT- In many lakes, macrophyte beds provide the main physical structure for the littoral zone. By increasing spatial heterogeneity, macrophytes offer colonizable habitat as well as refuge from predation for aquatic organisms, especially zooplankton. Often, exotic plants that invade and dominate a lake significantly alter this physical structure. Thus, we hypothesize that changes in exotic macrophytes will alter the zooplankton community. In this study, we examined the effect of the exotic macrophyte Eurasian watermilfoil (Myriohphyllum spicatum L., EWM) on both littoral and pelagic zooplankton community structure through a whole-lake manipulation study. We measured zooplankton for three years (before, during and after treatment) in two lakes: one lake was manipulated by reducing the % EWM cover in the lake by 33%, while the other lake served as the control lake with high EWM cover. We found that although reducing % EWM coverage in a lake did not appear to affect the relative dominance of zooplankton among taxonomic groups (cladocerans, copepods and rotifers), it did alter the species composition within these taxonomic groups in both the pelagic and littoral zones. In particular, following EWM reductions in the treatment lake, we found that the smaller bodied cladocerans had been replaced by Daphnia in both the littoral and pelagic zones. These results suggest that moderate changes in the macrophyte community have the potential to exert relatively large effects in both littoral and pelagic zone foodwebs.

KEY WORDS: zooplankton, macrophytes, lakes, Eurasian watermilfoil