Macrophyte-Waterfowl Interactions: Tracking a Variable Resource and the Impact of Herbivory on Plant Growth

Abstract

Submerged macrophytes are important for the maintenance of clear water in shallow eutrophic lakes (Jeppesen et al., 1990; Scheffer, 1990; Hargeby et al., 1994), and establishment of permanent macrophy te coverage is an important aspect of the lake restoration process after a reduction of nutrient loading. However, as macrophytes are subject to grazing by herbivores such as waterfowl (e.g., Lodge, 1991), it may be speculated whether waterfowl grazing can delay recolonization and thereby lake recovery. The impact of waterfowl grazing on macrophytes is poorly documented (Winfield, 1991), and few studies have considered it important, examples being Jupp and Spence (1977), who ascribed growth limitation of Potamogeton filiformis and Potamogeton pectinatus to wave action and waterfowl grazing, and van Donk et al. (1994), who observed that intensive coot herbivory in Lake Zwemlust (up to 120 individuals/ha) affected Elodea biomass and species composition.