Mute Swan (Cygnus Olor) Impact on Submerged Aquatic Vegetation and Macroinvertebrates in a Rhode Island Coastal Pond

We followed the annual use of a shallow coastal pond by molting Mute Swans to examine their potential impacts on waterfowl habitat. Effects of Mute Swan herbivory on submerged aquatic vegetation (SAV) and macroinvertebrates were measured by comparing control vs. exclosure plots in varying water depths from 1990 to 1994. Mute Swans fed in all water depths, but appeared to prefer feeding in shallow sites (< 0.5 m) where they were capable of reducing SAV biomass by up to 95%. The impact of Mute Swans on macroinvertebrates could not be demonstrated. Only three species of macroinvertebrates (Grammarus spp., Hydrobia spp., Limnephilus spp.) showed reduced densities on some grazed plots.