Snail-macrophyte interactions in a shallow, mesoeutrophic lake in southern New York State
The objective of this research was to investigate trophic interactions between snails and macrophytes in freshwater benthic systems. Surveys of the snail and macrophyte communities of Calder Lake revealed Armiger crista, a recent introduction to Calder Lake, to be the most abundant snail. Macrophyte species composition in the lake was highly variable between years, with Vallisneria americana dominance in 1993 being replaced in the following year by Elodea canadensis. Snails in Calder Lake were found to associate preferentially with V. americana compared to Najas flexilis, Potamogeton amplifolius, and allochthonous leaf litter. Snail grazing on epiphytes may indirectly increase macrophyte biomass. Therefore, I conducted a sunfish (Centrarchidae) enclosure/exclosure experiment to determine whether sunfish predation on snails would have cascading effects on epiphytes and macrophytes in Calder Lake. Sunfish enclosure decreased A. crista densities. Densities of other snail species were not affected by sunfish enclosure, possibly due to the availability of a wide variety of sunfish prey. Sunfish predation on snails did not have cascading effects to epiphytes and macrophytes. Laboratory studies were also performed to investigate the potentially mutualistic relationship between snails and macrophytes. I conducted a study in which V. americana plants at two epiphyte densities (low and high) were exposed to varying densities of Physa gyrina snails. Results indicate that snails may benefit macrophytes via epiphyte removal, however high snail densities may lead to depleted epiphyte resources and subsequent macrophyte consumption. I conducted similar studies of increasing snail densities on apical portions of four macrophyte species under two epiphyte densities (low and high). Results were mixed, with epiphyte presence appearing to stimulate snail grazing of N. flexilis and P. amplifolius. I also conducted a study examining the effect of fish, submersed aquatic vegetation (SAV) and zebra mussels on epiphyte biomass and snail growth and survivorship. SAV reduced epiphyte biomass, while fish had the opposite effect. SAV increased adult snail survival but reduced adult snail growth rates. Zebra mussels increased adult snail growth rates.
Gorham, Bernadette Kathleen, "Snail-macrophyte interactions in a shallow, mesoeutrophic lake in southern New York State" (1997). ETD Collection for Fordham University. AAI9730091.