Interactions Between Epiphytes, Macrophytes and Freshwater Snails: A Review

Epiphyton-feeding snails are often a conspicuous feature of the invertebrate fauna associated with submerged freshwater macrophytes. In this paper I review the different interactions taking place between snails, epiphyton and macrophytes. Studies on grazing by freshwater snails show that snails have a great impact on the biomass, productivity and species composition of epiphytic communities. Direct effects of grazing on living macrophytes are probably of minor importance, but snails have a significant indirect effect on macrophytes by reducing the detrimental impact of epiphyton (e.g. shading and competition for nutrients). Predators of snails can have a mediating effect on snail-epiphyton-macrophyte interactions, both through a direct predatorprey relationship (reducing the density of snails) and by inducing a habitat displacement of the snails. In a study on the effects of predation by the pumpkinseed sunfish (a specialized snail predator) it was found that predation indirectly affects the biomass and species composition of epiphytic algae by regulating the density of snails.