The effect of snails on leaf litter processing in aquatic systems

Despite the importance of litter processing in aquatic ecosystems, we have an incomplete knowledge of how aquatic community structure affects leaf decomposition rates. We studied the effect of gastropods on leaf litter decay rates in a pair of pond mesocosm experiments. In the first experiment we tested the effect of six snail species on decomposition of senescent red maple leaves. Averaged across species, snails significantly increased the decay rate of red maple leaves relative to no snail controls. Stagnicola emarginata, Helisoma trivolvis, and Stagnicola elodes had the greatest effect on leaf decomposition, increasing the rate of decay by 39%, 27%, and 14%, respectively. Physa gyrina, Goniobasis livescens, and Bellamya japonica had smaller effects on leaf mass loss. In a second experiment we measured the effect of Stagnicola elodes on the decay rates of senescent leaves of five common deciduous forest tree species. Stagnicola elodes significantly increased the decay rate of black cherry, sugar maple, and red maple leaves by 72%, 41%, and 34%, respectively, relative to no snail controls. Although snails are not commonly considered to function as shredders, our data suggest that some species may exert a significant influence on the rate of leaf decay in aquatic systems.