Species-specific effects of gastropods on leaf litter processing in pond mesocosms

Abstract

Despite the importance of litter process- ing in aquatic ecosystems, we have an incomplete knowledge of roles that specific benthic invertebrate taxa play in leaf decomposition. We studied the effect of gastropods on leaf litter decay rates in two outdoor pond mesocosm experiments: one contrasted the individual effects of six gastropod taxa on decompo- sition of senescent red maple (Acer rubrum) leaves and another evaluated the effect of Stagnicola elodes on decomposition of senescent leaves from five common deciduous forest tree species. Decay rate of red maple leaves was significantly higher with gastropods present. Rates increased by 14-39% in the presence of the relatively large-bodied pulmonates S. elodes and Helisoma trivolvis, while the small- bodied pulmonate Physa gyrina and the prosobranchs Goniobasis livescens and Bellamya japonica had smaller, non-significant effects. S. elodes significantly increased the decay rates of black cherry (Prunus serotina), sugar maple (Acer saccharum), red maple, and red oak (Quercus rubra) leaves by 72, 41, 34, and 25%, respectively, relative to no gastropod controls. Our results suggest that some gastropod species may be important players in the processing of allochtho- nous detritus, particularly in smaller, forest-enclosed lentic systems where leaf litter inputs constitute a large portion of the energy budget.