The invasive apple snail (Pomacea maculata), native to South America, has caused significant impacts on agricultural wetlands and rapidly spread to surrounding natural areas through river systems in the Southeastern United States. In addition to economic losses, this invasion may change ecosystem functioning and compromise vital wetland services by altering vegetation and water chemistry. Invasive apple snails may cause important consequences for nutrient cycling by affecting litter decomposition (1) directly through changing environmental conditions and promoting micro-decomposers by suitable substrates in its excretions. In this study, we designed a wetland mesocosm experiment with a 2x2 factorial design (N = 8) to manipulate presence/absence of apple snails (i.e., introducing 8 snails to invasion treatment), and level of wetland management intensity (i.e., high vs. low intensity in terms of nutrient inputs.), representing major wetland types in south-central Florida. The litter bag technique (4 grams, collected to represent dominant vegetation in each wetland type), was used to quantify remaining litter biomass from 14, 28, 56, 98 days after deployment in each mesocosm, respectively. Our design also allows us to examine how effects on decomposition vary with land management intensity.
Results/Conclusions
Dominant vegetation in the two wetland types had different litter qualities: plants in low intensity wetlands contained higher C, Ca, C/P ratio, and lignin concentration, and plants in high intensity wetlands contained higher P, K, and Mg concentration. Remaining litter biomass for each mesocosm were fitted to non-linear asymptote exponential decay models to determine decay rate and asymptote. Although invasive apple snails and wetland type did not seem to have significant effects on litter decay rate, they showed an interactive effect on the fraction of litter remaining (asymptote). Litter in low intensity wetland mesocosms had a higher fraction of recalcitrant material and was resistant to the indirect effects of snails, which is likely due to lower P concentration and higher lignin content. However, litter in high intensity wetland mesocosms had a lower fraction of recalcitrant material and the presence of snails significantly reduced this fraction. Over the course of the experiment, remaining litter nutrient concentrations in the snail treatment were higher in N, P, K, Mg, Ca, and such effects increased over time and was greater in high intensity wetland mesocosms. Collectively, our results show significant indirect effects of invasive apple snails on recalcitrant content and nutrient composition of litter materials especially in wetlands with enriched nutrients.