The 1990s introduction of semi-aquatic apple snails (Pomacea spp.) to the Southeast United States poses a potentially significant impact to current natural and managed wetlands. Native to South America, these snails have caused substantial economic problems for rice and taro wetland crop production in Asia, however there are concerns they may affect sensitive natural water systems present in Florida. In 2018, we implemented a four month (June-September) mesocosm experiment in central Florida wetlands invaded by Pomacea maculata. Biweekly measurements were taken for water quality, vegetation cover, and pre/post experiment measurements were taken for plant biomass, soils and snail weight/sizes. We ask how invasive P. maculata affect ecosystem functioning (i.e. plant biomass, nutrient dynamics, and water quality) and whether their effects are mediated by management intensities of wetlands (i.e., high vs. low intensity). We hypothesize that through excessive consumption and preferential feeding, apple snails could decrease plant biomass, species richness, and vegetation cover. Consequently, they may increase nutrient releases into the water column, alter nutrient cycling in soils, and facilitate the growth/dominance of algae. We anticipate that snails may exhibit stronger effects on high intensity wetlands since they are less diverse, more disturbed, and thus more susceptible to invasion effects.
Results/Conclusions
Snails increased in size in both wetland types, but their weight increased ~ 1.6 times more in high- than low-intensity mesocosms, likely due to greater productivity and thus more biomass available for consumption in the high-intensity wetlands. Similar results were found for their other dimensions height, length, and width (1.75 times more in high intensity, 1.8 times, 1.9 times respectively). We also found significant interactions between snail treatment and wetland type effects on aboveground plant biomass (p=0.0016), in which greater negative effects (-262 g/m2 per mesocosm vs. -137.44 g/m2 per mesocosm) were found in high- than low-intensity mesocosms. Snails appear to exhibit feeding preferences resulting in greater impacts on forbs (Bacopa caroliana, Justicia angusta) and emergent macrophytes (Pontedaria cordata) than on grasses (Panicum Hemitomon, Amphicarpum muehlenbergianum). Initial analysis on soil nutrient pools showed no effect of snails. Additionally, water quality parameters do not appear to change drastically over time, however preliminary results indicate snails may have differential effects on algae populations in high- and low-intensity wetlands. Our further analysis will examine how effects on aboveground plant communities cascade to soil and water nutrient cycling in this system.