Invasive species are one of the largest threats to freshwater ecosystems. New combinations of native and invasive species are the basis of the novel ecosystem concept. In the sub-tropics and tropics, the Island Apple Snail, Pomacea maculata, has been widely introduced from its native South American range. Its introduction along with other invasive species has the potential to alter ecosystem functioning through grazing of native and non-native submerged vegetation. In Lake Seminole, the most downstream impoundment in the Apalachicola-Chattahoochee-Flint watershed, P. maculata was introduced ca. 2003, and surveys have indicated rapid expansion throughout large sections of the lake in recent years. Submerged aquatic vegetation, primarily invasive Hydrilla, greatly affects seasonal water quality in Lake Seminole. P. maculata rapid expansion and increase in abundance may result in significant changes to SAV distribution and ecosystem functioning in Lake Seminole. Predicting and determine limitations on the dispersal of P. maculata in introduced ranges is crucial to understanding the extent to which this species can alter ecosystem processes. For P. maculata, the potential limiting effects of temperature and dissolved calcium were studied in a factorial bioassay based on observed gradients in Lake Seminole to determine how these factors could affect potential apple snail dispersal.
Results/Conclusions
Spatial variation occurred in calcium concentrations across the three arms of Lake Seminole and adjacent water bodies, including concentrations below generally reported tolerances for gastropods. Temperature showed temporal variation, including measurements below thresholds previously developed for P. maculata activity and survival. These results indicate that conditions in Lake Seminole and adjacent water bodies can limit P. maculata growth and survival. In the bioassay, we determined that juvenile P. maculata were significantly inhibited under the combined low temperature (18˚C) and low calcium treatments (0.7 mg/L) (p<0.0001), but under the majority of conditions tested, no inhibition was observed. Uptake of calcium for shell growth was significantly greater in higher calcium treatments and at warmer temperatures. These results suggest that invasive P. maculata will not be inhibited in large sections of Lake Seminole during most of the year under present conditions. The prospect of warming temperatures due to climate change, particularly in more temperate regions, will result in fewer days that fall below the minimum temperature threshold, and increase the suitability to successful invasion by this tropical species.