Invasive non-native species often succeed in an invaded habitat because of their capabilities as generalist consumers. The trophic dynamics associated with an invasion are crucial to the invasive species’ influence on ecosystem function. As a gastropod, the invasive New Zealand mudsnail (Potamopyrgus anitpodarum) has largely been studied under the guise of only one functional group, as “scrapers” of periphyton, algae and diatoms. This study contends that as generalist consumers the snails are also acting as detritivores in stream ecosystems, and accelerating the decomposition of riparian leaf litter, which serves as an important nutrient source for native invertebrates. This study aimed to (1) determine if New Zealand mudsnails accelerate the rate of leaf litter decomposition and (2) determine how mudsnail density altered decomposition.  Leaf litter bags containing air-dried White Alder (Alnus rhombifolia) leaves were placed in an invaded Northern California creek at four different sites. The bags either allowed snails to access the litter or excluded snails. Subsets (n=6) of the bags for each treatment were removed weekly for one month, and the abundance and biomass of invertebrates was assessed for each treatment.  Decay rates of oven-dried leaf litter were assessed using a single exponent equation.

Results/Conclusions:

Results showed that there was a significant difference in percent mass loss between the two treatments. Leaf litter that was exposed to snails lost 30% of its mass over 28 days, but treatments where snails were excluded lost only  15% of leaf litter mass. The abundance of non-mudsnail invertebrates in each treatment did not differ over the course of the experiment. This suggests that native invertebrates are playing a smaller role in the breakdown and decomposition of riparian leaf litter in areas where New Zealand mudsnails have invaded.  Initial results also suggest that snail density may significantly contribute to litter decomposition. A second study underway, where snail densities are manipulated, will clarify these findings.