Assessing interactions among native snails and the invasive New Zealand mud snail, Potamopyrgus antipodarum, using grazing experiments and stable isotope analysis

Abstract

The New Zealand mud snail, Potamopyrgus antipodarum, is an invasive snail that can impact native snail populations. However, conflicting results from competition experiments between native snails and P. antipodarum have resulted in ambiguity about the type of impacts of P. antipodarum on native snails. We conducted grazing trials with the native North American snail, Fluminicola sp., and P. antipodarum to increase the understanding of possible impacts of P. antipodarum on this native snail. We also conducted stable isotope analysis for snails at two locations: one with P. antipodarum present and the other without this invasive snail. Based on treatment fecal mass, no significant difference was seen for grazing trials; however, single species treatments showed 4.8 times higher gram-specific fecal mass in P. antipodarum than Fluminicola sp., suggesting that P. antipodarum is a more efficient grazer. Carbon stable isotopes suggest that these snails share food resources at the invaded location. Strong overlap in food sources for P. antipodarum and Fluminicola sp. may indicate competition for food and a shift in the food resources used by Fluminicola sp. in invaded areas.