Native snails choose an invasive macrophyte over a native macrophyte as a food resource

Invasive species cause ecological and economic impacts on invaded ecosystems, although the presence of native species hampers the propagation of invasive species due to biotic resistance. We tested the effects of grazing by the native channeled applesnail (Pomacea canaliculata (Lamarck, 1828)) over the invasive macrophyte Hydrilla verticillata (L. f.) Royle (water thyme) and the native macrophyte Egeria najas Planch to evaluate the potential of herbivory as a mechanism to resist invasion. Both macrophyte species were offered, individually and combined, as food resources to the snail to evaluate its feeding preference. The macrophyte energy content and stiffness were also measured. The results indicate a higher H. verticillata biomass consumption by P. canaliculata when this macrophyte was available both individually and combined with E. najas, suggesting that H. verticillata is more palatable to the snail, despite this macrophyte being stiffer than the native one. Therefore, P. canaliculata may offer resistance to H. verticillata invasion. The feeding preference and high rates of herbivory by this snail on H. verticillata likely are associated with the higher energy content of the invasive, compared with the native, macrophyte. Experiments combining different food availabilities and snail densities are necessary to evaluate the biological control capacity of P. canaliculata under different scenarios.