Juvenile snails, adult appetites: Contrasting resource consumption between two species of applesnails (Pomacea)

Research on aquatic snails usually examines consumption of periphyton, but emergence of large, invasive aquatic snails that prefer macrophytes has necessitated a new understanding about snail herbivory. Ample research exists detailing invasive potential of certain species of applesnails, such as Pomacea canaliculata, to successfully invade aquatic ecosystems. However, very few studies examine differences in resource utilization between different size-classes within species, or between closely-related species. To quantify these potential differences, we compared per mass resource consumption at two life history stages by P. canaliculata and a lesser-known species recently identified in Texas (USA), Pomacea insularum. We presented adult and juvenile snails with whole and reconstituted forms of Lactuca sativa longifolia (romaine lettuce), Myriophyllum spp. (watermilfoil), and Eichhornia crassipes (water hyacinth). In addition, we added chemical extracts to reconstituted watermilfoil and water hyacinth to test if extracts deterred consumption. Addition of periphyton to reconstituted watermilfoil allowed us to examine supplementary structure and chemistry. Juveniles seemed to prefer reconstituted resources. All snails, regardless of life-history stage, avoided water hyacinth in either form. Chemical extracts from both water hyacinth and watermilfoil deterred consumption by all snails. When presented with reconstituted watermilfoil containing additional periphyton, juvenile P. insularum consumed more resource with additional periphyton. In contrast, periphyton presence did not produce a noticeable effect on P. canaliculata consumption. Overall, juveniles of both species consumed considerably more by mass than their respective adult counterparts. Through increased numbers and difficult detection, juvenile applesnails could feasibly consume a greater proportion of plant biomass than adult applesnails and this may partially underlie the success of global applesnail invasions.