Evaluating the combined use of feeding trials and a micrographic technique to study the natural diet of Pomacea canaliculata

Abstract

Aquatic macrophytes supply an important link in freshwater systems through their multiple functions and ecosystem services. However, invasive generalist herbivores threatened their diversity and abundance. Pomacea canaliculata, one species of invasive freshwater apple snail, shows generalist macrophyte tendencies. Information about its natural diet would allow better anticipate its impacts but diet studies determining the macrophytes species eaten in natural aquatic environments are lacking. We evaluated the feasibility of identifying and quantifying macrophyte remains in P. canaliculata digestive contents. We performed single species and multiple species trials with five pre-weighed aquatic macrophytes to record the amount ingested of each of them and then dissected the snails to analyse their digestive contents microscopically. Microscopic traits provided ways to characterize macrophytes and distinguish them in combined species trials. Identifiable macrophyte remains highly varied in both single species (4.5–58.0%) and multiple species trials (5.7–35.1%); the total percentage of identifiable remains in the latter was 51–52%. The amount of identifiable remains in the multiple species trial was in general correlated with the amount ingested of each macrophyte although in one case it was strongly overestimated due to leaf fragmentation. The microscopic identification and quantification of macrophyte remains in the digestive contents appears feasible, even with several species that differ in abundance, if feeding trials accompany gut content analyses.