A lentic dweller in lotic habitats: the behavior of the invasive South American apple snail Pomacea canaliculata in flowing water

The aim of this study was to test the hypothesis that positive rheotaxis and anti-detachment behaviors contribute to the persistence of Pomacea canaliculata in lotic environments. This invasive apple snail is commonly considered a lentic dweller. In a first series of trials in a laboratory flume, current velocity was gradually increased until snails’ detachment. Detachment velocity was highly variable, with some snails able to withstand strong currents during short periods. Sexually undifferentiated snails were the most resistant to detachment; most of the snails that resisted high velocities were facing flow before detachment. In a second series of trials, snails’ net displacement was estimated at three fixed velocities (0, 0.15, and 0.30 m s⁻¹). Current velocity did not influence mean net displacement, which was not different from zero. Marked snails were released in a stream and recaptured 24 h later estimating their net displacement. Most recovered snails dispersed a short distance from the release point and crawled through sites with very low current velocities. A small proportion of snails drifted downstream, indicating the existence of different dispersal mechanisms. Snails were able to resist current velocities that are among the highest recorded in streams in the Pampas region. P. canaliculata did not show a positive rheotactic response; in flowing water, snails crawl more often upstream, but at a slower pace than downstream. At the population level, a slow upstream spread seems possible in plain’s streams, probably being enough to compensate drift, but not to colonize headwaters. Irrigation systems are feasible pathways for the spread of this species in invaded regions.