Consumption, survival and growth in the invasive freshwater snail Pomacea canaliculata: does food freshness matter?

Understanding factors that determine the fitness of invasive species may help us predict their spread and impact. Previous studies of the survival, growth and reproduction of Pomacea canaliculata, a freshwater apple snail native to South America now widely spread in Asia, North America and Hawaii, have emphasized the use of fresh leaves as food. We compared the consumption and growth of P. canaliculata reared on fresh and decaying leaves of three species of macrophytes with contrasting content of phenolics (general plant defence chemicals) and nutrients. We conducted 1-day consumption assays using adult snails and a 1-month survival and growth experiment using snails of various sizes. Our results showed that the consumption, survival and growth of P. canaliculata were determined by plant nutrients and phenolics, rather than plant freshness. For Murdannia nudiflora, a species with low phenolic content, fresh leaves with high nitrogen content were more palatable and valuable for growth than decaying leaves with low nitrogen content. Survival was high and not different between the fresh and decaying leaf treatments. For Myriophyllum aquaticum, decaying leaves with moderate nitrogen and low phenolic contents were more palatable and valuable for snail survival and growth than fresh leaves with high nitrogen and high phenolic contents. For Polygonum barbatum, a species with low nitrogen and medium phenolic contents, both fresh and decaying leaves were unpalatable, resulted in low snail survivorship, and did not support snail growth. The results thus indicate that P. canaliculata can utilize both fresh and decaying leaves of adequate levels of nutrients and low levels of phenolics. This dietary flexibility may have contributed to its successful colonization of many types of freshwater wetlands in regions where high-quality fresh leaves are not available throughout the year.