The Threat of a Nonnative, Invasive Apple Snail to Oligohaline Marshes along the Northern Gulf of Mexico

Aquatic invasive species continue to be a persistent ecological problem. Management of these species requires understanding of their impact and the conditions favorable for their occurrence. Pomacea maculata is an invasive, nonnative freshwater apple snail threatening wetlands through substantial herbivory. Recent detection of P. maculata in coastal Alabama has raised concerns regarding the susceptibility of estuarine marshes in Mobile Bay and the northern Gulf of Mexico. To evaluate this threat, mesocosms were created to examine snail response to the combined effects of salinity and plant species common to estuaries throughout the region. Over a 5-week period, snails in brackish-water mesocosms (similar to 10 parts per thousand [ppt], with Juncus roemerianus or Cladium jamaicense) became dormant and neither fed nor reproduced. Snails in freshwater mesocosms (<1 ppt, with Alternanthera philoxeroides or Sagittaria lancifolia) were active and exhibited herbivory, whereas snails in mixed salinity (similar to 5 ppt, with Typha angustifolia and Scirpus validus) exhibited some activity but minimal herbivory. In follow-up studies examining salinity and plant species individually, snails fed on palatable leaves in only freshwater and mixed salinity conditions. Further, snails in freshwater did not consume measureable amounts of S. validus, T. angustifolia, J. roemerianus, and C. jamaicense, suggesting that plant palatability of common estuarine plants may also restrict herbivory. From these results, managers are cautioned that estuarine marshes with low to mixed salinities and colonized by palatable plants may be susceptible to invasion by P. maculata.