Inventory of New Guinea Flatworm (Platydemus manokwari) and native snails in Everglades National Park and Big Cypress National Preserve to inform invasive species management

Collins, Timothy; Lopez, Lawrence

The New Guinea Flatworm (Platydemus manokwari), sometimes abbreviated as NGF, is a non-native terrestrial predator of snails and other invertebrates that has been introduced into Florida. The NGF has been shown to be responsible for dramatic declines in native land snail populations in other parts of the world and is considered one of the world's worst invasive species. The goal of this study was to survey sites in both Everglades National Park (EVER) and Big Cypress National Preserve (BICY) for native tree snails and flatworms in sites ranging from high-use areas with abundant visitors and foot traffic to low use, less accessible or less frequently visited areas. Tree snails were surveyed during the day by meander surveys to determine presence/absence, followed by timed transects following meander survey success. Flatworms were surveyed at night, again by meander surveys to determine presence, followed by timed quadrat sampling. Flatworm specimens were genetically analyzed by Cytochrome Oxidase 1 (COI)COI barcoding to confirm species identification. A total of 5,855 observations of tree snails were recorded for three species of native tree snails, Orthalicus floridensis, Orthalicus reses, and Liguus facsiatus. Night surveys yielded 1,263 observations of flatworms (and one terrestrial nemertean species) representing 9 different species. Living tree snails, or evidence of their past occurrence in the form of shells, were found at most of the surveyed sites with suitable habitat. New Guinea Flatworm occurred more commonly at high-use sites than low use sites. The mean densities of NGF in EVER and BICY was 0.3 and 0.5 individuals per 5 m2. These NGF densities are low compared to NGF densities found in non-wilderness hammocks located in the highly populated Miami Rock Ridge area where the mean NGF density is 1.9 NGF per 5 m2, with a range of 0.2 to 8.2 NGF per 5 m2. These comparative results suggest that the invasion of NGF into EVER and BICY appears to be less severe than in more developed/urban areas. Several recommendations to limit the further spread of NGF in these protected areas are included in this report.