U.S. Department of the Interior
U.S. Geological Survey
OFR 2010-1126

Melanoides tuberculatus (fig. 1), a gastropod that is not native to South Florida, was identified in Biscayne National Park (BNP) while researchers from the U.S. Geological Survey were conducting other studies around the Black Point canals in the summer of 2003. A study to determine the distribution, genetics, and salinity tolerance of this freshwater species began in 2004. For park managers and the recreational users of BNP, the presence of Melanoides tuberculatus is cause for concern because it is the intermediate host for several trematode parasites that affect humans and animals in multiple ways:

1. Human health concerns include parasites (trematode worms) that affect the lung (Paragonimus westermani) and the liver (Clonorchis sinensis, and Opisthorchis sp.). Skin irritations and lesions can also be caused by trematodes that normally infect other species.
2. Animal health concerns include parasites that affect the eyes of waterfowl (Philophthalmus megalurus), a trematode that burrows into the cartilage of fish and can lead to death (Centrocestus formosanus), and a trematode that infects the muscle tissue of fish and causes multiple abnormalities (Haplorchis sp.). When parasite-infected fish or crustaceans are eaten by birds or mammals, the next stage of the life cycle is in place (fig. 2).
3. Native snail species concerns include the potential displacement of invertebrate species that make up the natural nearshore benthic communities in BNP. M. tuberculatus has very high reproductive rates, reproduces via parthenogenesis, and is live bearing, factors which increase the survivability of the offspring and increase competition for limited resources.

These snails are considered to be freshwater animals in their native habitat of Southeast Asia. However, they have been collected in BNP in both estuarine and marine waters along the western margins of BNP and, as far as 1.7 kilometers (km) from shore at the Black Point canal inflow into Biscayne Bay (383 live per square meter (/m²). In BNP, M. tuberculatus is a benthic inhabitant grazing on micro algal components at the sediment surface. A documented population with as many as 23,000/m² was observed at Snapper Creek, near Coral Gables, FL (Roessler and others, 1977), north of BNP.

Figure 1. Melanoides tuberculatus samples collected from Biscayne National Park, FL. The two top images are live specimens used in the salinity resilience experiments. The two bottom images are pristine debris, adults (left) and juveniles (right) collected from BNP. [larger image]

Figure 2. Life cycle of parasites that utilize Melanoides tuberculatus as an intermediate host. Note the multiple vectors in the metacercaria and adult stages (From Wingard and others, 2008). [larger image]