Gluttonous Snails Threaten Farms and Ecosystems
Aquarium enthusiasts have often marvelled at the voracious and undiscriminating appetites of their pet apple snails. Lately, the South American molluscs have emerged from their glass-walled confines and settled into the smorgasbord of wetlands across the southern United States.
Scientists recently examined the genetic code of exotic apples snails in the US to determine the species, their origins and their potential for ecological and economic damage. Of the five species encountered, three have scientists worried.
Two of the invasive creatures are channeled apple snails native to marshes and rivers near Buenos Aires, Argentina. Golden apple snail, Pomacea canaliculata, first showed up in Lake Miramar near San Diego in 1997. It now also lives in Arizona and may have just arrived in northern Florida. This species could eventually range as far north as San Francisco.
A close relative, Pomacea insularum is spreading rapidly into American wetlands. It first appeared in Houston, Texas in 1989 and has since moved into the surrounding counties. In 2005 the snail was discovered in Georgia's Alabaha River. But Florida is where this snail is really becoming prevalent, particularly between Tampa and Orlando, near Jacksonville and Tallahassee, and in the Everglades National Park. Other potential apple snail habitat exists in Mississippi, Louisiana, Alabama and South Carolina.
A third invasive species, spike-topped apple snail, Pomacea diffusa originates from Belem, Brazil. It has survived in Florida wetlands since the mid 1960s, and by 2003 had arrived in Mobile, Alabama.
Apple snails are huge, some growing well over five centimetres (two inches) across. The big eaters devour many types of aquatic plants, gobble eggs of fish and invertebrates, and even scavenge animal carcasses.
The consequences of these exotic snails moving into natural aquatic ecosystems are manifold. The snails have already demonstrated their destructive potential after being introduced to Southeast Asia. Their appetites could decimate local animal and plant populations. They'll also directly compete for food with native fish, shrimp and crayfish.
The snails especially pose a threat to wetland rice farms in California, Texas and other southern states. Farmers in Thailand and elsewhere in Southeast Asia struggle to keep golden apple snails from destroying rice seedlings.
Timothy A. Rawlings, Kenneth A. Hayes, Robert H. Cowie and Timothy M. Collins. 2007. The identity, distribution, and impacts of non-native apple snails in the continental United States. BMC Evolutionary Biology. 7: 97.