Long a problem in the western U.S., the New Zealand mud snail currently inhabits four of the five Great Lakes and is spreading into rivers and tributaries, according to a Penn State team of researchers. These tiny creatures out-compete native snails and insects, but are not good fish food replacements for the native species.
"These snails have an operculum, a door that closes the shell," says Edward P. Levri, associate professor of biology at Penn State's Altoona Campus. "They can be out of the water for longer than other snails and when fed to fish, they are not digested and sometimes come out alive. This has a potential to alter the salmon and trout fisheries because they alter the food chain."
The New Zealand mud snail grows to a maximum of a quarter of an inch and is more normally a sixteenth to an eighth of an inch in length. The hard shell is capable of sealing off the soft animal from outside influences. In New Zealand, the snails reproduce asexually, resulting in identical clones, or sexually. However, in invaded areas, asexual cloning is the only mode of reproduction.
This mud snail spread to England as early as 1850 and Europe in the late 1800s. It is found in Japan, but when the snail arrived there is unknown. The first mud snail found in the U.S. was in 1987 in the Snake River, Idaho, but the species did not appear in the east until 1991 in Lake Ontario. The western and eastern U.S. populations are separate episodes of introduction, because they represent different clones; in each case, only one snail needed to be introduced to begin the invasion. The snails in the Great Lakes region appear to be the same as one clone found in Europe.
"In the western U.S., this species is of special concern largely because of their ability to modify ecosystems," Levri told attendees today (Aug. 8) at the Ecological Society of America's annual meeting in Milwaukee.
The snails in western streams alter the nitrogen and carbon c
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