Big Snails, Small Pond
Two undergrads, one mission: to determine what manner of freshwater snail lurks in the University of Minnesota Duluth's (UMD) Rock Pond. Equipped with rain boots and a lofty cloth net, they waded into the shallows of the 2-acre pond on a crisp September day. Within seconds they were holding up the largest snail they had ever seen. In fact the shoals of Rock Pond were littered with these golf ball-sized mega-snails.
Soon thereafter, UMD biologists confirmed an uncomfortable truth that Doug Jensen, Minnesota Sea Grant's Aquatic Invasive Species Program Coordinator, noted in 2004 and again earlier this year. These were not one of Minnesota's three dozen or so native aquatic snails. They were invasive Chinese mystery snails, denizens of aquariums and now Rock Pond.
Almost ten years ago, the University dealt with repairs to a constructed outflow and an infestation of goldfish by draining the pond. At that time, the crew noticed the mystery snails but neither goldfish nor mystery snails seemed to remain after the pond was refilled.
Similar to many aquatic invasive species, when Chinese mystery snails are poured from aquariums into lakes, ponds, and rivers they can compete with native species for food and space. Like many of Minnesota's native freshwater snails, Chinese mystery snails feed on benthic algae. Mystery snails have been recorded in over 90 bodies of water in Minnesota alone.
Chinese mystery snails found their way to the West Coast of North America in 1892, and they don't seem to be planning to leave. They were originally shipped to California for the Asian live seafood market, and were discovered on the East Coast by 1915. Their spread is likely due to people releasing them from aquariums or by consumers who purchased them from live food markets. Fish, crayfish and turtles will eat them. Desiccation and chemicals don't necessarily kill them. Chinese mystery snails have a trap door they can close to avoid unfavorable environmental conditions, such as drying out or chemical treatments. They can survive up to nine weeks out of water but once they find a lake or stream, they are able to reproduce quickly, giving birth to live young. Once they establish themselves in a body of water, they are basically unmanageable.
The best strategy for keeping places like Rock Pond free of invasive species such as mystery snails is by preventing their spread. How? Do not release aquatic pets and plants into the environment. Check out the HabitattitudeTM website for alternatives to releasing unwanted aquarium and water garden species (www.habitattitude.net).
By Emily Kolodge