War on clams

War on clams has been declared at Lake Tahoe, a large freshwater lake in the Sierra Nevada Mountains of the United States. Scuba divers have been enrolled in a 400,000 USD project aiming to completely rid the lake of all Asian clams. The anti-clam endeavour is scheduled to begin in mid-March and is a combined effort by the governments of Nevada and California.

The Asian clam (Corbicula fluminea) is native to Asia and parts of Africa where it inhabits streams, canals and lakes. In this part of the world it is a natural part of the ecosystems and is even known as the prosperity clam or good luck clam. The Asian clam was introduced to North America in the 1920s by Asian immigrants for whom it was an appreciated source of food. It would however take until 2001 before the first specimens were encountered in Lake Tahoe. Since the first finding, the clam has been collected from numerous locations Tahoe’s southeast shore and authorities now fear that it will pave the way for even more dangerous invasive species such as the Ukrainian Quagga mussel (Dreissena rostriformis bugensis) and the Russian Zebra mussel (Dreissena polymorpha).

”We’re concerned they could create a positive settlement situation for the quagga mussels,” says Steve Chilton, aquatic invasive species coordinator for the U.S. Fish and Wildlife Service. ”We’re basically looking at all avenues through which the quagga mussel could get into the lake and eliminate that risk factor as much as possible.”

Steps so far have primarily focused on mandatory boat inspections to ensure no mussels are attached to them when they launch into the lake, but scuba divers participating in the new anti-clam project will actually be removing Asian clams from Lake Tahoe’s southeast shore. Starting in mid-March, divers will place plastic sheets, so called bottom barriers, over selected clam beds in order to deprive the clams of oxygen and nutrients. Divers will also carry out ”diver-assisted suction”, e.g. manually vacuum clams off the bottom of Tahoe.

”This needs to be done. We have to get our hands around the Asian clam problem,” Tahoe Regional Planning Agency spokesman Dennis Oliver told the Reno Gazette-Journal. ”We need to find out what works and what works best. Once we know that, we can develop a program.”

Invasive mussel species are known to form huge populations in environments where they lack natural predators and can for instance clog water intakes, attach themselves to boats and docks, and litter sandy beaches.

North America is not the only continent with an Asian mussel problem; Corbicula fluminea has begun to spread throughout Europe as well. It was found in the Rhine as early in the 1980s and then gradually found its way into the Danube through the Rhine-Maine-Danube Canal. In 1998 the first specimens were found in the Elbe and the species is now also present in the rivers of Portugal.