Scientists are declaring war on Asian clams in Lake Tahoe, where the little mollusk is causing big problems for the iconic tourist destination.
In what's possibly the largest Asian clam control project in the nation, divers will place thin rubber mats on about 5 acres of infested lake floor at the mouth of Emerald Bay, in an effort to smother the fast-growing clams.
Biologists and students gathered Tuesday at UC Davis to prepare the rubber pond liner material, rolling it out and reinforcing it with steel rods. Divers are expected to begin installing the mats Monday, 16 feet underwater on a gravel sill that separates the bay from Lake Tahoe.
Billions of the fingertip-sized Asian clams, a non-native species, are creating clouds of stringy algae in the lake water, leaving behind sharp-edged shells on the beach, messing with water quality and muscling out native species for food and habitat.
While other areas of Lake Tahoe are more heavily infested, Emerald Bay is in the early stages of invasion, with clam numbers small enough to manage.
"This is an experiment to see if we can hit these isolated satellite populations of clams," said Geoffrey Schladow, director of the UC Davis Tahoe Environmental Research Center, a partner on the project. "We chose Emerald Bay because it's a state park, it's a pristine bay, and one of the most photographed landmarks in the world."
Divers will drag 10-foot-by-100-foot sections of rubber sheeting underwater and install them by hand.
The $810,000 project, funded and supported by about 10 public and private agencies, will take from four to six weeks to lay the material. It will stay in place for a year, which is expected to wipe out the clams in that section of the bay.
Officials have alerted boaters to expect delays when entering Emerald Bay during installation.
Schladow said Asian clams have been multiplying in American waterways for about a century, but were first noticed in Lake Tahoe about nine years ago, possibly hitchhiking from a recreational boat or dumped from a home aquarium. Four years ago, the lake's Asian clam population "exploded," Schladow said.
In Emerald Bay, the population is estimated at about 50 clams per square yard, while parts of the lake are infested with 6,000 to 7,000 clams per square yard.
The clams' waste acts like fertilizer on the natural algae in the lake, spurring growth and clouding the water, Schladow said. The increase in algae changes the water color and chemistry, even affecting the taste as it's piped into drinking water systems, he said.
The infestation also washes up dead and rotting clams and shells onto the beach, which has drawn complaints from residents and tourists, said Kristi Boosman, a spokeswoman with the Tahoe Regional Planning Agency.
The clams' most significant impact, however, is disturbing the food web of the lake, either curtailing or boosting populations of other plants and animals, Schladow said.
The rubber mats will cut off oxygen to the clams. The mats will have a layer of aspen tree strands, and as the organic material decomposes, it robs the clams of more oxygen, Schladow said.
The technique was successfully tested on a pair of half-acre plots in the southeastern portion of the lake in 2010, Schladow said, and may be used more extensively in the lake in the future. It also has been adopted by officials to control Asian clams in Lake George in New York, he said.
Scientists will take sediment samples over the next year, monitoring nutrient and oxygen levels under the mats, and tracking the effects on the Asian clams.
Without treatment, Asian clam populations can escalate quickly and be expensive to manage, said Patty Kouyoumdjian, executive officer of the Lahontan Water Board. She said the board has laid out $789,000 since 2009 to control the Asian clam infestation in the lake.
"Invasive species are a real threat to Lake Tahoe and its near shore environment," she said.