ShareThisIt sounds like something out of a cheap horror movie -- but this scare is real.
Non-native Asian clams are spreading rapidly across parts of Lake Tahoe, often accompanied by stringy mats of bright green algae, and posing a new threat to the world-renowned mountain lake.
So far the clams, which are about the size of a dime and have been found in concentrations of up to 3,000 per square meter, are concentrated in the lake's southeast corner. But if they spread more widely -- and some have recently turned up in Emerald Bay on the southwest side -- the ecological health of the lake may be in danger.
"It is fairly serious and definitely a cause for concern," said John Reuter, associate director of the University of California, Davis Tahoe Environmental Research Center. "If it gets around the whole lake, we're looking at a different lake."
The clams have been in Lake Tahoe for at least seven years, scientists say, and apparently arrived on the hull of a boat, or as fish bait. But it wasn't until this spring that they were discovered in such high concentrations between Zephyr Point and Elk Point on the Nevada side of the lake.
And in that area, at a place called Marla Bay, environmental and visual effects are already obvious.
Along the lake bottom, scientists have found the Asian clam is out-competing the native pea clams. In some places, the Asian invaders comprise almost half of the sediment-dwelling organisms, according to a new annual survey of the lake's health released Tuesday by the UC Davis research center.
What's more, Asians clams excrete nitrogen and phosphorus, which Reuter said are appear to be promoting large "nuisance blooms" of bright-green algae that hug the bottom like shag rugs. When the algae dies, it is washing up on the beach, along with thousands of crunchy, sharp-edged clam shells, changing the nature of a walk along the Tahoe shore.
"The stuff is floating up on the beach; it's not quite like the ocean after a huge storm -- but again, even a bit is not the desired condition" that scientists and the public want to see at the lake, Reuter said.
Another concern is that this invasion may beget future ones. As the Asian clams die, they will decompose and release calcium into the lake, Reuter said. That calcium is something that the even more widely feared quagga mussels or zebra mussels -- which have not been found at Tahoe -- need to thrive.
Some limited efforts have been made to battle the invasion with suctioning equipment or bottom-hugging devices that starve the clams of oxygen. But more work needs to be undertaken to determine what works best.
"Some things have to be done very carefully because if you disturb the clam beds at the wrong time, you can make it worse," said Dennis Oliver, a spokesman with the Tahoe Regional Planning Agency.
But there is also a clear need to move quickly.
"The longer you wait, the worse it gets," Oliver said.
E-mail reporter Tom Knudson at tknudson(at)sacbee.com.
(Distributed by Scripps Howard News Service, www.scrippsnews.com.)
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