Invading clams in chilly Tahoe slow to reproduce | TahoeDailyTribune.com

Invading clams in chilly Tahoe slow to reproduce

JEFF DeLONG
Reno Gazette-Journal
The Asian clam, several of which are seen here in this June 20, 1994 photo, after they were taken from San Francisco Bay, is one of about 240 aquatic alien species that thrive in the Bay Area and delta. (AP Photo/San Francisco Estuary Institute, Andrew N. Cohen)
ASSOCIATED PRESS | SAN FRANCISCO ESTUARY INSTITUTE

RENO, Nev. (AP) – When it comes to invading clams, Lake Tahoe might not be a very good place to make babies.

That’s the encouraging conclusion of new research by scientists at the University of Nevada, Reno who found that cold temperatures and lack of food combine to discourage reproduction of Asian clams in the lake.

“This could be good news. It really could be,” said Sudeep Chandra, a UNR researcher specializing in freshwater science.

“The fact is Lake Tahoe has a few things going for it when it comes to this invasive species spreading around,” Chandra said.

Diminished ability to reproduce could mean that efforts to manage clam populations – including killing them by covering clam beds with rubber mats – have a better chance at long-term success, Chandra said.

“The question is, at what rate do they grow? If they are outgrowing what you manage, the problem will keep coming back,” Chandra said.

Asian clams, first established in the Columbia River Basin in the 1930s and discovered in the lower Truckee River in 1981, were identified in Lake Tahoe for the first time in 2002. Tahoe is the highest-elevation lake they’ve ever been found.

Asian clams have spread rapidly across the southeast corner of Lake Tahoe over the past nine years and have also turned up in a football-field-sized patch in landmark Emerald Bay.

The clams have been linked to noxious algae blooms, and scientists fear they could lead to successful establishment of other, potentially worse invaders – quagga or zebra mussels. The clams could help that happen by changing water chemistry and providing a stable platform to which mussels can adhere.

That scenario, Chandra said, would equate to an “invasion meltdown” at the landmark alpine lake, and could have decimating consequences to Tahoe’s ecology and economy.

“We’ve spent over a billion dollars to try to protect the clarity of that lake,” Chandra said. “A single species could unravel that.”

Research headed by UNR doctoral student Marianne Denton was designed to test the theory that Tahoe’s Asian clams will grow in the same exponential manner as in other water bodies.

Instead, Denton found that limited food availability and cold water temperatures that shorten the reproductive period to mostly August and September significantly reduce reproductive potential of Tahoe’s clams. In other water bodies, reproduction occurs throughout the summer into early fall.

“Lake Tahoe’s clams are different,” Denton said. “I think Lake Tahoe’s reproductive rate is very low.”

Another promising find was a lack of juvenile clams in deeper waters. While the densest populations are found in depths of about 15 feet, adult clams also are found as deep as 200 feet.

Scientists suspect those clams were carried into deep water by waves or currents, and while they survive there, colder water temperatures make reproduction impossible.

That’s important because attempting to control clam populations in the deep is particularly difficult, Chandra said.

“That means we don’t have to worry much about managing deep water populations,” Chandra said. “The colder water temperature means they don’t get the chance to spawn.”

While controlling the spread of Tahoe’s Asian clams will remain a major challenge, evidence of their limited reproduction potential is encouraging at a time Tahoe faces threats from a number of invading species, Chandra said.

In addition to the clams that exist in the lake and the mussels that threaten to arrive, the lake’s ecology is also threatened by invasive weeds and warm water fish, such as largemouth bass and bluegill. Another non-native fish that is particularly worrisome, smallmouth bass, was recently discovered in the lake.

“Tahoe is being invaded from all fronts,” Chandra said.

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Information from: Reno Gazette-Journal, http://www.rgj.com


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