ASK MR. SUN:

How did seashells get to the former town of St. Thomas?

Asian clam shells dot the site of the lost town of St. Thomas. The clam, an invasive species, arrived during the 1960s.

Las Vegas Sun

Tuesday, July 7, 2009 | 2 a.m.

Ask Mr. Sun

Dry Town, Dry Future

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For 60 years, the town of St. Thomas lay beneath the waters of Lake Mead. In 2002, St. Thomas re-emerged from the shrinking lake and scientists don't expect the site to ever be under water again. St. Thomas's appearance offers further evidence of the Southwest's critical water problem. Lake Mead is one of the largest reservoirs in the world and one of the most important water sources in the western United States, however, over the past few years scarce rain and snow amounts have lowered the lake's water levels significantly. According to researchers at Scripps Institution of Oceanography, there is a 50 percent chance Lake Mead will be dry by 2021 if climate changes continue as expected and future water usage is not curtailed.

Lost and found

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The shells are the carcasses of Asian clams abandoned by the retreating lake.

No one knows exactly how the freshwater bivalve mollusks, which are native to southern and eastern Asia and Africa, got here. But experts say they arrived in the 1960s and their best guess is they were unintentionally transported here by boaters.

They were first spotted in U.S. waterways nearly 100 years ago and have been spreading ever since.

Although the clams are undoubtedly an invasive species, they rank below the newly arrived quagga and zebra mussels on the Lake Mead Most Wanted list.

The Asian clam “isn’t as destructive as the quagga and zebra mussels since it doesn’t attach itself to boats and in-water infrastructure,” Lake Mead National Recreation Area spokesman Andrew Munoz said in an e-mail.