Scientists say they've figured out the secret of a marine bivalve so adept at creating a vivid light show it's been dubbed the "disco clam."
Researchers from Australia and the United States used a number of imaging techniques to discover the how the species Ctenoides ales creates its rhythmic displays of a purple light, and it's all down to microscopic silica spheres or beads located around the edges of the clam's "lips," or mantle fold.
For many years scientists had thought the clam's light display was the fairly common marine phenomenon known as bioluminescence, light-producing reactions of chemicals.
But in reporting their research in the Journal of the Royal Society Interface, the scientists say rather than producing light the clams are simply reflecting it.
By curling and then uncurling tissue lining the lips of it two shells, the disco clam can alternately expose the reflecting silica beads and a light-absorbing, nonreflective tissue.
The silica -- the main element found in quartz and glass -- reflects between 85 percent and 90 percent of the light that hits it underwater, the researchers found.
"They're almost ideal reflectors in blue-green water environments," says Lindsay Dougherty, a doctoral student at the University of California, Berkeley.
The silica beads are a perfect size for the most effective scattering of light, the researchers determined in studying the clam both in the laboratory and in its natural habitat.
The clams, found in waters from 10 to 160 feet deep off Indonesia and Australia, can "flash" their light show by quickly rolling and then unrolling the edges of their shell mantles at around 2 times a second, high-speed cameras have revealed.
As to the purpose of all the "disco" activity, Dougherty says it could be to attract mates or lure prey to come closer.
It might also be to frighten off predators, something suggested by a finding by the researchers that when they moved objects closer to one of the clams, the rate at which it flashed it light show almost doubled, a possible "no trespassing" sign.
The element silica is fairly rare in the world's oceans, Dougherty said, making the fact that the disco clam has evolved to make use of it all the more intriguing.
"To the best of our knowledge, C. ales is the first animal to use silica as a scattering structure via intracellular nanospheres," she says. "Indeed, it is unusual to see silica secreted by animals for any purpose."
