Nestled in cracks and crevices in coral reefs off the Indonesian coast, so-called disco clams are busy putting on a light show. But unlike many animals in the ocean that produce their own light, a new study finds that these flashy mollusks catch and reflect ambient light for their displays.
Found throughout the Indo-Pacific, Ctenoides ales is a striking saltwater clam with colorful tendrils and a peculiar talent long known to divers: It produces flashes of light that at first glance look like flickers of neon or ripples of electricity. Hence its nickname, the “electric,” or disco, clam.
Lindsey Dougherty, a graduate student at the University of California at Berkeley, first encountered the clam during a dive in Indonesia and quickly became fascinated by it. So she decided to devote her PhD to figuring out how the disco clam produces its signature flash.
The animal’s impressive light show was long thought to be an example of bioluminescence—or an organism’s ability to produce light through chemical reactions—until research in the 1990s discovered it was actually a matter of scattering ambient light.
Dougherty and her team found that the flashing effect was due to the unique structure and composition of the clam’s fleshy lip. That lip, or mantle, contains two distinct tissue types that enable it to scatter ambient light, the researchers reported this week in the Journal of the Royal Society Interface.
The mantle edge is filled on one side with nano-size spheres made of silica, said Dougherty. “Silica is very rarely used by animals but has a high refractive index, which makes it a great reflector.”
The mantle’s other side is very good at absorbing light, resulting in the alternating, or flashing, light effect when the lips flap open and closed. Bivalves are filter feeders, so their shells are constantly opening and closing in order to let water pass over their gills to pick up food, explained Dougherty.
“The tissue furls and unfurls back and forth to expose the two distinct sides about twice a second,” she explained. When they’re startled—by a fake predator in a lab test, for example—”their flash rate jumps up to four times a second,” she added. The researchers studied the phenomenon using high-speed video and other tools.
The key question now hanging in the air like a disco ball is why the clams do what they do. For her part Dougherty suspects the clam’s flashy display may serve a signaling function of some kind or may ward off predators. “We’re also testing to see if they use the light to lure in prey or to recruit one another to settle nearby for spawning purposes,” she said.
“It’s very fascinating to think about what factors led to the development of this flashing,” Dougherty said, since no other bivalve displays light in such a manner. “[Disco clams] are pretty unique.”