Buzz
Wikimedia Commons
At first glance, Ctenoides ales is clearly no ordinary bivalve you'd toss into a soup. This vibrant reddish-orange mollusk thrives in the nooks and crannies of Indo-Pacific coral reefs, producing dazzling light displays visible even in natural light—earning it the nickname 'disco clam.' Initially, scientists speculated that the flashing might result from bioluminescence, a chemical process that generates light within an organism. However, recent studies by Lindsey Dougherty from the University of California, Berkeley, alongside researchers from Duke University and the University of Queensland, Brisbane, Australia, reveal a more intricate mechanism at play.
Dougherty employed advanced tools—such as a transmission electron microscope, spectrometer, energy dispersive x-ray spectroscope, and high-speed video—to analyze the clam's mantle lip. She discovered that the flashes aren't caused by bioluminescence but by a unique double-layered tissue structure. The inner layer of the clam's lip contains silica spheres that reflect light like a mirror (or a disco ball!), while the outer layer absorbs light. By rapidly rolling and unrolling these tissues—typically twice per second—the clam creates the illusion of flashing. This adaptation appears unique to disco clams, raising the question: what purpose does it serve?
Dougherty and her team explored several theories for the clams' flashing behavior. Microscopic analysis of their 40 tiny eyes suggested their vision is too poor to detect flashes from other clams, eliminating the possibility of mate attraction. "We found little evidence of chemical or visual attraction between clams, and their eyes likely can't perceive each other's flashes," Dougherty explained to LiveScience. However, two other hypotheses showed potential: the flashes might lure prey or deter predators.
To evaluate the prey hypothesis, researchers introduced phytoplankton into the lab tank. Upon detecting the prey, the clams significantly increased their flashing. While some plankton are drawn to light, it remains uncertain if this applies to the disco clam's prey. Further field studies are planned to explore this phenomenon.
The disco clam's natural enemies include octopuses, mantis shrimp, and certain snail species. To test the predator hypothesis, scientists initially used a styrofoam lid, simulating a looming predator. The clams responded by accelerating their flashing from 1.5 to 2.5 times per second when the lid approached.
In a subsequent experiment, a real predator was introduced: Odontodactylus scyllarus, the peacock or harlequin mantis shrimp, known for its powerful claws capable of delivering 160 pounds of force to crack open prey. The shrimp attacked the clam multiple times but eventually retreated and appeared to enter a catatonic state, followed by unusual behavior toward the mollusk. "It's highly unusual for such aggressive creatures to avoid attacking a flashing clam," Dougherty explained to LiveScience. "This behavior is quite perplexing."
Both experiments revealed elevated sulfur levels in the water, leading Dougherty to hypothesize that the clams might secrete an acidic mucus from their tentacles to deter predators. "Flashing to signal 'I'm unappetizing' is one thing, but you need to substantiate it," she noted.
