Throughout the tropical waters of the Indo-Pacific region, there’s a flashy mollusk that gives new meaning to the phrase “party animal.” Ctenoides ales, or the so-called disco clam, is a type of file clam famous for the flashing light show it puts on. Just last year, researchers discovered that this strobe light effect is not bioluminescence—light production through a chemical reaction—but instead is due to reflected ambient light.
Now, the same bunch of scientists believe that they have determined why these animals show off this electrifying display. According to the unpublished research, it is likely used to both warn predators and attract unsuspecting prey, but probably doesn’t attract other clams. The work was presented on January 4 at the 2015 annual conference of the Society for Integrative and Comparative Biology in Florida.
Creatures of the sea can be very glamorous. There are radiant jellyfish that light up the waters with fluorescent proteins, neon sharks that glow by emitting light at different wavelengths to those absorbed, and glittering clams that have lips like disco balls.
The latter, the aforementioned C. ales, produce light displays in an intriguing way. One side of their jazzy orange mantle lips, which are the folds used for feeding, are lined with tiny reflective spheres of silica, whereas the other side absorbs light. These microscopic beads reflect light, and the flashing effect is achieved by the animal rapidly rolling up and unfurling each side of the lip.
It is believed that this is the only species of bivalve (mollusks with a shell consisting of two hinged valves) to have evolved this particular type of light display. So why do they do it? Scientists had three different ideas: it could be used to lure prey, deter predators, or attract potential mates. To test these hypotheses, researchers from the University of California, Berkeley, collected some clams from Indonesia and studied them in an aquarium.
They found that, despite boasting 40 tiny eyes, their vision is inadequate to detect the flashing produced by other clams, suggesting it probably isn’t used for mating purposes. However, they did find that they ramped up their flash rate when potential “predators” (floating Styrofoam lids used to mimic threats) were added to the tank, with the animals almost doubling the number of flashes per second.
Furthermore, they found that the animals could be squirting out toxic sulfuric acid to deter predators, which would back up their “don’t eat me” signals. The animals had high levels of sulfur in their tentacles, and when the researchers added a substance that forms a precipitate in the presence of sulfuric acid, they found twice as much precipitate in the tank when the clams were disturbed than when they were left alone. Interestingly, when they added in a feisty mantis shrimp, the aggressive crustacean quickly recoiled after attempting an attack and went into a catatonic state, suggesting it could have tasted something noxious.
Lastly, the researchers found that the clams also increased their flashing rate when tasty plankton was added to the tank. Since some of these animals are known to be attracted to light, this suggests that the clams could be using their flashing display to attract prey.
Check out a video of them in action here: