Clams Go Disco and Light It Up.
While not normally thought of as a club hopping creature capable of glowing in the dark and poisoning predators, the “disco clam” or Ctenoides ales as it is formally known, has been impressing researchers with its ability to light up the sea floor.
A team of researchers from the University of California-Berkley presented their findings on January 4th at the 2015 annual conference of the Society for Integrative and Comparative Biology in West Palm Beach, Florida. Team lead, Lindsey Dougherty, a doctoral candidate of marine biology at UC Berkley first encountered the flashy clams in a dark, underwater cave during a dive in Indonesia.
“It was on that trip I first saw the disco clam, and immediately fell in love,” reminisced Dougherty in a press release. Dougherty and her team members Professor Roy Caldwell and undergraduate Alexandria Neibergall brought some of these clams back to the lab to see if they could discover why they flashed and what mechanism in the clams’ anatomy caused the underwater light show.
Researchers first looked at the lips of the clam as they furled and unfurled. They found that these lips are double-sided with one side reflecting light and the other absorbing it. When the clam moved its lips, the combination of the reflection and absorption gave the appearance of flashing light. Even the dim blue light of the cave where Dougherty first found the species, was enough to create the flashing effect.
Having discovered how the clam flashed, the next task was to determine why. The team examined the eyes; forty tiny peepers on each clam, and found that they lacked the structure and proteins to provide vision sharp enough to clearly see other creatures. Since the strobe light quality of the disco clam could not be used to attract other clams, the focus changed to protection.
To mimic the approach of a predator, researchers placed an object into the tank with the clams. “In this case, the false predator was just a styrofoam lid,” Dougherty said. “But it turns out a styrofoam lid is indeed pretty scary to the clams, because their flash rate almost doubled from just under 2 Hz to just under 4 Hz.” The increase in flashes also occurred when a food source was nearby, in this case phytoplankton, which are naturally attracted to light.
The next step was to see how the clams would respond to an actual predator. In its natural habitat, the clams are preyed on by the neighborhood tough guy, the peacock mantis shrimp. Normally these shrimp could crack open a clam and have a meal in about 45 minutes. However, researchers noted that only a few minutes after beginning its attack on the clam, the shrimp recoiled and became catatonic. It seems that in addition to scary flashing lights, when attacked the clams secret toxic snot that contains high levels of sulphuric acid.
“If you’re flashing and saying, ‘I’m distasteful; don’t eat me,’ that’s one thing, but you have to sort of back it up,” Dougherty said and the acid did the job nicely. The team plans to go to Indonesia to further study the clams’ eating habits, since that is difficult to replicate in the lab environment. While those in the hobby trade of aquariums and tropical fish were always aware of the furiously flashing mollusk, no one really understood why or how the clam put on the light show until the team from UC Berkley started looking into the phenomenon. At present, the disco clam is the only clam with this particular anatomy and behavior. The team hopes to uncover more information when they observe the natural habitat.