Reason for 'Disco' Clam's Underwater Light Show Discovered

Scientists have finally discovered the reasoning behind the "disco" clam's underwater light show, a new study describes.

When Nature World News first reported of this flashing mollusk, also known as the Ctenoides ales, lead author Lindsey Dougherty of the University of California, Berkeley thought that it used its spectacular display to attract prey (mostly plankton) or scare off predators. And now this latest study proves that she was right.

Dougherty's previous research set out to find the source of this two-inch mollusk's underwater disco dance. In crevices or small caves in Indo-Pacific coral reefs, it was thought that these invertebrates produced their flashing via bioluminescence within their tissues. But further investigation revealed that it was actually the result of the furling and unfurling of its highly reflective mantle lip.

Specialized tissues in its lips form a double layer, reflective to light on one side, but absorbent on the other. This unique mechanism and flashing lights is what gives this mollusk its nickname as the "disco" clam.

But why do they do this electric dance? To get to the bottom of the answer, Dougherty and her colleagues performed a series of experiments in the lab. First, using a powerful microscope they examined the structure and proteins in the tiny clam's eyes. It turns out their vision is too poor to use their flashing light to attract mates or other species, ruling out this theory.

Next, they tested the effect of the flashing on predators, which in the wild would include octopi, predatory snails, or mantis shrimp.

"In this case, the false predator was just a styrofoam lid. 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," Dougherty said in a statement.

The rate of their flashes also increased when phytoplankton were introduced to the tank, indicating that C. ales use the electric light is used to attract prey. The research team is still unsure of whether phytoplankton and others can even see this flashing, but they plan to conduct future studies to find the answer.

Dougherty presented this research at the 2015 annual conference of the Society of Integrative and Comparative Biology in West Palm Beach, Florida.

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