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‘Disco clams’ use their groovy flashing lights to fight off predators

University of California at Berkeley researcher Lindsey Dougherty discovered the source of the disco clams' rhythmic light show. (Video: University of California at Berkeley)

Disco clams give a super funky little light display, but it might not be to attract attention — in fact, disco clams might use their flashy light show when they want to be left alone. Unlike most animals that light up, these creatures of the tropical Pacific don't use bio-luminescence. Instead of using a chemical reaction to produce light, they act like their namesakes — disco balls.

A few months ago, University of California Berkeley grad student Lindsey Dougherty figured out the real mechanism. Now she may have figured out why these funky little clams boogie in the first place.

In June, Dougherty — who's been fascinated with the two-inch clams since she first saw them on a dive in Indonesia four years ago — published her initial research on Ctenoides ales in the Journal of the Royal Society InterfaceShe found that disco clams had lips packed with tiny balls of silica, which makes for a very reflective surface.

The clams reveal these reflective bits by furling and unfurling their lips, making for a rippling light effect. The shiny spheres are especially good at reflecting blue light, which is more likely to penetrate to 10 to 150 feet below the surface, where the clams dwell.

Now Dougherty believes she may have found out why the clams put on such a show, and explains it in a new, as-yet-unpublished study presented Jan. 4 at the 2015 annual conference of the Society for Integrative and Comparative Biology.

First of all, this ritzy display isn't for mating. Disco clams may have around 40 little eyes, but their eyesight just isn't good enough to see the light shows of their own species. Which is kind of a bummer, because if I was walking around with my own personal rave, I'd want to be able to enjoy it.

So it's not surprising that the clams, when studied, flashed often in the presence of prey: Just like shiny fishing lures might catch a tuna, the clams' glimmering lights may prove attractive to the plankton they eat.

But they also flashed more (jumping from around 1.5 flashes a second to 2.5) when researchers exposed them to a fake predator. In addition to the flashing lights, which may serve as a "keep away" to predators like the gaudy mantis shrimp (who coincidentally have amazing eyesight), the clams might also spew toxic snot — though more research is needed to prove the second bit.

So now we're pretty sure of how disco clams manage their flashing lights, and pretty sure of why they do it, too. Next, Dougherty will examine how disco clams got so funky to begin with.

It's possible that they get their little silica beads from the plankton they eat, which would make for a fascinating symbiotic relationship — where the clams' prey was attracted by the remains of their own kin.

Or maybe they just come from sand. But even if these clams are just chewing on the sea bed, they're still pretty cool.