Crafty clams use fiber optics to score sugary meals

When it comes to technologies used only by humans, you might think that fiber optics would rank right up there. Such is apparently not the case, however, as scientists have discovered that a certain clam uses "fiber optics" of its own to get food.

Named for its heart-shaped shell, the heart cockle is a marine clam found in the Indo-Pacific region.

Along with plankton that it filters from the water, the mollusk also feeds on sugars produced by algae that live in its soft tissue. The algae produce those sugars via photosynthesis, which requires sunlight … and there typically isn't a whole lot of sunlight deep inside a sealed-up clamshell.

While the cockles could give the algae some light by periodically opening their shells, doing so would leave their tender insides vulnerable to predators. Instead, they have evolved translucent windows that take the form of a series of small bumps in their shells. In a recent study involving scientists from Duke and Stanford universities, those windows were examined via electron and laser microscopy.

It was found that beneath each window, which serves as a sunlight-focusing lens, the layered calcium carbonate plates that make up the shell form into tightly packed bundles of hair-like fibers. And whereas the regular plates run lengthwise through the shell, like stacked bricks in a brick wall, the fibers run perpendicular to them, going through the thickness of the shell.

Not only do these fibers carry sunlight from the surface of the shell down to the algae, but they also filter out the ultraviolet segment of that light – which could be harmful to the clam – while allowing through the blue and red light that the algae require for photosynthesis.

"Together, the fibers and the lenses create a system for filtering out bad wavelengths, channeling in the good wavelengths, and focusing so that they go far enough into the shell, so that the algal symbionts get the best lighting environment possible," said Duke's Prof. Sönke Johnsen, who led the study along with Stanford postdoctoral researcher Dakota McCoy.

A paper on the research was recently published in the journal Nature Communications.

Source: Duke University