Since the introduction of fiber optic cables in the 1970s, they have become an essential component in various technologies such as medical devices and high-speed internet. Surprisingly, a specific type of marine mollusk has been utilizing similar mechanisms long before humans.
Since the introduction of fiber optic cables in the 1970s, they have become an essential component in various technologies such as medical devices and high-speed internet. Surprisingly, a specific type of marine mollusk has been utilizing similar mechanisms long before humans.
A recent study has shown that heart cockles, a type of clam recognized for their heart-shaped shells, possess special structures in their shells that function like fiber optic cables. These structures transmit specific wavelengths of light into the clams’ tissues.
Researchers from Duke University and Stanford University utilized electron and laser microscopy, along with computer simulations, to reveal that the shells of heart cockles contain transparent sections made up of extremely thin strands bundled together, enabling light to reach deep within the bivalves.
The research findings were published on November 19 in the journal Nature Communications.
Heart cockles are found in the warm waters of the Indo-Pacific region and have a mutually beneficial relationship with tiny algae that reside within their tissues, which rely on light for growth.
While the algae enjoy protection and a secure environment, the clams benefit from the sugars produced by the algae through photosynthesis.
To sustain this partnership, heart cockles have developed sophisticated methods to harness light, ensuring it reaches their otherwise dark interiors.
They have evolved natural “skylights” within their shells, allowing them to nourish their algal companions without having to open their shells and risk exposure to predators.
“They essentially evolved translucent windows in their shells,” said Dakota McCoy, the lead author of the study, who began this research as an NSF PRFB Fellow under the guidance of Sönke Johnsen at Duke. McCoy is now an assistant professor at the University of Chicago.
By employing a laser scanning microscope to analyze the 3D structure of heart cockle shells, the researchers found that beneath each translucent window were tiny bumps, smaller than grains of sand, that worked like lenses to concentrate sunlight into a beam that reaches the clams’ interior where the algae live.
“I imagine it like some organic cathedral with stained glass windows, with the light falling on the parishioners inside,” remarked Johnsen, the senior author and a biology professor at Duke.
The researchers were taken aback when they examined the shells under a scanning electron microscope.
Heart cockles, along with many marine creatures, use a unique form of calcium carbonate known as aragonite to construct their shells. Under microscopic observation, the majority of a heart cockle’s shell exhibits a layered pattern, with thin aragonite plates aligned in various orientations, which resembles intricate brickwork, as described by McCoy.
However, within each window, the shell forms tightly capped, hair-like fibers instead of plates, all aligned toward incoming light.
“It looks just completely different than what you’d expect,” McCoy commented.
Computer simulations indicated that the size, shape, and orientation of these fibers are optimal for channeling more light into the heart cockles’ interior compared to other potential design variations.
In particular, these structures allow light in the blue and red spectrum—ideal for photosynthesis—while preventing harmful ultraviolet radiation from entering their shells, which could potentially harm their DNA.
“Together, the fibers and the lenses create a system for filtering out harmful wavelengths, channeling in beneficial ones, and focusing that light deeply enough so that the algal partners receive the most favorable lighting conditions,” Johnsen explained.
The researchers also discovered that because the bundled fibers in the shells are so tiny and tightly packed, shining a light through them produces a high-resolution image of whatever is beneath, similar to a TV screen.
The team noted that further research is necessary to determine whether the heart cockles utilize this image projection capability in any way.
It’s possible that one day, these clams could inspire innovative designs for fiber optic cables that facilitate long-distance light travel even around curves, without signal loss, said Johnsen.
“The shells perform a remarkable function,” McCoy stated.
This research received funding from the National Science Foundation (grants 2109465, 1933624, and ECCS-2026822).
