A piece of the algae, left. A close-up look, right, reveals its glittery internal structure.
Photo: Lopez-Garcia et al, Science Advances (2018)

There’s a reason that many natural things look unbelievably cool: Evolution. Given the stresses of existing on this turbulent spinning orb, some organisms must adapt in literally dazzling ways. Like this alga, which is basically a living opal.

This confused me at first, too, but the Cystoseira tamariscifolia algae has an iridescent shimmer just like an opal crystal does. A team of British scientists looked at it under a microscope, and found that it’s all physics. The plant has light-controlling crystals inside its cells to help with photosynthesis.

“We have living jewels in the environment,” study author Heather Whitney from the University of Bristol in the United Kingdom told Gizmodo. “It’s a Fabergé seaweed.”

C. tamariscifolia is a common brown alga found in Europe and the Mediterranean. Looking at it under a microscope reveals a shimmering iridescence. An even closer analysis reveals two to three fat-filled vesicles in each of its cells, according to the paper published last week in Science Advances. 

Inside these sacs, lots of spherical fat globules arrange themselves into a three-dimensional lattice, similar to the lattice structure that silicon dioxide takes in opals, to give the alga its special iridescent property. Not only that, but it appears that the algae can choose to order and disorder the spheres to control how light is scattered (or not) inside cells.

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It makes sense that such a plant would do this, explained Whitney. C. tamariscifolia inhabits coastal areas. At any given time, it could be underwater or in the intense sun on the sand. She hypothesizes that the different arrangements could help the algae direct incoming light into its chloroplasts, where photosynthesis takes place, when the algae is underwater, or transmit the light away from the chloroplasts in bright sunlight to protect the chloroplasts from overexposure.

She also thought that a human-made version of this natural design could be useful in engineering. It wouldn’t be the first time we’ve seen weird, light-manipulating inventions inspired by nature.

And who knows, maybe there are even more plants with strange optical properties. Said Whitney: “This is the tip of the iceberg.”

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[Science Advances]