Understanding the sea sapphire’s shimmery invisibility cloak could open the way to a new generation of optics.
Sea sapphires are tiny crustaceans that belong to the Sapphirina genus of copepods. The males of some species are shimmery, and even have the ability to seemingly disappear from plain sight.
Now, scientists have uncovered how these tiny sea dwellers shine in and out of visibility. Researchers at the Weizmann Institute and the Interuniversity Institute for Marine Sciences in Israel measured the light reflectance of live Sapphirina, and then studied the structure of their shells.
Sapphirina’s shells are covered with a layer of chitin, and just below that are layers of extremely regular crystals—which reflect light. The researchers describe them as “a continuous mosaic surface of closely packed hexagonal crystals,” and resemble something a bit like floor tiles. Layers of these thin crystals are separated by cytoplasm—a gel-like substance. It turns out that the varying thickness of this cytoplasm layer is responsible for the different colors that flash off of the Sapphirina’s body.
The angle of the light reflecting off of the crystal layers also changes how the animal looks. For one species of Sapphirina, a 30 degree tilt makes the light reflect a deep violet color, and at a 45 degree tilt the animal becomes nearly invisible. This is because the reflectance passes out of the visible light range and into the invisible ultraviolet range.
In the video below, you can watch a sea sapphire shimmer in and out of visibility:
Sea sapphires tend to swim in spirals, which causes them to change their tilt in relation to the light in their environment. Researchers think this may help them communicate, and may also be a defense system for avoiding predators.
This research not only helps biologists better understand a little-know sea creature, but it could also inspire new optical technologies.
These findings are published in the Journal of the American Chemical Society.