Sea Sapphire

From sea to shining sea... but they didn't expect it to shine like this!

I've been wondering what this thing was for quite a while now and thanks to RR Helm at Deep Sea News, I finally know. At last!

It's a Sea Sapphire, a Copepod just a few millimetres long which belongs to the genus Sapphirina. Copepods are those tiny crustaceans who drift on the currents and, through sheer weight of numbers, become a significant part of the diet of such giant filter feeders as the Whale Shark and the Manta Ray.

Image: JesseClaggett
Female with sacks of eggs

Female Sea Sapphires are parasites of Salps, those strange tube-of-gelatin creatures that happen to be more closely related to vertebrates than most jelly-creatures. We've seen how some parasitic Copepods become horribly misshapen into ghastly, nightmarish forms as they adapt to their dastardly lifestyle, but Sea Sapphires appear mercifully unaffected.

Video: liquidguru

It's only the males who sparkle and they're free-swimming so they can travel around to show it off. You wouldn't think it to look at them, but they're almost completely transparent! Their startling sparkling isn't a result of luminescence, either. Rather it's a fine example of structural colouration, where colour comes from light interacting with the physical structure of a surface.

Sea Sapphires are covered in layers of tiny crystals that only reflect light within a narrow range of wavelengths. In this case, the blue bit! It means they glisten with wonderful iridescence when light strikes them from a certain angle, and all but disappear when viewed from another angle.

Different species reflect different colours. Coupled with their well-developed eyes and it seems likely their beautiful glow is a beacon of love by which amorous Copepods seek out their sweethearts in the vast seas. Perhaps a crystal-lit dinner is on the cards?