Nearly 2-Meter Glow-In-The-Dark Shark Is Largest Known Luminous Vertebrate Yet

If you ever find yourself lost in the Twilight Zone, don't go towards the light. Image credit: Jerome Mallefet et al 2021.

If you’ve been keeping up to date with our Plants & Animals feed of late you might have picked up on lots of animals joining the “glow in the dark” club. From Africa's springhares to Australia’s marsupials and even a web-footed gecko, the natural world seems to be basking in its unique glow. There’s three new contenders in town, however, and one is the largest glowing vertebrate known to science.

The sparkly specimen in question is the kitefin shark, which alongside two other deep-sea sharks has been found to glow under ultraviolet (UV) light. Bioluminescence is by no means in short supply in the deep ocean. Everything from shrimp to jellyfish and salps are rocking the glow-up and the ability to light up appears to play a greater role in deep-sea ecosystems than first thought. Light is a big deal for these animals that occupy what's known as the Twilight Zone in the water column, spanning from just below 200 meters to 1,000 meters (650 to 3,280 feet) deep. The interface sits between the sunlit species above, which science knows a lot about, and the mysterious creatures of the deep, which we are far less clued up on.

Published in the journal Frontiers in Marine Science, the three species identified include the kitefin shark (Dalatias licha), the blackbelly lanternshark (Etmopterus lucifer), and the southern lanternshark (Etmopterus granulosus) with all specimens coming from the Chatham Rise, off the coast of New Zealand. Researchers photographed the sharks under UV light to compare their luminescence against each other and combined this information with samples taken from the sharks’ light organs where light is created through a chemical reaction.

Growing to around 1.8 meters (6 feet), the kitefin’s luminescence makes it the largest luminous vertebrate known to science. The blackbelly and southern lanternsharks were similarly luminescent but they are comparably diddy sharks at just 47 and 60 centimeters (1.5 to 1.9 feet) long respectively.

luminescent sharks
As the above images show, the blackbelly lanternshark pales by comparison to the kitefin, being much smaller and not so glowy. Image credit: Jerome Mallefet et al 2021.

Exactly why the sharks have evolved to glow like this isn’t clear, but the researchers posit it could be for improving their hunting success. The luminescence could prove beneficial in illuminating the murky depths and revealing prey, or as a means of disguise when making its approach, but more research will need to be done to ascertain if either theory holds water.

“Bioluminescence has often been seen as a spectacular yet uncommon event at sea but considering the vastness of the deep sea and the occurrence of luminous organisms in this zone, it is now more and more obvious that producing light at depth must play an important role in structuring the biggest ecosystem on our planet,” wrote the study authors. “This first experimental study of three luminous shark species from New Zealand provides an insight into the diversity of shark bioluminescence and highlights the need for more research to help understand these unusual deep-sea inhabitants: the glowing sharks.”

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