Scientists studying sharks off New Zealand have discovered that three deep-sea species glow in the dark – including one that is now the largest-known luminous vertebrate.
Bioluminescence – the production of visible light through a chemical reaction by living organisms – is a widespread phenomenon among marine life but this is the first time it has been documented and analysed in the kitefin shark, the blackbelly lanternshark, and the southern lanternshark.
The sharks were collected during a fish survey of the Chatham Rise off the east coast of New Zealand in January 2020.
The kitefin, which can grow to 180cm, is now the largest-known luminous vertebrate: what researchers referred to as a “giant luminous shark”.
The researchers, from the Université Catholique de Louvain in Belgium and the National Institute of Water and Atmospheric Research in New Zealand, said the findings had repercussions for our understanding of life in the deep sea; one of the least-studied ecosystems on the planet.
The sharks all live in what is known as the mesopelagic or “twilight” zone of the ocean, between 200 and 1,000 metres deep, beyond which sunlight does not penetrate. Seen from below, the sharks appear backlit against the bright surface of the water, leaving them exposed to potential predators without any place to hide.
Researchers suggest these three species’ glowing underbellies may help camouflage them from any threats that might strike from beneath.
In the case of the kitefin shark, which has few or no predators, it is possible that the slow-moving species uses its natural glow to illuminate the ocean floor while it searches for food, or to disguise itself while approaching its prey.
Further study would be needed to confirm either hypothesis, the researchers wrote in a paper published in the Frontiers in Marine Science journal, as well as to understand just how the species’ bioluminescence functioned – and possible implications for prey-predation relationships.
“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 structuring the biggest ecosystem on our planet,” the researchers wrote.
Jérôme Mallefet, lead researcher from the Marine Biology Laboratory of the Université Catholique de Louvain in Belgium, said: “The luminous pattern of the Kitefin shark was unknown and we are still very surprised by the glow on the dorsal fin. Why? For which purpose?”
The size of the territories inhabited by the sharks makes this kind of study very difficult, he said. “The two other Etmopterus sharks were also not documented, so it is the first time.”
Mallefet hopes to be back out at sea soon to continue the work, and look for more luminous species.