Scientists studying sharks in New Zealand have found that three deep-sea species glow in the dark – including one that is now the largest luminous vertebrate known.
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 that it has been documented and analyzed in the kitefin shark, in the black-bellied lantern shark and the southern lantern shark.
Sharks were collected during a fish survey at Chatham Rise on the east coast of New Zealand in January 2020.
The kitefin, which can reach 180 cm, is today the largest luminous vertebrate known: what the researchers call “giant luminous shark”.
The researchers, from the Université Catholique de Louvain in Belgium and the National Institute for Water and Atmosphere 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.
All sharks live in the so-called mesopelagic or “twilight” zone of the ocean, between 200 and 1,000 meters deep, beyond which sunlight does not penetrate. Seen from below, sharks appear illuminated behind the shiny surface of the water, leaving them exposed to potential predators with nowhere to hide.
The researchers suggest that the bright bellies of these three species may help to camouflage them from any threats that may come from below.
In the case of the kitefin shark, which has few or no predators, it is possible that the slow species uses its natural glow to illuminate the ocean floor while searching for food, or to disguise itself when approaching its prey.
Further studies would be needed to confirm any hypothesis, the researchers wrote in an article published in the journal Frontiers in Marine Science, as well as to understand how the species’ bioluminescence worked – and the possible implications for prey-predation relationships.
“Considering the vastness of the seabed and the occurrence of luminous organisms in this area, it is increasingly evident that the production of light in depth must play an important role in structuring the largest ecosystem on our planet,” wrote the researchers.
Jérôme Mallefet, chief researcher at the Laboratory of Marine Biology at the Université Catholique de Louvain, Belgium, said: “The luminous pattern of the Kitefin shark was unknown and we are still very surprised by the brightness on the dorsal fin. Why? For what purpose? “
The size of the territories inhabited by sharks makes this type of study very difficult, he said. “The other two Etmopterus sharks were also undocumented, so this is the first time.”
Mallefet hopes to be back at sea soon to continue his work and look for more luminous species.