According to a study conducted by marine biologist Jérôme Mallefet, three specific species of sharks can glow in the dark. I know what you’re thinking, ‘sharks that glow in the dark?’, get outta here. But no, it is true my friends. And yes, they are just as beautiful as you can imagine. What are these magical creatures, why have they only been discovered now, and how exactly do they glow?
The kitefin shark (Dalatias licha) is approximately the size of your average guitar. In normal light it has a brownish-black skin, with large and slightly googly eyes. But turn the lights off, and it emits an almost translucent and ghostly blue glow. On a 2020 voyage near Chatham Rise, which is just off the coast of New Zealand, a team of international scientists discovered that not only the kitefin shark, but two other species of deep sea sharks have the same gloriously bioluminescent traits. The blackbelly lanternshark (Etmopterus lucifer) and the southern lanternshark (Etmopterus granulosus) have been added to the list, although the kitefin shark takes first place for being the largest known vertebrate to produce such a glow.
The three sharks inhabit the mesopelagic zone of the ocean, which is also known as the twilight zone, and ranges from 200 to 1000 meters in depth—so obviously not a whole lot of sunlight can flood that range, providing an illuminated glow instead. According to Mallefet, most marine organisms that produce bioluminescence contain special chemicals, including a compound called luciferin that interacts with oxygen to produce light. Jellyfish, squid and algae (which are not vertebrates) for example, also enjoy luciferin. But these three shark species do not appear to contain the same chemical properties, so their ability to emit light “remains enigmatic.”
In an interview with Mongabay, Mallefet said that “For the moment our conclusion is that, maybe sharks have a new component that is unknown, But we don’t know.” As anything in nature, everything has a purpose, which is not only beautiful but inspiring when compared to how humans have evolved enough to take advantage of their surroundings.
With humanity set on living in the stars, we have neglected much of the vastness that Earth has to offer. Mallefet continues by explaining that “Many people say the deep sea is less known than the surface of the moon. We hope by highlighting something new in the deep sea of New Zealand—glowing sharks—that maybe people will start thinking we should protect this environment before destroying it. I hope the new generation will carry that message.”
Bioluminescent sharks emit light from specialised cells on the surface of their skin known as photocytes, but exactly how they do this has long been a mystery, however, the study that Mallefet and his colleagues conducted shows some interesting data: the species control their light emissions using hormones. The luminescence is turned on by melatonin, which in humans, is there to help us effectively mediate dark signals and provide night information. Melatonin has been described by the Psychiatric Times as a “hormone of darkness” rather than the ‘hormone of sleep’ we all hear about. It has also been thought to be an endogenous synchroniser that stabilises as well as reinforces various circadian rhythms in the body—the same goes for all mammals, but sharks however are of the Chondrichthyes class.
So why do sharks, among other creatures, have the ability to light up in the first place? Well, in the deep sea, scientists estimate that around three quarters of all creatures living there are bioluminescent, which in the context of darkness, can be extremely advantageous. Need I say more? I will anyway, because it’s fascinating.
Deep sea animals use this special power to do everything from attracting prey and deterring predators to using it as a means to camouflage by hiding their silhouettes to match the light around them, in turn becoming practically invisible to those big bad scaries lurking below. This trick is called counter illumination.
In the case of sharks, known as the biggest and baddest of many, the fact that there might be something after them too for supper remains a possibility. However, because of the dense concentration of photocytes that were found on the dorsal fins of the kitefin sharks, there is speculation that it might simply happen as a way to help sharks communicate with each other.
For now, it’s important to know that these creatures and their habitats are understudied, and under threat. “A lot of people know that sharks can bite, thanks to Jaws,” says Mallefet, “but few people know that they can glow in the dark.” Now for a second, look down at your hands and skin, and imagine how truly remarkable this really is.
‘Social distancing’, the term we are all very familiar with now due to COVID-19, is still very new for us—but it’s been going on for a long time in the animal kingdom. According to a recent study in Proceedings of the Royal Academy B, researchers observed how members of different species behaved around each other in the face of disease. Interestingly, evidence shows that animals have been reducing the transmission of disease in the same way we are now through social distancing for decades. Here’s what we can learn from them.
Animals that stay in groups are usually the first ones to adopt some socially distancing measures. Because living with many other animals of the same species makes it easier to capture prey or avoid predators, social animals also face a heightened risk of infection from contagious diseases. Those who socially distance during an outbreak are those that instinctively increase their chances of producing offspring. These actions are what disease ecologists call ‘behavioural immunity’, as animals can’t make their own vaccines like we do, so instead prevent it by changing how they live.
There is a strong correlation between the animals that, like humans, need community for a healthy mental state. These types of animals are less likely to isolate themselves, if even at all. Grey wolves for example, do not separate themselves from a wolf in the pack that has been infected with sarcoptic mange, because the harm of the disease is outweighed by the long term survival benefits of remaining as a pack.
Spiny lobsters have a very different set of actions to benefit their species’ long term health, they detect and avoid infected group mates that have the Panulirus argus virus 1, which kills more than half of the juvenile lobsters it infects. Young lobsters in general are easy prey for the virus because the animals are so social and share dens, corals and rocky crevices along the ocean floor.
In the early 2000s, a study was carried out to reason why some young lobsters were left to be alone. After testing the researchers found that these lobsters were infected with the virus 1 and that they had been abandoned by their fellow lobsters. These ocean crawlers spot afflicted ones by using a sniff test, which detects chemicals in infected lobsters’ urine by smelling it through the water.
These social distancing strategies sometimes mean maintaining social ties, for protection like the wolves mentioned before, or company. Another highly social animal is the mandrill—a primate that can be found in groups of tens to 100s in tropical rainforests of equatorial Africa. These groups are made up of a mix of extended family members that frequently groom each other, which deepens their social bonds as well as improves hygiene, but these behaviours change when sickness is around.
Grooming is avoided between infected and non-infected mandrills, and infections are detected again by their keen sense of smell, however, a study led by scientist and behavioural ecologist Clemence Poirotte shows that certain close relatives continued to groom each other regardless of the risk of contamination, with the sole aim of maintaining unconditional ties with relatives to reap the long-term benefits.
Humans are in the same boat as animals, and we have a long evolutionary history of infectious diseases. In the result of this history, we have built our own forms of behavioural immunity, like the feeling of disgust we have for dirty or over populated environments.
Over the years, we have developed medications and vaccines in order to help prevent the diseases we come into contact with, but time has come to introduce us to a novel disease, COVID-19. An unpredictable virus that needs time to be observed—Dana Hawley, a biologist at the Virginia Polytechnic Institute spoke to Science Magazine about social distancing in the animal kingdom, and said “a big takeaway is that social distancing works. Anytime we see a behavior that has evolved again and again in unrelated types of animals, that’s a signal that even though social distancing is a very costly behavior, the benefits clearly outweigh the costs.”