This week researchers have discovered that three deep-sea shark species have bioluminescent properties. These include the Kitefin shark (Dalatias licha), the Blackbelly Lanternshark (Etmopterus lucifer), and the Southern Lanternshark (Etmopterus granulosus) all found off the eastern coast of New Zealand. All three species produce a soft blue-green light using specialised cells in their skin called photocytes. It is thought they do this to blend into their low light surroundings to hide from predators, but also to communicate with one another.
Whilst this sounds novel, in fact over 10% of all recognised shark species can produce light. However, how these three shark species do it is a mystery. Other marine organisms which produce bioluminescence contain a mix of chemicals including luciferin which interacts with oxygen to produce light, or they have a symbiotic relationship with a bioluminescent bacterium living on their skin. These species do not appear to have the same chemical properties, nor a symbiotic bacterium, indicating a novel compound capable of light production. Furthermore, the researchers found that this novel compound was controlled by a hormone called melatonin. Melatonin typically governs diurnal cycles and induces sleep in mammals.
Humans have been fascinated by lights in the dark for centuries and harnessing the power of bioluminescence had led to huge advances in medicine. From lighting up different structures in the brain to monitoring the progression of cancer cells and tracking diseases. Additionally, bioluminescent bacteria have been used to monitor water toxicity, glowing when exposed to pollutants.
These new compounds which these three shark species may hold could be beneficial to humanity if samples are collected both sustainably and ethically. It is amazing to think that these three species of shark were just swimming around in the deep-sea, glowing and waiting for us to notice. With less known of the deep-sea than is known of the surface of the moon, we can only hope that people will consider the value of this environment before destroying it. Unfortunately, all three species are occasionally caught as unintended bycatch by fisheries, putting the populations under stress. Whilst none are considered vulnerable to extinction, little is known about their population, lifestyles, and biology so, we cannot truly be certain of their conservation status.
The deep-sea and its inhabitants are under-studied and under-threat. Hopefully highlighting these sharks’ unique properties will attract future researchers to study these sharks and their environment, so that we can learn how to better protect them.
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