Bioluminescent organisms are present everywhere in our oceans, but are more abundant in the deepest parts, so why is bioluminescence so prevalent in the deep? There are several reasons: it creates individual light sources to hunt or mate, and can shockingly serve as camouflage and defense. 

First off, how does bioluminescence work? There are a few methods; the first way the glow is created is via a chemical reaction between a light-emitting molecule known as luciferin and oxygen, aided by an enzyme, luciferase. The result is a light-producing proton. Some organisms are capable of directly producing this reaction in their body. Another method of bioluminescence is the symbiosis of deep-sea organisms that cannot produce the luciferin reaction within themselves with bacteria that are capable. The colors produced range from a small variety of colors, like red, blue, green, or yellow. 

It’s no secret that the deep sea is dark, it rests below the level that surface light can reach. So, many organisms in the deep have adaptations to combat this lack of light, as they still need to eat and reproduce. How does bioluminescence help them do this? Organisms can utilize bioluminescence as a lure for prey. Anglerfish use this tactic; they have a bioluminescent lure. Prey see the glow but not the rest of the anglerfish and approach, assuming they have found a smaller glowing organism for them to eat, but instead are caught by the anglerfish. Other organisms utilize their bioluminescence to emit red light, which does not penetrate very deeply into the water. Because of this, some fish are red colored to remain “invisible” in the deep, but are easily spotted by organisms like deep-sea siphonophores with their red bioluminescence. Certain organisms, like lanternfish, utilize their bioluminescence to show off for mates, with their uniquely patterned light, so that their mates can pick out their species for mating. 

So, if light is used to bring attention to a creature, how can it be used to hide from other organisms or as defense?  Photophores on the bottom of deep-sea organisms create counter illumination, which, to other creatures below them, makes them simply look like a shadow of something much larger swimming above. It can also be used to startle predators, prey emit quick flashes of light that distract the predator and allow them to escape. Other creatures like bioluminescent octopus drop one of their glowing arms as a distraction. Sometimes, like in the case of the vampire squid, prey emit their bioluminescence in a cloud which coats their attacker in the glow, making them a target for other fish looking for a meal.  

Featured image:https://www.noaa.gov/media/digital-collections-photo/nur01004jpg