Bioluminescence is the emission and production of light by a living organism through chemical reactions in their bodies. It serves as a form of chemiluminescence which is plainly the emission of light as the result of a chemical reaction. Bioluminescence is exhibited by a large variety of oceanic organisms including bacteria, fishes and even large squid. The light produced by these organisms is often blue-green; in the electromagnetic spectrum, this is close to the point of maximum transmission for seawater which is most discernible and detectable by many deep-sea organisms. 

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The chemical reaction to produce this blue-green light involves two molecules: luciferin and luciferase. Luciferin is a light-emitting molecule and luciferase is an enzyme. When reacted with oxygen, they produce light which can range from red, yellow, green, blue and even violet. But in the ocean, the light produced usually is blue-green. Bioluminescence is a “cold light”, meaning that less than 20% of the light generates heat or thermal radiation. 

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Bioluminescence is most commonly used as an adaptation, its use ranging from hunting prey, defending against predators, finding mates and executing other vital activities. Some marine organisms luminesce to confuse their attackers. For instance, the vampire squid demonstrates its own variation of this defensive behavior. The vampire squid lacks ink sacs similar to many deep-sea squid. Squids that live close to the surface of the ocean eject their dark ink from their ink sacs to leave their predators in the dark and serve as a distraction for them to escape. As an alternative to this, vampire squid eject sticky bioluminescent mucus as a substitute to dark ink. This can confuse, startle and delay predators which allows for the squid to make its escape. 

Another adaptation using bioluminescence is a technique called counterillumination which is a method of active camouflage. A majority of marine species use this technique to protect themselves. Sharks and many other predators hunt from below, looking above where sunlight creates shadows beneath their prey. Hatchetfish use this technique, they have light-producing organs pointing downward. They adjust the amount of light emitting from their undersides in order to match the sunlight coming from above. Through this, they adjust their bioluminescence, disguising their shadows and becoming invisible to predators. Additionally, brittle stars, which is another bioluminescent marine animal, can detach its body parts to distract its predators. By doing so, the predator follows the glowing arm of the animal while the rest of the brittle star crawls away in the dark and escapes. Other marine animals can also detach their body parts on other animals. Sea cucumbers can break off luminescent parts of their bodies onto nearby fish when threatened. Resulting in the predator following the glow on the fish while the sea cucumber escapes. 

Taking a look at offensive adaptations, anglerfish which are the most famous predator to use bioluminescence, lures its prey through using bioluminescence. They have a filament on the top of their heads which is a long, thin, fleshy growth. On the end of the filament sits the esca which is a ball the anglerfish can light up. Some curious, smaller sized fish swim in for a closer look at the light and consequently get engulfed by the jaws of the anglerfish. Loosejaw, a type of dragonfish, uses its bioluminescence to search for prey. They have adapted to emit red light instead of blue-green. Since most fish can only see blue light, this serves as an enormous advantage for loose jaws when they light up a surrounding area. They can see their prey while their prey can't see them. 

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Bioluminescence for marine animals comes with a multitude of pros and cons for preys and predators of the deep ocean. Animals use this ‘asset’ to adapt to the living conditions of the deep sea. Whether it’s escaping from danger or hunting prey, bioluminescence serves as an essential tool for many organisms in their survival in the ocean depths.

 

Works Cited 
Encyclopedia Britannica. (n.d.). Marine bioluminescence. [online] Available at: https://www.britannica.com/science/marine-bioluminescence.
‌National Geographic (2022). Bioluminescence | National Geographic Society. [online] education.nationalgeographic.org. Available at: https://education.nationalgeographic.org/resource/bioluminescence/.