At one point or another, we all entertain the question: “If you could have one super power, what would it be?” That might always remain a hypothetical question for us humans; not that we do not have great attributes, but we always wonder what if? For example, what if you could have the ability to light up? As in have a part of your body that can emit light? Would that not be great, especially given the many power cuts we have to sit through nowadays.
Even though humans cannot physically light up, other creatures that we share this Earth with can! While we cannot see in the dark, and therefore rely heavily on artificial light to help us see when night falls, some creatures have eyes that are built to help them see at night, while others have the ability to create their own light.
The fascinating ability to create one’s own light is known as bioluminescence. The light emitted from light bulbs is usually generated by an electrical current that passes through the filament; the increase of heat in the filament causes it to emit light. However, in bioluminescent creatures, it is a chemical reaction that occurs within their bodies; the process neither needs nor gives off heat, and hence, the outcome is known as “cold light”.
Bioluminescent organisms live in different environments across the Earth, ranging from deep seas to land. If you have watched the movie Finding Nemo, you might very well remember the scene where Dory and Nemo’s dad encounter an anglerfish, lured by the lit-up dorsal fin that protrudes above its mouth.
The anglerfish can glow thanks to bioluminescent bacteria that inhabits its dorsal fin, allowing it to lure prey within easy reach of its humongous mouth, making for an easy lunch! However, not all bioluminescent life forms look as threatening; many of them are insects, such as centipedes, millipedes, and the better known fireflies.
How Do They Glow?
Bioluminescent organisms produce light through a chemical reaction known as chemiluminescence, which takes place between two types of substances: a luciferin and a luciferase. Luciferin is the light-producing substance, whereas luciferase is the enzyme that catalyzes the reaction; different chemicals can take on the role of these two. The luciferin is a photoprotein that needs a charged ion in order to activate the reaction that produces light, while the catalyst luciferase helps in speeding up the reaction.
The reaction usually needs other substances in order to take place, such as oxygen; the high energy molecule that is created by the reaction is what releases the energy in the form of light. Different species use variations of this process, and use their ability to light up by regulating their chemistry and brain processes accordingly.
Are There Different Kinds of Bioluminescent Light?
Yes, there are. The lights that different species emit vary greatly according to their habitat and the nature of the chemical reaction that takes place. In deep sea waters, only green and blue wavelengths of sunlight reach that depth, since they are the shorter wavelengths and therefore have more energy to penetrate the water at a longer distance. As a result, bioluminescent sea organisms usually emit light that is in the blue–green part of the visible light spectrum; they cannot process yellow, red, or violet colors.
Land organisms, on the other hand, can emit a wider variety of colors. While some organisms can flash lights on and off; others have a constant glow, like some species of fungi that grow on decaying wood, creating what is known as foxfire.
Why Do They Light Up?
Even though it is a wonderful ability to possess, but why do some organisms actually light up? There are many reasons: some use it to attract possible mates; others as a defensive mechanism that allows them to escape, or as a warning to predators that they are toxic; some actually use it to lure their prey, while some light up for reasons as yet undiscovered by researchers.
What Are They?
Let us have a look at some of these wonderful bioluminescent creatures, starting off with the wonderful firefly, which adds a certain mystical touch to wherever it is found. Male fireflies are the ones that usually flash on and off to attract mates; they have various lighting signals and patterns to communicate their type and that they are looking for a mate. While not all adult fireflies can glow, they can all glow as larvae in order to fend off predators and warn them that they are toxic.
Another bioluminescent organism that can be found growing on rotting trees is fungi. Not all fungi is bioluminescent but some are, and can emit green and blue light that is visible in the dark. Some speculations as to why this occurs is that the light attracts insects that then help distribute the spores of the fungi to other areas, allowing it to increase its colonies.
Bioluminescent plankton, on the other hand, lights up when disturbed, which causes a phenomenon known as the milky sea, creating a beautifully eerie sight. The plankton can light up due to waves made by passing ships, or disturbances caused by water-borne objects. They can sometimes be so strong that they can show up in satellite images of seas and oceans. Moreover, they have been known to interfere with marine navigation systems in some cases.
Image source.
We all know that squids can eject dark ink in order to envelop their predators in the dark, allowing them to escape. However, some deep sea squids lack this feature of having ink sacs; instead, some squids such as the vampire squid can eject bioluminescent mucus.
This cloud of bioluminescent mucus is ejected from the tips of its arms when it senses danger; this in effect startles the predator, allowing the squid to escape unscathed. The vampire squid also has photophores covering most of its body, which allows it to basically light up whenever it wants; this helps it attract its prey, and swim undetected in the deep dark sea when it is off.
Some marine animals have the amazing ability of detaching parts of their body to help them escape from their predators. Some species of brittle stars and sea cucumbers can detach body parts that are bioluminescent to trick their predators into going after the glowing limbs while they escape to a safer place. Sea cucumbers can detach a bioluminescent body part on a passing fish, which causes their predator to follow the fish instead of the sea cucumber; a great act of subterfuge. Many species of the brittle stars, on the other hand, are bioluminescent and even though they sometimes detach their arms they can re-grow them.
Some fish use their bioluminescent light in order to camouflage themselves and hide in plain sight; this is known as counter-illumination, and is used when fish are swimming near the surface. Near the surface, there is more light around, so fish swimming there tend to have a silhouette that is visible at greater depth. So, how do fish use bioluminescence to camouflage themselves near the surface? One example is that of the hatchetfish, which has a bioluminescent underside; by emitting light pointing downwards, mimicking the same light in its vicinity, its outline is no longer distinguishable from the surroundings, therefore becoming invisible to predators looking up.
While the hatchetfish uses counter-illumination to seem invisible, the cookie-cutter shark has a slightly different approach. It too can emit light from its underside to blend in with the light at the surface of the sea. However, it has a small part of its underside that does not light up, causing those looking up to see a small silhouette. Lured by the promise of an easy catch, they approach the shark, which then launches its attack. This trickery allows the cookie-cutter shark to prey on much bigger fish than itself.
Marine hatchetfish - Image source.
How wonderful it would be to acquire such a fabulously practical and beneficial trait. That is why many researchers are still studying this trait in organisms and some are even working on adapting the process of bioluminescence in order to create light that is as energy efficient as that produced by these animals and organisms. With so many advancements in energy studies and technologies, and with a desperately growing need for energy efficiency, let us all hope to be able soon to bioluminate!
References
livescience.com
animals.howstuffworks.com
docmo.hubpages.com
education.nationalgeographic.com
Cover Image by frimufilms on Freepik.