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Journey to the Center of the Earth: The Magic Behind Bioluminescence


The first time I came in contact with the idea was when I saw the movie “Journey to the Center of the Earth”. I was in awe when our protagonists fall to the center of the Earth, and Hannah sees a glowing, blue bird. It wasn’t until someone introduced in my personal vocabulary the word ‘bioluminescence’ that I understood what that magical creature was.
Bioluminescence is a light, produced by a chemical reaction in a living organism. It is a type of chemiluminescence, which is simply the term for a chemical reaction where light is produced. For this reaction to occur, the species must contain luciferin, a molecule that, when it reacts with oxygen, produces light. Some organisms can even choose the intensity and color of the lights too!
Not all bioluminescent animals produce luciferin though. Some, like fireflies or some fungi, produce their own luciferin, while others, like the midshipman fish or the squid, absorb it through other organisms, either as food or in a symbiotic relationship.
But the most beautiful thing about these creatures is that bioluminescent animals don't have to have all the same color. Light travels in waves of different shapes, or wavelengths, which determine the color of the light. When the waves hit our eyes, they are translated into colors by the brain depending on the wave. But light travels differently in land and underwater, because longer wavelengths can't travel as far in the second case. Most of the bioluminescence produced in the ocean is in the form of shorter wavelengths of light, blue-green waves, which can travel through in both shallow and deep water (although, there are some exceptions, like the dragonfish), while on land we encounter more green light-waves, tending to more yellowish tones.
There are several reasons as for why this animals can create this chemical reaction to “light up their bodies”, and some of them are:
  1. Counterillumination camouflage: In many animals living in the deep sea it’s used this kind of camouflage, in which the animal matches the overhead environmental light as seen from below.
  2. Attraction: Some species of bioluminescent creatures, like the Fungus Gnat from New Zealand, use their lights to attract prey. Some others, like the Fireflies, use it to attract mates. 
  3. Defense: Some squid and small crustaceans use bioluminescent chemical mixtures as a way of distracting a potential predator, while the animal escapes to safety. Some other animals use it to expose its predator, making it more vulnerable against threats. 
  4. Warning: Aposematism is a widely used function of bioluminescence, providing a warning that the creature concerned is not as tasty as it seems... 
  5. Mimicry: Bioluminescence is used by a variety of animals to mimic other species. Many species of deep sea fish, such as the anglerfish and dragonfish make use of aggressive mimicry to attract prey. 
Have you seen some bioluminescent species? Was it a firefly? Was it a squid? Well, sadly, for now, we don’t have any record of our little bird friend to see it in real life...

Photograph by @PublicDomainPictures
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