Bioluminescence has always fascinated me. Well, glowing things in general fascinate me, but that's not my point. Bioluminescence is freaking AWESOME, okay.


First off, what is bioluminescence? It's the production of light by any living organism, basically. The word bioluminescence comes from Greek words; bios for living, lumen for light. Bioluminescence is a form of chemiluminescence, which means energy that's released in a chemical form of light. This can happen either inside or outside of the cell. Bioluminescence appears in both marine vertebrates and invertebrates, as well as micro-organisms and terrestrial animals.


Bioluminescence is a form of luminescence, and isn't to be confused with fluorescence, emission of electromagnetic radiation light by something that's absorbed radiation of a different wavelength (basically something that takes radiation, changes it to a different wavelength and shows it back) or phosphorescence, which is a type of photoluminescence that's related to fluorescence. Instead of instanly re-emitting the radiation it's absorbed, like fluorescence, it has a slower time scale. The slower time scales of the re-emission are associated with "forbidden" energy state transitions in quantum mechanics. Confusing stuff, basically. Anyway, this glowing can be re-emitted at a lower intensity for several hours at a time.


Anyway, more about bioluminescence. It's a "cold light" emission, which means less than 20% of the light generates thermal radiation. It doesn't get hot. The majority of deep-sea organisms produces bioluminescence at one point or another. Obviously, you'd have to. It's so dark, there's no light save for your own. Most marine-life bioluminescence is blue or green, like fireflies, which are the wavelengths that transmit through the water most easily. Some fish emit red and infrared light, though, and one species even emits yellow.


Non-marine bioluminescence is much less common. Obviously, the two best known non-marine bioluminescent organisms are glow worms and fireflies, however some insects, larvae, annelids (segmented worms), arachnids and even some fungi have bioluminescent properties. Some of these properties only occur at night. Some creatures give off light continually; others flash it on and off. For some, it is a warning to stay away. For others, it is a form of camouflage. Certain species of shallow water squid give off light to blend in with the moonlight. Some creatures use their light for navigation.


There are a freaking TON of bioluminescent critters, so I'll just go over some of the more common ones.


Firstly, animals. Fireflies and glowworms, as I've mentioned. Some flies, millipedes and centipedes. Quantula striata, a land snail, and annelids, which, as I've said, are segmented worms.


Fungi, which has 71 bioluminescent species, like jack-o-lantern mushrooms, ghost fungus and honey mushrooms.


Some fish are cookie-cutter sharks, anglerfish (the most commonly know, probably,) flashlight fish (fitting name, eh?), pinecone fish, and some eels.


There are a TON of invertebrae, like sea pens, coral, and jellyfish. Krill, ostracods and copepods. Mollusks and clams, sea slugs, octopi. Plenty of squids.


Micro-organisms, like dinoflagellates, which actually have a unique way of using bioluminescence. When a predator of theirs is detected, dinoflagellate luminesces, which attracts even larger predators which'll eat the would-be predator of the dinoflagellate. Vibrionaceae are also some micro-organisms.


There are several theories as to the reason of bioluminescence. One of these is attraction. Organisms use it both to lure prey, like anglerfish, or to attract a mate, like fireflies. Another use is repulsion. Some squid and crustacean species use it like octopi and squid use ink; to scare away predators. Communication is yet another use; bacteria use it at high cell densities. Lastly, illumination, obviously. Some deep-sea critters that have red bioluminescence have a red glow, which lets them see red-pigmented prey.


Bioluminescence is truly awesome, and sometimes I wish I can glow. For now, all I can do is look at pretty pictures of these lovely creatures.