Bioluminescence is the creation of light by a living organism through a biochemical reaction.
In other words, some creatures are able to create their own light, just like we turn on the light in a room by pressing a switch.
The chemical reaction involves oxygen, an enzyme called Luciferase and a chemical named Luciferin.
The result is a cold light, with blue, light blue, green and sometimes purple colors.
Since light is one of the most important variables in the marine environment a variety of different organisms, from bacteria to fish, have developed the ability to produce light.
This light is used for communication, defense or hunting, where light is absent, for example during the night or in the very deep ocean.
In fact, sun light starts to decrease with depth. In tropical areas, once we reach 150-200 meters and below in depth, the dominant light in not sun light, but bioluminescence!
In the deep and dark ocean, bioluminescence is vital for a great variety of organisms.
The firefly squid, known as Watasenia scintillans, occurs in the Western Pacific Ocean at around 300 meter depth. It owes its name to the presence of tiny photophores through the entire body which may be flashed to attract small fish for a meal or a partner for a blind date. Furthermore, it produces light for counter-illumination camouflage: it matches the brightness and color of its ventral surface to the light coming from the surface, making it difficult for predators to detect it.
However, bioluminescence also occurs in very shallow water, for example the famous phenomenon known as “Sea of Stars”. In the Maldives, you can be lucky enough to see bioluminescence in action right on the surface of the sea, or walking on the wet sand of the beach at night. What is really happening is that so called Dinoflagellates, which are tiny unicellular algae, are stressed by the movement of the water or sand caused by our body. As a response they produce bioluminescence in order to scare you or the potential predator with this sudden and unexpected light.
There is not best season for spotting bioluminescence, so you will need a little bit of luck to see this natural firework in the water. In any case, it is a great bonus after your sunset snorkeling or during a night walk.
For further information, an interesting talk about bioluminescence with amazing videos:
https://www.ted.com/talks/edith_widder_the_weird_and_wonderful_world_of_bioluminescence
http://theconversation.com/what-is-bioluminescence-and-how-is-it-used-by-humans-and-in-nature-100472
For more scientific information about mechanisms, diversity, and ecology of bioluminescence in dinoflagellates:
