What type of animals are bioluminescent? Why?
Bioluminescence is found mainly in the oceans. Many marine organisms such as bacteria, algae, jellyfish, fish, and sharks exhibit bioluminescence. Most deep-sea animals also produce some bioluminescent light, but bioluminescence isn't only found in the deep sea, one of the most common sightings of bioluminescence occurs at the surface of the ocean. At the surface of the sea, there are many small plankton-like organisms called dinoflagellates which are bioluminescent. When conditions are right, dinoflagellates bloom in layers at the surface of the sea, causing the ocean to take on a reddish-brown color in daylight and a blue sparkly color at night. One reason why bioluminescence is found mainly in marine environments is because in the ocean, bioluminescence can help an animal survive, more so that in a non-marine environment. The most common functions of bioluminescence in the ocean are for defense against predators or to find or attract prey (food). In the deeper parts of the ocean, where sunlight is very dim or absent, more than 90% of the animals produce bioluminescent light. In addition, fresh water bioluminescence is also very rare. Fresh water habitats have not been stable for as long as the oceans, so it is more difficult for an organism to evolve something over time.
Non-marine bioluminescence is less common but many species of invertebrates such as fireflies, glowworms and spiders exhibit bioluminescence.