Bioluminescence is the ability of an organism to biologically produce light. On land, only some organisms like fireflies or fungi are able to produce their own light. Underwater, however, this ability is common among marine life that lives deep below, such as fish, clams, and sharks. This ability is useful in deeper levels of the ocean, where little to no light penetrates, as it allows for marine life to find food, reproduce, and as a form of defence.
Survival of this kind is caused by a chemical reaction between two chemicals: luciferin (a compound that actually makes light) and luciferase or photoprotein. While bioluminescence can be produced chemically, some organisms produce a synthetic form of luciferin. In this case, marine life use dinoflagellates (a bioluminescent form of plankton) or absorb this ability through eating other bioluminescent species or in a symbiotic relationship.
National Geographic Society. “Bioluminescence.” National Geographic. http://nationalgeographic.org/encyclopedia/bioluminescence/. Accessed July 12, 2016.
National Oceanic and Atmospheric Administration. “What is Bioluminescence?” National Oceanic and Atmospheric Administration. http://oceanexplorer.noaa.gov/facts/bioluminescence.html. July 12, 2016.