By definition, bioluminescence is the emission of light through a natural chemical reaction, and it is utilized by a variety of marine organisms.  1. Haddock, Moline, and Case, “Bioluminescence in the Sea.” It has existed for at least 400 million years and is the predominant form of communication in the ocean! In most cases bioluminescence is produced by the organisms itself and not from symbiotic bacteria, through the oxidation (the loss of an atom) of a molecule, luciferin, using a catalyzing enzyme, luciferase, or a photoprotein.  1. Haddock, Moline, and Case, “Bioluminescence in the Sea.” The biggest difference between the enzyme luciferase and photoproteins is that photoproteins do not require a catalyst, and instead emits light in combination with oxidizing agents like oxygen or hydrogen peroxide.  2. “Photoprotein | Biochemistry.”
It is important to not confuse bioluminescence with fluorescence. As stated, bioluminescence is a natural chemical reaction that is actively used by the organism to communicate. Comparatively, fluorescence is a passive trait from which photons are absorbed by a tissue and then re-emitted at a different wavelength.  3. Martini and Haddock, “Quantification of Bioluminescence from the Surface to the Deep Sea Demonstrates Its Predominance as an Ecological Trait.”
Interestingly, the use of bioluminescence seems to be used primarily in saltwater aquatic ecosystems and is near absent in lakes and rivers. Scientists speculate this discovery could be for a few reasons. First, comparatively speaking, due to its vast size, the ocean is far more evolutionarily stable than smaller aquatic systems, which are subject to more change. Second, the ocean is optically more clear than other bodies of water and thus bioluminescence is a useful tool because it can more easily be seen. Third, while the ocean is clearer than lakes and rivers, large portions of the ocean receive either no light or incredibly dim light; therefore the use of light in these areas is highly effective. Finally, there is an incredibly diverse interaction between parasites, prey and predators that are just not as present in other aquatic systems.  1. Haddock, Moline, and Case, “Bioluminescence in the Sea.”
Often bioluminescence is discussed as an exotic phenomenon, however, a study published by Martini and Haddock in 2017 demonstrates its widespread occurrence and high diversity among organisms. Over the course of 17 years video observations were recorded using a remotely operated underwater vehicle (ROV) off the coast of California. Over this observation period (which covered the surface all the way down to 3,900m) it was discovered that 75% of all recorded organisms had bioluminescent capabilities!  3. Martini and Haddock, “Quantification of Bioluminescence from the Surface to the Deep Sea Demonstrates Its Predominance as an Ecological Trait.”
Bioluminescence is used for various reasons including communication, mating, feeding, and protection. Bioluminescence can be used as a distraction to evade and confuse prey; some organisms such as Octopoteuthis deletron can detach bioluminescing limbs to lure predators in a misleading direction. Some species use it to communicate during mating to differentiate between males and females. Bioluminescence is also used as part of a protection strategy known as counterillumination where organisms light up the underside of their bodies to match the dim light coming from the surface to protect themselves from predators hunting from below.  4. “Bioluminescence | Smithsonian Ocean.”
Historically bioluminescence has been hard to study. First, the use of bright lights to study them can cause certain animals to move away. Second, bright lights can also damage light sensitive organs in bioluminescent organisms, and third, many kinds of bioluminescence cannot be seen under ordinary light.  5. US Department of Commerce, “What Is Bioluminescence?” As a result, there is still much to learn about this topic!
I hope you have enjoyed this brief overview of another incredibly interesting deep sea phenomena! If you’re interested in learning more, make sure to head over to our Youtube channel @LegaSeaTV to watch our series on bioluminescence. If you have any questions or would like to learn more about individual aspects of this topic do not hesitate to leave a comment on one of our videos or reach out directly by emailing firstname.lastname@example.org. Catch you next time!
|↑1, ↑2, ↑5||1. Haddock, Moline, and Case, “Bioluminescence in the Sea.”|
|↑3||2. “Photoprotein | Biochemistry.”|
|↑4, ↑6||3. Martini and Haddock, “Quantification of Bioluminescence from the Surface to the Deep Sea Demonstrates Its Predominance as an Ecological Trait.”|
|↑7||4. “Bioluminescence | Smithsonian Ocean.”|
|↑8||5. US Department of Commerce, “What Is Bioluminescence?”|