Some oceans glow at night because of a phenomenon called bioluminescence, caused by marine organisms such as plankton and jellyfish that produce light through chemical reactions in their bodies.
Marine bioluminescence is a natural phenomenon where certain organisms emit light through chemical reactions within their bodies. Most of them live in the dark depths of the ocean, where producing their own light becomes extremely useful. Often, they use this talent to attract prey, evade predators, or to attract a mate. The light produced can be blue, green, or sometimes red, but is generally blue because this color penetrates water better. This spectacular phenomenon sometimes makes the ocean at night completely magical, with glowing waves or trails when the water is stirred.
The undisputed stars of this nocturnal phenomenon are tiny but fascinating. Headlining the show is plankton. Among them, dinoflagellates shine intensely when they feel threatened or disturbed—a kind of luminous cry to disrupt their enemies. There are also small crustaceans like krill, capable of producing a bright bluish light to communicate or scare off predators. And of course, some cephalopods like squid and deep-sea fish like the famous lanternfish join these light artists to illuminate the ocean nights.
The blue-green light you see in the ocean comes from a chemical reaction in the cells of certain organisms. Specifically, it is the interaction between two molecules: a protein called luciferin and an enzyme called luciferase. When these two interact with oxygen, luciferin releases light energy: this is the phenomenon of bioluminescence. This reaction does not produce heat, hence the term "cold light." Each marine species has its own version of these molecules, which creates slightly different light hues.
Marine bioluminescence is easier to observe when environmental conditions are favorable. First, a dark night without artificial light is ideal because it greatly increases the contrast of the small lights produced by bioluminescent organisms. An absence of moon (especially during the new moon) greatly enhances observation, as even a slight moonlight can mask the luminous phenomenon. Calm water with little wave action allows the light to be clearer on the surface, while a rough sea disperses the lights and makes observation a bit more complicated. Finally, the density of bioluminescent organisms—such as glowing plankton—must be sufficiently high to produce a true light spectacle. That’s why these spectacular phenomena are often seen in nutrient-rich waters, where plankton is abundant.
Human activities influence marine bioluminescence in various ways, sometimes without us realizing it. For example, light pollution from coastal cities disrupts the natural rhythm of bioluminescent marine organisms, thus interfering with their reproductive or feeding behavior. In addition, pollutants such as agricultural chemicals or heavy metals discharged into the sea can directly affect the light-emitting capacity of certain organisms by altering their metabolism. Even the turbulence generated by boats can temporarily promote the appearance of large light shows, stimulating the reaction of glowing microbes present in the water, but in the long term, these repeated mechanical disturbances may also risk disrupting the local ecological balance essential to this fascinating natural phenomenon.
In certain specific places, such as Mosquito Bay in Puerto Rico, this luminous phenomenon is so intense that it is listed in the Guinness World Records as one of the brightest bays in the world.
Some researchers are drawing inspiration from the phenomenon of bioluminescence to develop new medical devices, for example by using light-emitting proteins extracted from marine organisms in innovative diagnostic tests.
Bioluminescent organisms are found at almost all depths of the oceans. However, in the abyssal depths where sunlight never reaches, nearly 90% of marine organisms possess this luminescent ability.
Some sailors used to rely on oceanic bioluminescence as a means of nighttime navigation. The movement of their vessel would cause the waves to shine brightly enough for them to follow a course in the dark.
Yes, human activities can indeed influence bioluminescence. Chemical pollutants, disruptions to ecosystems, and artificial light pollution alter marine habitats and can affect the distribution and proliferation of bioluminescent organisms, sometimes reducing the intensity and frequency of the observable phenomenon.
Optimal observation typically occurs during warm periods on dark nights without moonlight and minimal light pollution. The proliferation of phytoplankton, the main contributor to the phenomenon, is often encouraged by certain seasonal conditions, such as milder temperatures combined with specific maritime and climatic conditions.
To successfully photograph marine bioluminescence, use a camera with a high ISO sensitivity, a fast lens, and a long exposure on a tripod. Position yourself in a dark location without artificial lighting. Take several test shots to adjust the exposure time and increase your chances of getting a beautiful capture.
Although bioluminescence can be observed in many oceanic regions around the globe, certain places, such as some tropical or subtropical beaches, are particularly known for spectacular sightings. This mainly depends on the concentration of bioluminescent organisms present and the local environmental conditions.
No, generally marine bioluminescence is safe. It is primarily produced by tiny, non-toxic organisms, such as certain plankton or microalgae. However, it is recommended to avoid ingesting seawater and to ensure that there are no local health restrictions regarding swimming.
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