The Ocean Can Make Its Own Light — and Most of That Light Is Blue
Deep underwater, sunlight fades away. Plenty of animals solve the problem by carrying their own chemistry-powered lighting system.
Bioluminescence is light produced by a living organism through chemistry.
This is not an animal reflecting a torch or glowing because somebody shone ultraviolet light on it. In bioluminescence, a chemical reaction inside the organism — or in material it releases — produces visible light.
On land, fireflies are the famous example. In the ocean, the phenomenon is far more widespread, especially in the dark water column where sunlight cannot do the lighting for you.
Blue light is especially useful underwater.
Water does not transmit every colour equally. Blue light travels through seawater better than many other visible wavelengths, so a lot of marine bioluminescence sits in the blue part of the spectrum.
That means evolution has produced a world in which many animals are both making blue light and seeing blue light — an underwater visual language built around what travels best through the environment.
Light can be a lure, a warning, a disguise or a message.
Scientists do not know the function of every glowing species. That uncertainty is part of what makes the subject so good: the ocean is full of lights whose messages we have not completely decoded.
Some organisms use light in hunting, prey attraction or defensive displays.
Others use it for communication or to reduce their silhouette against faint light from above.
The words are often mixed together, but the mechanisms are different. A fluorescent organism needs incoming light to absorb and re-emit. A bioluminescent organism can generate visible light through its own chemical reaction.
The deep ocean is dark, not visually empty.
Once sunlight disappears, animals do not simply give up on light. Many of them bring their own.
Evergreen ocean-science explainer based on NOAA sources.
Where this came from.
- NOAA Ocean Exploration ↗ Overview of marine bioluminescence
- NOAA Ocean Service ↗ How bioluminescence works and what animals use it for
