In order to see as many living lights as possible we are beginning our dive after dark. The light show we will witness is visible light made by living creatures also known as bioluminescence. Fireflies are bioluminescent. So are a few other land dwellers, like some earthworms, centipedes and fungi. But on land, bioluminescence is rare. By contrast, in the oceans, bioluminescence is very, very common. In fact, it would be difficult to find any place in the ocean where bioluminescence doesn’t exist.
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For a human, the deep sea is as alien as deep space. Go down several hundred feet into the ocean and the world is dark blue. Another thousand feet and your surroundings have faded to a dim bluish-gray twilight. There is enough illumination for a person to see at that depth, but too little for photosynthesis. Descend through this twilight zone another thousand feet and it is eternal night.
The darkness is not truly dark, however, and the seeming emptiness is actually full of secret messages: About 80 to 90 percent of deep-sea animals use chemicals to create bioluminescent light, piercing the gloom with signals in blue and green, orange and yellow. When it comes to understanding who is flashing whom and what it all means, though, we might as well be trying to eavesdrop on an extraterrestrial conversation.
For decades marine biologists have gotten glimpses of this glittering life by casting nets and retrieving deep-sea organisms. More recently they have lowered cameras on cables and measured the bioluminescence on display beneath the waves. Using special diving suits and submersibles, they have even entered the habitat of deep-sea organisms, watching in awe as the water world lit up with bursts of color that sparkled like fireworks. From these studies researchers have been able to glean a few basic details about bioluminescence. They know that luminescent displays signal the best mates, point the way to food, and warn of danger. The bioluminescent hatchetfish, for instance, uses its light to hide from predators by mimicking sunlight filtering through the water; the shining tubeshoulder uses bioluminescence to startle predators.
But understanding the meaning of the flashes produced by the wide swath of bioluminescent species has been impeded by one simple fact: Diving suits and submersibles frighten sea organisms, disrupting their natural behavior exactly when scientists are there to observe it. Without the ability to watch sea life undisturbed in its habitat, we have been unable to piece together the vocabulary, the grammar, or the syntax of this enigmatic language of light.
That may soon change, courtesy of Edie Widder, a cofounder of the Ocean Research & Conservation Association (ORCA) and a specialist in marine bioluminescence. She has developed a spy camera for the deep, dubbed Eye-in-the-Sea™, that is opening a window on this hidden world. The Eye sits on the ocean floor and quietly records bioluminescent organisms in their natural habitat without scaring them. Like the Search for Extraterrestrial Intelligence (SETI), Widder’s work is a bold attempt to make contact with creatures from another world. Only in this case, we know the aliens are among us.
Why does the ocean glow at night?
A nighttime cruise in the ocean can be a magical experience. Sometimes, sparkling lights in the water seem to outshine the stars in the sky.
The ocean itself doesn’t actually glow, but plenty of things that live in it do. The light they emit is called bioluminescence, and there are hundreds of different kinds of organisms on Earth that create it. Most of them live in the sea.
One kind of bioluminescence that many people are familiar with appears as sparkling streaks of light at the bow and in the wake of a moving boat in the ocean at night. The light comes from tiny, single-celled algae called dinoflagellates that live in seawater.
Water agitation prompts the light-giving chemical reaction in the dinoflagellates. Most light comes off as bluish, but different chemicals produce different colors. In the case of dinoflagellates, the intensity of light depends on the concentration of algae in the water. In some places, like the Indian Ocean, sailors have reported a soft white glow on the surface of the water — a “milky sea” that stretches as far as they can see.
Other types of bioluminescent organisms include fireflies, centipedes, fungi, squid, jellyfish, worms, and some fish.
For more information about bioluminescence visit:
- Bioluminescence web page (Univerity of California Santa Barbara)
- Harbor Branch Oceanographic Institute’s bioluminescence page
