The Living Light: How Bioluminescence Works, Why Organisms Glow, and What It Means for Our Seas

Bioluminescence

Bioluminescence means a living creature produces light. The light is not from a manufactured source such as a bulb with a battery. The light emitted is called a cold light because very little energy goes into heat; most of it goes into light. A fluorescent substance requires light to be shone upon it before it starts to glow. A bioluminescent organism is able to produce light even in complete darkness.

Where is it found?

Bioluminescence is commonly found in oceans. Because sunlight does not penetrate very far into water, organisms that live below this "sunlight zone" often produce light. In some regions, as much as three-quarters of species in the water column (the vertical section of water) could create light (data from studies). For these organisms, light is a means of camouflage, predation and communication.

1. Dinoflagellates: The glowing waves of our beaches

These are single-celled plankton too small to be seen individually. When they congregate in huge numbers, forming blooms, the sea changes. For us, Noctiluca scintillans, also called the "sea sparkle", is the most familiar of the dinoflagellates. When a wave breaks or a boat passes or a person walks through the surf, these plankton are disturbed and flash blue light for a very short time, causing the wave crest to appear to have streaks of electric blue. This was observed on our own coast at Thiruvanmiyur and Neelankarai.

2. Jellyfish and comb jellies

Jellyfish and comb jellies often have blue and green lights on them. Of the jellyfish, Aequorea victoria is of great scientific interest. A protein called green fluorescent protein (GFP) was extracted from this species. By attaching GFP to a protein of interest, the modified protein can be tracked within a cell (by its green fluorescence). This technique earned the 2008 Nobel Prize in Chemistry. Thus, a bioluminescent jellyfish has transformed research laboratories.

3. Fish

Many fish use bioluminescence for camouflage and predation. The anglerfish has a glowing lure (organism) held at the front of its head. Small fish are attracted to the lure and are eaten by the anglerfish. In several species of fish, a symbiotic relationship exists where bacteria living in the lure produce the light. Lanternfish (a type of fish) have rows of light-producing organs (photophores) along the body and are some of the most abundant fish in the oceans. Hatchetfish have photophores on the belly that serve for camouflage (see below), and other photophores on the tail that are used to lure prey.

4. Squid

The firefly squid has light organs along the body and arms that can be flashed as signals. The Hawaiian bobtail squid harbors the bioluminescent Vibrio fischeri bacteria in a special organ. The squid feeds the bacteria, and in turn the bacteria provide light, which is a textbook case of a symbiotic relationship.

5. Fungi

Some mushrooms have bioluminescent patches on them that glow green in the dark. The glow on rotting wood is called foxfire. The glow is thought to attract insects that help the mushroom by spreading its spores.

6. Others

There are also fireflies, glow-worms, millipedes, earthworms, and various luminous bacteria such as Vibrio fischeri.

Why do organisms glow?

Light has different uses for the organism, some of which are explained here.

• Defense by startle or distraction. Some squid and shrimp produce a cloud of glowing material by muscular contraction. This distracts a predator and serves the same purpose as the ink squirting of some squid species.
• Counter-illumination. Many organisms live in the mesopelagic or twilight zone of the oceans. To avoid being seen by predators looking up from below, many produce light on their ventral (lower) surfaces, thus cancelling their shadow. By emitting the same amount of light that is coming from above, they become masters of disguise.
• The "burglar alarm" effect. When under attack, some plankton (marine organisms) produce a flash of light that may attract a predator of the attacker, thus serving as an alarm call (but to another organism).
• Luring prey. The anglerfish is a well-known predator that uses a bioluminescent lure to entice prey towards its mouth.
• Finding mates. As mentioned with fireflies, the flashing is used for communication between potential mates. Some marine worms also use light flashes for this purpose.
• Communication and symbiosis. Certain organisms maintain light-producing bacteria in special organs and provide nourishment to them.

How light is produced 

The basic reaction is the same everywhere—luciferin + oxygen → oxyluciferin + light. There are variations on this theme, though, since the reaction varies from organism to organism. The luciferin within a firefly is not the same as that in a dinoflagellate or a jellyfish. This is why scientists believe that bioluminescence has evolved independently many times. Different life forms have independently discovered this incredibly useful ability. Some organisms make use of a photoprotein that holds the luciferin until certain conditions are met (e.g., presence of calcium). When disturbed, dinoflagellates send out certain messengers to trigger the reaction, and the flash of light occurs within a fraction of a second.

Why it matters to humans

• Biomedical research. Luciferase and the green fluorescent protein (GFP) are now standard research tools. They are used to determine gene expression and to follow a procedure in a living system. Luciferase can be used to track cancerous cells or the spread of infection.
• Environmental monitoring. Bioluminescent organisms can be used to detect toxins in the environment. In certain bacteria, the presence of a toxin causes the toxin to reduce the light level.
• Biotechnology. Researchers are trying to create bioluminescent plants and alternative forms of lighting. At present, the light output is very low, so this technology is still at an early stage.
• Ecology. Scientists are trying to determine how much light is present in the ocean because it is a source of illumination (in lieu of sunlight) there.

Fun facts

Glowing things in the ocean are like words in a secret language. Since sunlight does not penetrate the deep oceans, light there takes the place of visual communication. The light is used to send messages, to startle or attract enemies or prey, and to camouflage oneself from predators. Most marine organisms emit light in the blue-green spectrum, since this light travels furthest in water. Some deep-sea fish emit red light, which is invisible to other creatures and so can be used as a sort of stealth flashlight. Blooms of Noctiluca scintillans can be identified because the plankton light up when the water is agitated. If one takes a kayak ride at night while there is such a bloom, one would be able to see beautiful blue lights in one's wake.

Conclusion

Bioluminescence is one of the most beautiful ideas of nature, involving living organisms producing light for camouflage, predation, communication, and so on. From the tiny dinoflagellates that dot our own beaches to the amazing anglerfish that live deep in the oceans, bioluminescence has helped each of these organisms to thrive. Bioluminescence has provided mankind with research tools that have helped us understand nature. Bioluminescence also reminds us that the sea is a living entity and needs to be protected. So while we enjoy the view of the glowing beach, we must also remember to care for the sea and not add any more to its burden. We should also refrain from polluting the water with plastics and other materials and report any such activity to relevant authorities.