Bioluminescence is the chemical production of light by plants and
animals. Most, but not all, luminescent organisms are found in the
sea. Learn more about bioluminescence here!
By Karen Steidinger
Have you ever considered using the glowing, or luminescent
organs of certain fishes as bait? Well, the natives of the Banda
Islands do. And did you know that during World War II the Japanese
mixed dried, ground luminescent animals with water to produce a dim
light for reading maps in darkness? These are just two interesting
tales of bioluminescence-production of light by plants and animals.
The real marvel of light under the sea lies in the plants and
animals themselves: how, where, and why the light is produced.
pictures are modified from an article in National Geographic
Magazine by Dr. Paul Zaul from July 1960. Theman in the picture had twenty bucketfuls of water
poured over his head (left) from Phosphorescent Bay in Puerto Rico,
an area known for abundant bioluminescent dinoflagellates. When
lights were extinguished, this man was literally "glowing in the
Bioluminescence in the sea was once thought to be produced by
the friction of salts in seawater or by the element phosphorus and,
thus, was called phosphorescence. Today it is realized that certain
animals have special light-producing organs called photophores and
glands that emit light by a chemical reaction involving a
light-producing substance called luciferin, an enzyme called
luciferase, salts, oxygen, water, and an energy-carrying substance.
In some animals, the photophores actually harbor bacteria that
produce the light. Other organisms capable of luminescence, in
addition to bacteria and animals in the sea, belong to Protista, a
kingdom of organisms placed by scientists between bacteria and true
land plants and animals. Certain dinoflagellates and radiolarians,
both one-celled protists, are bioluminescent.
With the exception of insects and fungi, most luminescent
organisms occur in the sea. They range from single-celled
dinoflagellates and bacteria to anglerfishes with ornate
luminescent lures. In between there are light-producing sponges,
jellyfish, ctenophores (comb jellies), sea pens, squid, copepods,
shrimp, shrimp-like animals, clams, worms, brittle starfish, and
Some luminescent squid, copepods, and fishes have glands that
secrete luminous substances or bacteria. When released into the
seawater, these substances produce clouds of sparks and are thought
to function in distracting predators. The parchment tube worm known
scientifically as Chaetocterus produces a luminous slime
that possibly serves to attract prey into its tube. This form of
bioluminescence is known as extracellular; however, most
bioluminescent phenomena are intracellular processes, meaning the
animals produce light from within their bodies.
Light organs can be simple or complex. Complex photophores often
involve a layer of light-producing cells, a reflector, a layer of
pigment to prevent the light passing into the body and being
wasted, a lens or lenses, and a cornea somewhat like the human eye.
In such cases, a beam of light can be focused and controlled by
nerve impulses. A blood sinus provides oxygen for the process.
Light from photophores has been known to travel up to 30-60 feet.
In other types of photophores, luminescent bacteria produce light
continuously, and in order to control light emission in a series of
flashes, the animals have developed shutters, screens, and rotating
photophores that disappear into pouches. Luminescent bacteria are
generally not carried over from generation to generation through
the host egg; instead, they must occupy the host animal after it
has hatched. The light produced is in the visual spectrum.
Dinoflagellates, jellyfish, lantern fish, and euphausids, which are
shrimp-like animals, produce a blue light, while comb jellies
produce a blue-green light. Luminescent flashes of comb jellies and
jellyfish are among the brightest so far recorded.
Light organs can be concentrated around the eyes, mouth, or
inside the body, they can hang above the head, or they can be
scattered over the whole animal. Some fishes have a linear row of
photophores down their body, which several authors say look like
the lighted cabins in a passenger ship.
Most luminescent animals produce one or two colors of light, but
one deep sea squid produces four colors-white, deep blue, sky blue,
and red, and each color is located in a different part of its body.
The color is thought to be controlled by color screens in front of
the photophores or by differences in the chemical makeup of the
It is speculated by researchers that this efficient flashing of
cold light, with little release of heat, can function as a
protective device, a lure for food, recognition signals among males
and females, or as a light for vision. In one instance, a visual
function is excluded-the majority of luminescent copepods are
blind. To illustrate the function of signals, the males of a
species of marine worm are attracted to the flashing females during
their spawning season; a flirtatious account perhaps, but this
ritual is necessary for the survival of the species.
In bacteria, luminescence is continuous. However, in certain
one-celled organisms and animals, the light is discontinuous,
appearing as flashes that require some triggering mechanism. These
flashes can be triggered by touch, motion, light, electrical shock,
or chemicals. If a sea pen is touched in one area, it can cause
that area to glow and, in turn, may cause a wave of luminescence
over the whole animal. The sea squirt with the scientific name
Pyrosoma is comprised of closely packed individual animals
forming a hollow cylinder, and light from one colony can stimulate
another colony to glow. However, both natural and artificial light
often inhibits luminescent processes by affecting the nervous
system or the light-producing cells in the animal.
The intensity and frequency of bioluminescence is greatly
reduced in seawater more than 3,000 feet deep, but with improved
equipment, flashes from animals have been recorded from depths of
11,250 feet. Bioluminescent flashes in the deep sea must be a
startling sight for those researchers and adventurers who frequent
such depths in small submarines. But for those of us who walk the
beaches or fish at night, bioluminescent dinoflagellate blooms in
surface waters still bring a gasp of marvel. The sea aglow, whether
at the surface or thousands of feet deep, is indeed an awesome