Living Light, Bioluminescence

BIOLUMINESCENCE

A PHENOMENON THAT IS MORE COMMON IN THE OCEANS THAN ON LAND

During the floating classroom cruise at night, or during the s'mores beach fiesta, the question is often asked as to what are the bluish glows that are seen in the water. This is due to a phenomenon correctly called "bioluminescence," not "phosphorescence" as some people have called it. The actual cause of the pretty sparkles SeaCampers see in San Diego waters at night is mechanical agitation of microscopic plants called dinoflagellates. These tiny plants we can't see (except for the blue sparkles) are one of the two major components of the "phytoplankton," or floating plants, that produce most of the plant materials in the oceans.

The bioluminescent reaction is similar to the glow of the fireflies or the sea pansy demonstration on the floating classroom. The plant or animal produces a chemical called "luciferin" (which means light-bearing, reminding us that there is supposed to be some character who is named after this who runs around in some real hot place) and an enzyme called "luciferase" which upon reaction produces an activated "luciferin" phase which releases light. This is only done in darkness conditions, so that we don't see the bioluminescence during the day. This process was first described by E. Newton Harvey, in 1916, and he dispelled the theories that this light in the oceans was caused by friction of the waves, the water giving off the light stored during the day, or that it was some sort of electrical phenomenon (as was believed by Benjamin Franklin, who seemed to have a fixation on electricity). At any rate, the light that is produced by any living organism is called "bioluminescence," and it is not produced by phosphorus, which upon decay sometimes causes light (as in the case of decomposition of bones at times, creating an eerie "fireball").

During World War II, the U.S. Army used ground-up powders of ostracods that bioluminesce; the soldiers in the field simply took a pinch of the powder, put a couple of drops of water on it, and this emitted a dim, bluish light. The soldiers could read the maps without a tell-tale yellow light for snipers to zero in on.

Scientists differentiate the various types of bioluminescence as to whether the light is produced throughout the entire body of the organism, in certain organs called "photophores," or excreted out of the body in a mass. The dinoflagellated plants that produce the blue sparkles in the water produce the light throughout the body of the plants, fireflies and many of the deep-living fishes contain photophores, and some fish and squid eject a luminous mass out of their bodies. These same scientists also theorize on why bioluminescence is produced, and they have forwarded the following possible reasons:

1. Incidental to metabolism--probably this is the explanation for the dinoflagellates, as it is difficult to imagine why an invisible plant such as a dinoflagellates gives off light when touched.

2. Countershading--In many of the deep-living fishes, the environmental light conditions are such that there is relatively dim light and these fishes are colored so that they are dark on top and much lighter or silvery on the bottom. The photophores, when present, are directed to give off the light toward the bottom. Studies done on these fishes indicate that the intensity of the light that is emitted by these light organs matches that of the environment, so that when a predator is looking upwards at the lighted fish that is the prey, the prey becomes blurred or less visible to the predator. Likewise, when the predator is looking downward at the prey fish, it sees the dark top of the prey, which makes the prey blend in better with the darker environment.

3. Warning--some organisms are believed to luminesce to give a warning to predators that they are distasteful or toxic.

4. Defense--this seems to be the most obvious reason for most of us, as it is likely that prey can scare off a predator, or blind a predator, or distract a predator (as in the case of the squid that ejects a luminous mass out of its body and then swims in the other direction). In most cases, this mass that is lit up is a ball of bacteria.

5. Territory-staking--this might explain the bioluminescence of certain animals that are noted for establishing and maintaining "territories."

6. Illumination--in a few species of fishes, light organs are present on the snout about where one would expect headlights, with the beam directed forward. It seems apparent that these organs allow the fish to see what is going on in front of it.

7. Species/sex recognition--many of the "lantern fishes" from the deep oceans are described as separate species using the distribution pattern of the photophores as the critical characters. In some of these fishes, males possess a light organ directly in front of the tail whereas the females of the same species do not have this organ.

8. Lure--the deep-sea angler fish, which looks like a round ball with a huge mouth, has the first element of its dorsal fin (the fin on top) modified so that it contains a "light bulb" on the end. This light organ has bacteria living in it, and the bacteria give off the light when the circulatory system of the angler fish feeds oxygen to the organ. In this manner, by controlling the circulation, the fish can "turn the light on and off" and present a blinking light moving through the eternal darkness. This undoubtedly attracts curious fish and other animals of the deep, and the angler fish then opens up its cavernous mouth and captures the prey.

The dinoflagellates, with thousands of species, often reproduce in vast numbers and are responsible for the condition we call "red tide." During a red tide, at night, the observer can "see" a fish swimming through the water. Depending on the size of the blue streak, the observer's interest may be heightened. A ship passing through the waters where there are dinoflagellates abundant may leave a wake of bluish water that is visible to sensitive light meters that may stretch for up to 10 miles long! Imagine what this means to the navies of the world.

Although bioluminescence is very common in the oceans, and most phyla (large classification categories) have bioluminescent species, the abundant and easily seen Echinoderms (sea stars, brittle stars, sea urchins, sand dollars, sea cucumbers, sea lillies) contain no luminescent members. The most frequent contact with bioluminescence in the oceans still is the blue sparkles produced by microscopic dinoflagellates; thus, the next time you are at the ocean, at night, waving your arms through the water in the absence of light and watching the pretty blue stars shine, you will know that those stars are caused by tiny, floating, unseen plants.