Bioluminescence

Bioluminescence in water lapping shore

Bioluminescence

by Andrea Freeman

         Marvels abound in profusion throughout the natural world and ranking highly among them is the phenomenon of bioluminescence. Of the 80 orders of animals, a whopping 40 of them have at least one species that glows in the dark! These run the gamut from microscopic plankton and bacteria to Japan's poisonous Moonlight Mushroom which may grow to 6" in diameter.
	 The luminous protozoa are mainly the dinoflagellates such as Noctiluca, Ceratium, and Gonyaulax. ¬(Noctiluca scintillens is large enough (0.5 mm) to be seen with the naked eye.) They shimmer in the water with a bluish-green light when the surface is disturbed by wind, waves, fish, swimmers or boats. They abound in the oceans worldwide, but are particularly noticeable in our hemisphere in the late summer, during periods of planktonic blooms. These blooms are generally triggered by an increase in the availability of nutrients in the water, which, in turn, is often spurred by upwelling and the amount of vertical mixing going on. However, dinoflagellate blooms also occur locally in the Bay Area during relaxation periods, when downwelling is prevailing and the winds are out of the south. Salinity, density and temperature are also key factors.
	Bioluminescence is ubiquitous, but is more prevalent in some places than in others. A report released by the Naval Oceanographic Office states, "The Arabian Sea isprobably the most luminous sea in the world, and is also the source for some of the more unusual reports of surface bioluminescence."
	Bahia Fosforescente, on Puerto Rico's southwest coast, is also renowned for its bioluminescence. There, the waters shimmering with luminosity can be seen on any night of the year, and often cause a swimmer to glow as if with a greenish "fire." This light is even bright enough to read by!
	The U.S. Navy has devoted considerable attention to the study of bioluminescence for security reasons; ships passing through areas of high luminosity light up the waters as they pass, making them clearly visible from afar, even on a moonless night. Submarines can also be detected in this way.
	In the phylum Cnidaria, the luminescent creatures include hydroids such as Obelia, scyphozoan jellyfish such as Aurelia and Cyanea, and some gorgonians. Almost all the common ctenophores such as Pleurobrachia, Mnemiopsis, Benroe ovata, and Cestus are bioluminescent. Ectoprocts (bryozoans) also glow, as do numerous annelids, especially the polychaetes.
	On October 11, 1492, Christopher Columbus observed a phenomenon that looked like "moving candles in the sea." By this time, his exhausted crew was on the verge of mutiny, and he had promised them that if land was not reached within three days that they would turn back. Encouraged by this glow in the night, as perhaps heralding land ahead, they had the renewed fortitude to go on. The next day the Santa Maria landed on the island of San Salvadore!
Biologists now believe this glow to have been from the mating performance of the Bermuda annelid fireworm Odontosyllis . Their mating ritual occurs only on three or four nights after the full moon and about fifty-five minutes past sunset. The female worm rises to the surface of the sea from her coral reef habitat below, and emits a bright bluish glow while she swims round in circles. Her lights may attract one or many male fireworms, which also surface and flash their lights in response. The female's entire body shines with a steady light, the male has but two small headlights. For fifteen to thirty minutes, they light up the sea like "moving candles". The female, still swimming in circles, releases a luminous stream of eggs to which the male adds his sperm, after which the adults return to their benthic burrows.
Biologist L.R. Crawshay examined old almanacs dating back to the time of Columbus's voyage and the occasion of his sighting and determined that the phase of the moon and time of sunset coincided precisely with when the fireworm's ritual should occur. (Talk about being in the right place at the right time! The presence of these little polychaetes literally affected history, and I think they deserve to be given national recognition and status alongside our eagle or perhaps instead of it!)
	Another history-altering event caused by invertebrate intervention occurred in 1634. The English were preparing to invade Cuba when they saw myriad lights on shore. Assuming these lights to be torches held by Spanish forces already on the island, they believed themselves to be greatly out- numbered, and so sailed on rather than attacking. Historians now suspect that these "torches" were actually thousands of luminescent fire beetles! These beetles, Pyrophorus (which means fire-carrier), found on the islands of the Caribbean Sea, often grow to two inches and resemble an unusually large firefly. (The more common firefly is only about a half an inch or less.) It is a type of click beetle, called cucujos by the local people because of the clicking sound it makes. It has a flickering, heart-shaped orange light on its abdomen, visible only when the beetle is in flight, but it also has two large, round greenish-yellow lights, one on each shoulder, which are visible even when the beetle is stationary. These lights so resemble the headlights of a car that Pyrophorus is also nicknamed the "automobile bug." The natives tie them to their hands and feet to light their way through the jungle at night, and also keep them in cages to light their houses. Five of them provide enough light to read by. Women also put them in mesh bags and use them as glowing hair ornaments.
 	Another intriguing creature is Phrixothrix, a beetle found in South and Central America. It looks more like a worm than a beetle, and the larval form and the adult female light up in two colors if stimulated. The wingless adult female form may attain two inches in length. It has two red "headlights" (it is one of the few insects that produces red light) as well as eleven pairs of greenish-yellow lights running along the sides of its body. It can control how many of these lights it has lit at any given time. When its sides are totally lighted, it resembles a miniature passenger train with its windows illuminated and so is commonly called "el ferrocarril,"  the railroad worm.
	Other luminous invertebrates include sponges, echinoderms, especially the brittle stars, many mollusks, but primarily the cephalopods (octopi and squid), though some marine snails and clams also glow, and arthropods (crustacea such as copepods, shrimp, glowworms, fireflies and other beetles.) Fish are the only animals with backbones to possess bioluminescence. No amphibians, reptiles, birds, or mammals have this ability. There are bioluminescent bacteria and fungi as well.
	Bioluminescence is common in a multitude of marine organisms, but to date, only one freshwater animal is known to light up. It is a small black snail, the size of a raisin, known as Latia. It is found in brooks and rivers of New Zealand, where it clings to stones and feeds on algae. Scientists have determined that it indeed produces its own green light, rather than being a host to luminous bacteria, which was originally suspected.
	So what is bioluminescence? In centuries past, all sorts of conjectures were put forth. The glowing trunks of trees were once believed to be enchanted by magic. In Italy, it was thought that fireflies shone with the spirits of the dead. Aside from the superstitious beliefs, theories to explain lights in the sea ranged from them coming from the oily slime of fishes, to them being the result of heat absorbed by the water during the day. Benjamin Franklin once suggested that the ocean's phosphorescence was caused by friction between waves and the air. Aristotle did make an accurate observation that the lights of glowing creatures gave off no heat. Bioluminescent light is, in fact, incredibly efficient in this way. Unlike the standard electric light bulb which produces only 10% light while giving off 90% heat, firefly light is almost 100% pure light.
	The first real scientific inquiry into understanding bioluminescence was made in the late 17th century by an English chemist named Robert Boyle. By pumping air in and out of bell jars under which he had put glowing meat, fish and wood, he discovered that oxygen was required for bioluminescent organisms to light up, and that when deprived of oxygen, they would cease to glow.
	In 1885, more than two hundred years later, a Frenchman named Raphael Dubois conducted experiments in his laboratory at Tamaris-sur-Mer in France, with our favorite fire beetle, Pyrophorus. He separated and ground up its two light organs (bad day to be a fire beetle), mixing one with hot water, the other with cold water. The cold water mixture glowed for a few minutes before going out, whereas the hot water mixture did not glow at all, even after it cooled. "Ah ha! Heat must have destroyed whatever produced ze light!" he reasoned, "and what was een ze cold water must have gotten used up!" He then mixed the cold solution which had stopped glowing with the solution which had once been heated and had never glowed, and lo and behold, the combined mixture lit up! He repeated the experiment many times with the same results, and later substituted the luminous juice of the clam, Pholas dactylus, in place of the beetle's light organs. (This clam shines with blue light in five places on its body.) Again the results were the same. From these experiments he deduced that there were two substances involved in producing the light; the one unaffected by heat he named luciferin. (Lucifer in Latin means "bearer of light"). The chemical destroyed by heat he believed to be an enzyme, and named it luciferase. Luciferase denatures when the temperature rises above 50º C. (Enzymes cause chemical changes without being used up themselves, and are easily destroyed by heat, hence his deduction.) His profound discovery paved the way for further research on the subject by other scientists.
	Notable among them was a Dr. Harvey at Princeton University, and Ethel, his biologist wife, who devoted the next forty years to the study, describing and classifying all known bioluminescent organisms and writing books on the subject. Though he worked with the fireworm, fireflies, and luminescent shrimp, the study of Cypridinia hilgendorfii, a small crustacean from Japan, was of particular interest to him. It is more commonly known as the "sea firefly." (Note: I have recently seen Cypridinia referred to as Vargula hilgendorfii, but I don't know if the name change is official.) It is found in the shallow coastal waters around Japan, and is no larger than a cucumber seed. It looks like a tiny clam with a transparent shell. During the day, it remains in the sandy substrate, but at night it uses its tiny side legs to swim to the surface to feed. If disturbed, it leaves behind a trail of bright blue light, which is how it acquired its sea firefly nickname. Dr. Harvey found that the bright blue light it generates is made by luciferin and luciferase produced by separate glands in its body.
	C. hilgendorfii attained almost legendary status for the role it played during the Second World War. It was gathered by the bushel for use by Japanese soldiers out in the jungle, for when crushed and moistened in their hands, it provided them with a dim light by which to read their maps, instead of using flashlights or matches, which could have given their position away. Powdered Cypridinia, when moistened, will still shine after twenty-five years!
	Dr. Harvey also made the important discovery that every bioluminescent organism produces its own special chemicals, and that the luciferin and luciferase of one differs from and is not interchangeable with those of another. They do not fit together chemically to produce light. An organism's respective type of luciferin and luciferase determines the color of the light it will emanate, which can vary considerably. Most marine organisms produce blue and blue-white light, which travels greater distances in water than other colors do, whereas terrestrial creatures employ a broader spectrum of colors such as the red, green and yellow lights which bedeck the Phrixothrix beetle mentioned earlier.
	In 1946, Dr. William McElroy, a scientist at John Hopkins University, conducted research to investigate what causes differences in the brightness of firefly light. His experiments revealed that the amount of adenosine triphosphate (ATP) present determines the level of brightness. In the presence of ATP, luciferase acts on luciferin, releasing light as a result of metabolic oxidation. ATP provides the energy to drive the reaction.
	This discovery has had far reaching applications in medicine. With ATP removed, firefly extract becomes a means to test for the presence of ATP elsewhere. Bacterial infections can be detected by mixing luciferin and luciferase with urine samples, since a healthy person's urine would contain no bacteria and hence no ATP. When firefly extract, with the ATP removed, is placed on healthy body cells it will light up, since the cells themselves supply sufficient ATP. But when it is added to cancer cells, which by their nature have little ATP, less light is produced, thus serving as an accurate method for cancer detection.
	 It has also been determined that pH effects the length of time luciferin and luciferase will glow, the optimum pH being 7.8. Experiments with adding dilute acetic acid or sodium hydroxide have revealed that the glow will appear and disappear as the pH is altered back and forth.  
	In 1961, scientists at Johns Hopkins figured out how to synthesize firefly luciferin for use in research, but it is only very recently that a gene clone for luciferase has been achieved. (Note: The sea fireflies mentioned earlier, Cypridinia/Vargula hilgendorfii, are an exception to the rule in that they do not require ATP for their bioluminescence.)
	Some bioluminescent organisms are responsive to specific substances and will light up when in contact with them. The paddle worm, a sedentary polychaete that lives in a U-shaped tube on the ocean floor, emits a sticky blue-green slime that lights up in the presence of iron. As such, paddle worm extract was used in blood tests to successfully diagnose anemia, though it has now been replaced in this function by more sophisticated technology.
	The jellyfish Aequorea requires calcium for its bioluminescent reaction, the only organism known to have this requirement; the lights rimming its dome will glow only when in contact with this mineral. Both Aequorea and the paddle worm contain a single lighting chemical called a photoprotein, in which the luciferin and luciferase are joined together as one, with oxygen packed in alongside. Calcium frees the oxygen, permitting the light-producing reaction to take place. Extracts of Aequorea called "aequorin" are used for measuring calcium levels in the blood. Up until recently, the jellyfish's lights had to be removed to obtain the extract. Ten tons of jellyfish were needed to yield only 1/200 of an ounce (a milligram was enough for thousands of tests), but fortunately biochemists are now able to cultivate a recombinant form of this photoprotein. 
	The bioluminescent protein, as isolated from a number of species of the jellyfish Aequorea, is a single chain polypeptide. It contains bound oxygen and a heterocyclic compound called coelentrazine. The protein contains three calcium binding sites, and upon addition of calcium ions, the protein oxidizes the coelentrazine using the bound oxygen to produce a flash of blue light.
	Aequorin, covalently attached to antibodies to thyroid stimulating hormone (TSH), is currently being employed in tests for diagnosis of thyroid function. Prior to this method being adopted, thyroid tests relied on the use of radioisotopes, which can be harmful. It is also used to detect the presence of strontium, a dangerous radioactive waste product of atomic explosions, as it also causes this extract to light up.
	Bacteria are the smallest bioluminescent organisms, and can be seen individually only under a microscope. Some measure only 1/20,000 of an inch. Their light does not flicker but shines constantly even during the day, though trillions of them would be needed even to equal the output of one 60-watt bulb.
	 Some species of luminous bacteria are partial to decaying fish and animal flesh. Over the years, there have been many eerie sightings of a strange glow emanating from the dead and wounded on battlefields. During the American Civil War, doctors sometimes observed a dull light coming from their patient's wounds. This was considered to be a good sign, however, for these glowing wounds reportedly healed more rapidly than those that were not illumined. In fact, rather than being harmful, the luminous bacteria serve to remove dead tissues which could otherwise attract disease-causing microbes. Luminous bacteria can also appear on food before spoilage, and studies have proven that it is not at all harmful to eat. This bacteria can be easily cultured in salt water with nutrients added. (I can envision a whole new trend emerging in nighttime dining in Marin--bioluminescent sushi!)
	In 1900, Dubois (the French scientist mentioned earlier) created quite a sensation at the Paris International Exposition by filling large glass flasks with luminous bacteria and illuminating a whole room with their blue-green light, to such an extent that people were able to sit and read their newspapers by it.
	One strain of luminous marine bacteria has been found to glow in the presence of marijuana, heroin, cocaine, and explosives like dynamite. The freeze-dried bacteria have been incorporated into a small portable detector used by officials at airports and harbors.
	Bioluminescent genes from another marine bacterium have been used in creating a bacteria that is able to detect pollutants such as naphthalene, a constituent of diesel fuel, by lighting up when exposed to them.
	At McGill University in Montreal, bacteria has been developed that glows in the presence of aluminum, mercury and other metals. The luciferin and luciferase of Cypridinia (the crustacean previously described) become inactive and unable to light up when exposed to pollutants from jet fuels, and can also serve as a gauge of air pollution. Firefly extract, which lights up in the presence of ATP, has been used to detect harmful bacteria in drinking water. Bioluminescent organisms could in fact become the microscopic equivalent of the miner's canary.
	 Some fungi are also known to be bioluminescent. Molds and mushrooms may be found glowing with a dull yellow or green light on rotting tree trunks, branches, and piles of decaying wood. Stinkhorn fungi is one species known to be bioluminescent, as is the moonlight mushroom in Japan. The luminescence can emanate from the mycelia, the cap, or the entire organism. The glow from stinkhorn fungi is known colloquially as "fox fire," and over the centuries was considered to be of mystical and magical origin.
	In the seventeenth century, Swedish farmers were known to use wood infected with glowing fungi to illuminate their haylofts, in lieu of using a torch which could easily have set the loft ablaze. During the Second World War, an American reporter on the island of New Guinea recounted writing a letter home to his wife by the light of five mushrooms. Biologists believe that fungi use this light to attract insects, such as flies, who will inadvertently pick up the spores and disperse them elsewhere.
	Another application of bioluminescence is in the field of agriculture. Experiments are underway in using it to monitor various crop conditions. At the University of Alberta in Calgary, a bacterial gene for luminescence has been spliced into soybeans, making the roots glow a vivid blue when the plant is deficient in nitrogen. It is theorized that bioluminescence could eventually be used to make crops glow when they need water, fertilizer, or are under siege by insects, enabling farmers to be more efficient in their use of water or chemicals. Clarence Kado, a UC plant pathologist, has suggested that illuminating bigger plants might not be such a bad idea either. He proposes cultivating shrubs to light up urban highways and airport runways, or, one of his favorite ideas: a bioluminescent Christmas tree!
	 Cyanobacteria is currently being utilized in research experiments to try to understand the molecular mechanism of the oscillator responsible for circadian rhythms. A highly sensitive photon-counting camera allows for monitoring the bioluminescence of individual colonies that display the same behavior as circadian rhythms in higher eukaryotes.
	Aside from its relevance for human purposes, and perhaps more importantly, luminous bacteria also play a vital role in the mesopelagic zone of the ocean (656 to 3280 ft. beneath the surface), a region beneath the limits of effectual light penetration. Much of the particulate matter and detritus that floats suspended in these waters will glow if disturbed. The vast majority (estimates range from 96% to 99%) of the animals inhabiting this zone are capable of producing light, via light-producing organs called photophores. Photophores are connected to the nervous system of the animal and are biochemically activated. Like flashlights, they have built-in lenses to focus the light and reflectors to cast it out.
	The colors of light generated range from lilac, purple, orange, yellow and yellow-green, to blue-green and blue, the latter being, by far, the most common. (In the ocean, red fades away at a depth of 20 ft., orange at 150 ft., yellow at 300 ft., and below 800 ft. only blue prevails.) However, not all of these animals can produce light on their own. To achieve this end, a mutualistic relationship has evolved between certain marine organisms and luminous bacteria, such as the bacterium Vibrio fischeri .
	This bacterium settles into the light-emitting organs of certain marine fish and squid by the millions, where in exchange for room and board, the host is provided with the ability to emit light! V. fischeri is also found in lower densities in sea water, where it exists as bacterioplankton. In the planktonic state, light production serves it no significant purpose and would be a waste of energy. As such, some species of V. fischeri possess a genetic control mechanism  that enables light to be produced when the bacteria is in the photophores of a host, but does not allow synthesis of the light emitting system while it's in the planktonic habitat. Wow! Talk about energy efficiency! (Note: Some scientists believe the luminosity of planktonic bacteria and dinoflagellates does indeed serve a function, that of attracting small fish who will in turn draw larger fish who will likely consume the former, the bacterioplankton then partaking of the leftovers. Pretty impressive strategic planning for a bacterium, if true!)
	V. fischeri is known to colonize in the light-emitting organ of the Hawaiian squid Euprymna scolopes, the newly hatched squid becoming inoculated with the bacterial cells present in the ambient sea water. Research has revealed some curious findings in this regard.
 	It has been determined that there are actually two types of V. fischeri that inhabit Hawaiian seawater, one which is visibly luminous (VL), and one which is non-visibly luminous (NVL). Interestingly, only the NVL strains are recruited from the water to become light organ symbionts of E. scolopes even though VL strains are also present in the same environment.
	In laboratory inoculation experiments, VL strains, when presented in pure culture, showed the same capability for colonizing the light organ as NVL strains. In experiments with mixed strains, however, the VL were unable to compete with the NVL strains and did not persist within the light organ as the symbiosis became established. Additionally, NVL entered light organs that had already been colonized by VL strains and displaced them. The mechanism underlying the symbiotic competitiveness exhibited by NVL strains remains unknown.
	The bacteria-bearing light organs of various creatures are highly specialized to suit the needs of the host. Many fish use their lights to attract prey. A notable example is the anglerfish, whose lighted sac of luminescent bacteria dangles at the end of a long stalk, like a fishing line, that extends from the tip of its dorsal fin. This lighted lure bobs just in front of its fiercely-toothed, cavernous jaws which are ready to snap shut when the prey arrives. Curiously, it is only the females who have these lighted lures in all but two of the ninety species of deep-sea anglers. To compensate, the males (who are only six inches long) will attach themselves permanently to a female (who can attain a length of three feet) by biting into her flesh and drawing their nourishment from her body. In return (?!), the male provides sperm when the female is ready to lay her eggs. As many as three males may be attached to a single female at the same time!
	The flashlight fish Sparus palpebratus, a denizen of the Indian and Pacific oceans, employs its bacterial lights in numerous ways. Divers have nicknamed this fish "le petit peugeot" due to it having photophores under each eye which it can cover and uncover like pop-up lights on a car. Its special "eyelid" is cream-colored on the outside and black on the inside and completely blocks out the light when it is closed. The fish's headlights help it to see where it is going and to both spot and lure prey. It also uses its lights to defend its territory. Should another fish swim near, the flashlight fish shuts off its lights, swims up close to the intruder and then suddenly blasts on its lights to startle the fish away. When trying to elude the pursuit of a bigger fish, it blinks its lights rapidly on and off while swimming in zigzags, effectively confusing the potential predator. Males and females also use their lights to signal to each other when they're ready to mate.
	In the shallows of the Bandu Sea by Indonesia, two other fish are found with the ability to shade their bacterial lights, Photoblepharon (light eyelid) and Anomalops (irregular eye) . Both fishes have a white, oval photophore under each eye that emits a bluish-white light. Anomalops is unique in that it conceals its light by rotating the entire organ into a special pocket of black tissue, whereas Photoblepharon uses the dark eyelid technique like the flashlight fish. Native fisherman use Photoblepharon's light organ as a fishing lure, by tying it to their lines. It can shine for eight hours.
	Another function of bioluminescence is that of countershading. Some fish and squid have photophores on their undersides which they can adjust to match the level of light shining down from above, which effectively erases the shadow cast when they're viewed from below. This can be particularly beneficial for those creatures who make diurnal migrations to the surface to find food.
	The pony fish (Leiognathus) is a shallow, warm water dweller of the Indian and Pacific Oceans, whose snout resembles a pony's head. It is a host to luminous bacteria which are housed in a cone-shaped organ in its abdomen, from which emanates a bluish-white light, serving to countershade the fish. The pony fish, too, possesses a cloaking device. When it wishes to descend to a depth where its light could attract predators, it covers its photophore by stretching a tissue over it.
	Countershading is employed in a different manner by the midwater squids, Chiroteuthis and Galiteuthis. Their bodies are transparent with the exception of their eyes and ink gland. Their photophores are strategically located under these organs, and shine downward to countershade them, regardless of whether the squid is inverted or upright. Instead of ejecting a cloud of dark ink as a get-away blind, which would obviously be useless in the darkness of the depths, some species of midwater squid (and shrimp, too) shoot out luciferin and luciferase which mix in the water to form a cloud of blinding brightness. Heteroteuthis is an example of one species of squid that employs this defense strategy.  (Cypridinia, mentioned earlier, also uses its blue light to stun the eyes of predators.) Some squid, like Watasenia scintillans, use their lights to attract mates. This four inch long squid is seen along the west coast of Japan in the spring, when it surfaces at night and flashes its tiny blue-white lights in hopes of finding a mate. Fisherman, spotting the lights, often get there first and scoop them up in dip nets to be later cooked and eaten, lights included. In the daylight, the photophores appear only as dark spots around the eyes and on the tips of the two longest tentacles, as well as scattered over the body. At night, the dark layer of shielding skin is pulled back, allowing the lights to shine forth.
	The brittle star, a benthic dweller, whose long, thin arms stick up out of its burrow in order to filter-feed, also uses biolumin-escence to ward off predators. If its arms are prodded by an assailant, they'll flash to try to scare it away. That failing, one of the arms will break off, and glowing brightly will wriggle away in snake-like fashion, while the rest of the creature goes dark. The missing arm can later be regenerated. Still other echinoderms possess luminous spines which serve to alert a potential predator to the fact that they are poisonous.
	Tomopterid worms are active, agile swimmers that have many paired legs running along their tapered bodies. Some species have photophores at the end of their legs, but in 1994 a new species was discovered by James Hunt and Bruce Robison, two scientists at the Monterey Bay Aquarium's Research Institute. In place of the light organs, this new species instead has pigmented pores. It's classified as a 'spewer', for when stimulated, it squirts a bioluminescent fluid from each of its leg pores. The bright yellow luminous cloud that results can completely enshroud the worm, or leave a glowing trail while he makes his getaway. A thimbleful of this discharge contains hundreds of tiny glowing rods. Scientists are perplexed as to why the color yellow should be used, since most midwater animals can only see blue-green, and they're also intrigued by the existence of the glowing rods.
	 Lantern fish are another amazing creature of the deeps. They have two white headlights that emit beams up to a foot long, as well as having lights all over their bodies and even tiny lanterns on their tongues. Their body lights help attract prey and are also used for species and sex recognition at mating time. For example, one species has three rows of lights on its abdomen, while another has two. The location of the lights differs even between males and females of the same species, which can also aid in finding a mate in the dark. The male's lights are on top of his tail and are bright, whereas the female's are located beneath her tail and are dimmer.
	For squid, shrimp and lanternfish, as well as other schooling organisms, bioluminescence also seems to serve the function of helping to keep the school together.	
	Some other memorable creatures of this dark realm include the dogfish shark and the viperfish. The ventral side of the dogfish shark (Spinax niger) is covered with tiny photophores, which serve to spotlight and startle prey long enough for the shark to attack. The viperfish has the ability to expand its mouth as a snake does, enabling it to engulf fish and shrimp almost its own size. And what a mouth it is! It can have as many as 350 lights lining its roof, which serve to attract prey into it. Like the lantern fish, the viperfish also has large lights near its eyes, but these may shine with either a steady or a flickering beam.
     An interesting phenomenon which can occur in the midwater zone is known as "contact flashing." Much of the suspended particulate matter and most of the larger gelatinous animals who inhabit this region produce light when stimulated. One animal's motion can trigger the lighting of the nearby ambient microplankton and also prompt an adjacent animal to "fire," who in turn sets off the contact flashers in its vicinity, which then cause further flashers to ignite, and so on; the progressive glow traveling through the water is like a wave of heat lightning on a summer's night.
	A terrestrial equivalent of this phenomenon can be witnessed in the Great Smoky Mountains of Tennessee, caused by a species of firefly known as Photinus carolinus. Ordinarily, they will send out five to eight flashes in unison, stop for 15 seconds, and then do it again. Occasionally, however, they'll flash in waves that ripple down the hillside like waterfalls of light! Researchers assume this to be the result of each one responding to the flashes of its immediate neighbor, much like the contact flashers of the sea or the waves of applause that occur at a baseball stadium.
	These Smoky Mountain fireflies, which have only recently (1994) come to the attention of the scientific community, are of particular interest to scientists because they are the only synchronous flashing fireflies known to exist in this country. Most other fireflies flash randomly, each one sending its own signal and responding only to the light signal of a prospective mate. The only other fireflies known to flash in synchrony are found in southeast Asia, along the banks of tidal rivers. There, the males of the species Pteroptyx mallaccae cluster on the leaves of trees in huge numbers and blink on and off in unison, looking like lights strung on a Christmas tree. These firefly trees can be seen from a half mile away. The purpose of this grandiose congregated display is believed to be that of increased visibility, since alone a firefly's signal might well get lost in the dense foliage of the swampy jungle. This spectacle goes on year round, since fireflies mate continuously in the tropics. (In the eastern United States, they mate only in the summer, usually beginning in June.)
	Different species of fireflies use different patterns of flashing lights, like a Morse code signature. Photinus pyralis (i.e. "lightning bugs"), the most common type of firefly in the eastern United States, flashes its yellow light every six or seven seconds for a duration of half a second. Other species blink quickly twice in a row, pause and then repeat the pattern. Still others use a pattern of eleven flashes. The Smoky Mountain fireflies flash within three-hundredths of a second of each other. There is yet another species that does not flash at all, instead it shines continuously with a steady glow, but these are not found in the eastern U.S. All male fireflies, of any species, flash in order to attract the attention of females. If a female is interested, she'll flash back in response and a dialogue will ensue; a little "light" conversation before sex--"Would you like to come up and see my etchings?" etc.
	When the weather turns cool, the interval between flashes becomes longer, because chemical reactions take place more slowly. Nonetheless, a female can still recognize her own species' blinking patterns, slowed down as they are, and likewise responds more slowly herself.
	Emanating light is not always to the fireflies advantage. Wolf spiders, for instance, assume they are like the neon lights at a diner, advertising an "Eat Here!" special, and they stop and enjoy a nice meal accordingly.
	There exists a "femme fatale" amongst firefly species. Photurus pennsylvanica has learned to mimic the code of as many as seven other species. Feigning ardor, she will lure a male to join her by speaking his language, and upon his arrival, she'll devour him! Some male fireflies have gotten smart to the treachery afoot, and rather than flying straight down to an answering female, instead they'll land at a safe distance and approach her very cautiously, to make sure she is who she claims to be. (Each species has its own respective scent, and within range can be identified accordingly.) Photurus males sometimes try to outwit the outwitter, by imitating the signals of other species that the Photurus females like to eat. While airborne, he'll switch from one signal to the next, and if he sees answering flashes that match his repertoire, he'll say "Ah ha!" and fly down to persuade the dexterous female Photurus to mate with him.  Another unique feature of Photurus females is that unlike most female fireflies, who are not good flyers, Photurus is adept at it and is also very strong. It's not uncommon for her to fly up after a male and catch him in the air for a quick snack. Photurus ranges from Massachusetts to Panama.
	Hopefully harboring no ill intent, a person can also attract male fireflies with the use of a penlight. To lure a male Photinus, it is suggested to shine the light about 13 cm. from the ground for one-half second. When a male responds, wait for two seconds and repeat the flash, continuing this sequence until the male approaches. As he draws near, one should move the penlight closer to the ground, dimming it against the vegetation as a real female is wont to do, so that he believes a female is shyly awaiting him.  	
	Fireflies are found on every continent except Antarctica. In Japan, firefly-watching is a national pastime and firefly-watching festivals are even celebrated. In Tokyo, where the festivals are held, air pollution is so bad that it imperils the firefly populations. To counter this, three parks have been established to raise and release the insects.  
	The earliest recorded description of fireflies dates back to about 100 B.C. when the Chinese marveled at flies with fire in their bellies, and classified them accordingly. One hundred years later, the Roman naturalist Pliny the Elder wrote about them, believing their lights to be controlled by the spreading of their wings, which is, of course, not the case. Moreover, some European fireflies exist which are wingless throughout their life, and are referred to as glowworms. (The larval stage of a firefly is also called a glowworm.)
	Fireflies are not flies at all, but are actually beetles. Like other beetles, they have four wings; the two front ones, which are leathery, are mainly protective, their delicate hind wings being the ones used for flight. Their lights are located at the posterior end of their abdomen, and can vary in color from the common yellow to orange, depending on the species.
	A female firefly lays hundreds of eggs on the underside of a leaf, which hatch out into larvae (glowworms) in about four weeks. They eat small insects, snails, and earthworms. In spider-like fashion, their poisonous bite both kills the prey and liquefies its innards, enabling them to slurp it up. The bodies of glowworms contain poisonous chemicals called lucibufagins. Scientists believe that the glow from glowworms serves as a warning to other animals that they are inedible. Birds, mice and other animals refuse to eat them.
	When the first frost comes in the Fall, the larva crawls under a rock and goes dormant until Spring. After reemerging, it resumes both its feeding and growing and the cycle repeats. The following spring, it only feeds for a couple of months, however, before digging itself a shallow pit and constructing a roof made of strips of mud derived from soil which it personally chews for the task. While in this humble abode it pupates, later to emerge as a bona fide firefly.
	A spectacular display of bioluminescence occurs in New Zealand's Waitamo Cave. The Glowworm Grotto, as it is commonly called, is home to thousands of inch-long worms, Arachinocampa luminosa, each of which emits a bluish-white light. They are actually fly larvae, who hang suspended from the ceiling of the cave in transparent tubes and dangle sticky, mucous threads to capture other insects that happen by. Once trapped, the hapless insect is reeled up on this "fishing line" into the mouth of the captor. In the blackness of the cave, the glittering, light-bejeweled ceiling creates the illusion of being the night sky ablaze with sparkling stars. So convincing is this illusion that insects are even fooled, and fly upward in the vaulted cavern seeking an exit, where instead they become ensnared in the lines. The Glowworm Grotto has become a famous tourist attraction, and more than 200,000 visitors a year descend into the underground caverns to behold the amazing spectacle. They are cautioned to be silent, for even the slightest whisper can plunge the cave into total darkness, because the glowworms, if frightened, will turn off their lights.
	All manifestations of bioluminescence are remarkable, but one of the most extraordinary is a marine phenomenon referred to as "wheels of light."
	What follows are excerpts from some of the documented reports of this enigma, which were published in an article printed in Oceans magazine in December 1987. I've paraphrased the information except when it appears in quotation marks:
 	It was a moonless night on May 9, 1983, and Chief Officer Peter Newton was on the bridge of the M.V. Mahsuri, a refrigerated cargo ship, on route to Australia. While passing through the Gulf of Oman headed toward the Arabian Sea, he first noticed "a pale green glow on the horizon just ahead of the ship, but said nothing to the cadet standing watch with him. Moments later, parallel bands of blue-green light began to sweep silently over the water toward the ship. He felt as if he should duck. Each light band was about 10 to 15 feet wide and at least 15 feet above the water. They came rapidly, every four or five seconds." In his fifteen years as a seaman, he had often seen bioluminescence, but never anything like this, and wondered if he were going mad. But indeed, the cadet was seeing it too! 
	The cadet began to transcribe onto a writing tablet what was being observed. "The ship, by then in the midst of a chaotic light show, was totally enveloped by random light movements." At this point, Newton summoned the captain from below deck, saying to bring along all others who were down there. Subsequently, they all witnessed the event. "After the first ten minutes, the bands gave way to expanding circles of light that spread rapidly, like ripples created by stones thrown into the still waters of a pond. The wheel's diameter ranged from ten feet to more than 600 feet."
	"Each wheel would last for a couple of minutes, continually flashing. Successive flashes came less than a second apart and glowed a pale green. The centers of the wheels appeared to travel along with the ship; those on the beam seemed to remain there until they faded and were replaced by a new pattern."
	Some of the crewmen were frightened and ran for cover. "As many as four light wheels were visible at once. Sometimes their outer rings would turn into long parallel bands. At the height of the activity, light circles expanded this way and that, and systems of parallel bands traveled off, seemingly in random directions. After 15 minutes of maximum intensity, the phenomenon waned, and then all was blackness again. All told, it had lasted about a half-hour."
	Newton's account is not unusual. There have been hundreds, if not thousands, of reports of this enigma witnessed by seafarers since ancient times. "Ninety-five percent of the phosphorescent wheel reports come from waters in and around the Indian and Pacific Oceans. The most frequent reports come from the Persian Gulf, the Strait of Hormuz, the Gulf of Thailand, the South China Sea, the Strait of Malacca, and the coastal seas adjacent to Karachi, Rangoon, and Bombay." One characteristic all these areas have in common is relatively shallow water, but the phenomenon also seems to show some seasonal variation. This has led some scientists to attribute the phenomenon to temperature fluctuations. Others adamantly dispute this explanation, saying temperature couldn't possibly effect the organisms to such an extent.
	Arthur Stiffey, a microbiologist at the Naval Ocean Research and Development Activity office in Bay St. Louis, Mississippi, instead theorizes that these displays are due to huge masses of marine organisms feeding on the nutritional materials running off the land during the monsoons.
	Chief Officer Newton disagrees. He believes this can indeed account for ordinary bioluminescent displays which he experiences on almost every trip, where looking over the bow of the ship everything under the water is aglow. "But, he insists, what he saw that night was totally different. What he, and others who have reported these large scale displays, saw seemed to happen above the water." He recalls that the effects were almost parallel with his line of sight. And he clearly remembers that there was no mist in the air that night, for he had taken a star sight just before the phenomenon began. Adding more credence to his objection to the nutrition explanation is the fact that samples of seawater taken by the crew of the Mahsuri did not contain any bioluminescent organisms.
	This has prompted other conjectures that the events may be a low-level atmospheric phenomenon, involving the same electromagnetic forces that cause auroras. Indeed, some of the occurrences have shown up on the ship's radar, but not always. Furthermore, comparable displays have been reported which are not aerial, but happen on and beneath the water's surface.
	In 1908, the steamship Dover, while crossing the Gulf of Mexico, "encountered two parallel corridors of luminescence, each about a half mile wide and alternating blue and green." Another sighting occurred in 1985, as the M.V. Samaria was on a course through the equatorial eastern Pacific. It encountered "what appeared to be balls of bioluminescence rising to the sea surface and spreading out into luminous greenish-white rings as large as 500 feet in diameter." The event lasted for a period of hours, and the ship's captain described it as "intense." 
	In 1959, the S.S. Bangkok was amidst a fleet of smaller fishing vessels off the coast of Indonesia, when it reported sighting "parallel flashing bands of light about eight feet wide. This gave way to radial flashing bands that looked like spokes of a giant wheel, revolving counter-clockwise, with its center located about two miles off the starboard bow. Later, a similar wheel appeared on the port bow, revolving clockwise." 
	There are so many reports of this phenomenon occurring again and again that they cannot be dismissed by scientists. Some explanations, other than those previously mentioned, are as follows:
	German hydrographer Kurt Kalle, noticed that areas of high bioluminescence are also usually seismically active, so, in 1966, he proposed that the phenomenon was caused by submarine earthquakes. His rationale was that "seismic shock waves travel upward in an expanding cone as they rise from the sea floor to the surface and stimulate luminous organisms in their passage. The interference patterns set up by multiple reflections of shock waves on the sea floor and surface could produce a variety of rotating wheels, parallel bands, and concentric circles."
	Other scientists are not convinced by this explanation. Physicist William Corliss argues, "What combination of seismic waves could stimulate overlapping, counterrotating wheels or hundreds of spinning phosphorescent crescents? Furthermore, there are several well-attested cases where the luminous displays were seen in the air well above the sea's surface. This fact, plus the persistence of the phenomenon (about half an hour on average) and the complex nature of the displays, suggests that we look for other stimuli ... "
	Mahlon Kelley, an environmental scientist at the University of Virginia, augments this dismissal by pointing out that a shock wave is not sufficient to produce such a huge display, asserting that "to get a large amount of luminescence, you must actually produce a shear, placing stress on the organism. Otherwise, it's just a compression wave, which is too slight for the organism to sense. It's hard to imagine a submarine earthquake, or something like that producing a shear stress."
	A different conjecture proposes that the phenomenon is due to collective behavior being exhibited among the bioluminescent organisms involved, much like the synchronized flashing of the Asian and Smoky Mountain fireflies described earlier. While this could possibly explain reports of concentric rings and parallel bands of light, it seems implausible that these simple organisms could communicate rotating pinwheels, and the other elaborate geometrical patterns so often seen.	
	Still another explanation for the displays of light involves "a variety of physical factors such as large-scale convergence cells and currents, winds and waves, and local turbulence and agitation." For instance, "parallel bands of light might be produced either by the intersection of a bow wave and intersecting surface waves as a ship passes through a batch of luminescent organisms, or by the refractive effects of surface waves on deeper luminescence. The wheels and their rotations could be explained in terms of the illusion of perspective on parallel bands."
	Peter Herring is considered to be perhaps the world's foremost expert on large-scale bioluminescence, and he disputes this explanation. "Even if the very large wheels are illusory, how can one explain the numerous small wheels? Or the concentric spreading rings, which cannot be a similar product of perspective?" Having noted that almost all the reports come from large ships or "large vibratory sources," rather than small boats, he believes the vessel itself is involved in creating the phenomenon. He observes that "the frequency of light pulses reported is often in the same range as the engine revolutions of most vessels," and "that the ships are often said to be at the center of the phenomenon." He acknowledges that this does not fully account for all the displays and that there may well be other explanations. 
	And well there might be, for as it stands now, none of the proposed explanations are truly convincing. Until such time as one is found, the wheels of light will continue to be one of Nature's incredible mysteries.
	And for that matter, even "ordinary" bioluminescence, exquisite as it is in all its myriad manifestations, also qualifies as being one of the awe-inspiring wonders of this fine world! 

© 1996 Andrea Freeman

 

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