Marine Bioluminescence Final
This topic submitted by Adam Screeden (
screedaj@muohio.edu) at 6:55 PM on 6/7/08.
Many Miami environmental science graduate students take
the Ecology Field Courses each year.
Marine Bioluminescence
For centuries, sailors noticed that every now and then, the seas they sailed appeared to glow with a dull white light in contrast with the pitch black sky. At times, the crests of the waves exploded in blue light, and the wakes that their boats threw sparkled brilliantly. The phenomenon of bioluminescence is seen in everything from fireflies to the strangest and most grotesque creatures imaginable inhabiting the harsh environment thousands of feet below the surface of the oceans. Of the wide array of organisms exhibiting this fascinating trait, the vast majority are found in marine environments. It is estimated that up to 90% of life in the deepest oceans utilizes chemical reactions within their bodies to accomplish a wide variety of feats including mating, defense, camouflage and hunting. This evolutionary novelty is one of the most spectacular displays given by any of the creatures on our planet.
The feat of creating bioluminescence is something that could only be accomplished by a process as long, mysterious, and incredible as evolution. Fueled by natural selection, the oceans have produced a variety of creatures possessing the ability to emit light produced by chemical reactions within their bodies. These chemical reactions take on several different forms. A minimum of two chemicals is required in order for the reaction to occur in the presence of oxygen. Luciferin is the name given to any molecule that is later oxidized to produce light. Luciferase is the label assigned to the molecule responsible for the catalyzation of the oxidation of the luciferin, which creates oxyluciferin, the luminescent compound responsible for the light. In an alternative system utilizing a photoprotein, which is luciferin combined with a catalyzing protein and oxygen, an ion such as Ca2+ can be added to the photoprotein in order to produce light (Haddock et al, 1997). The various molecules termed ÒluciferinÓ are widely varied and specific to each family of organisms.
The bioluminescent organisms that produce light autogenically utilize this process in organs called photophores. Photophores are made up of photocytes, which can also work alone depending upon the organism. In some cases, nerve impulses signal this specialized tissue to release luciferase. This release is made into a chamber in the light organ full of luciferin and any other compounds necessary to the bioluminescence of the particular species. Oxygen is then introduced into the chamber and the reaction occurs giving off its byproduct, typically carbon dioxide. In some of these organisms, the ones that are always luminescent the luciferase is moved into the reaction chamber by osmosis. These organs are often equipped with filters, which allow the organism to alter the wavelength and ultimately the color of the light that is emitted before it leaves the endoderm. The vast majority of the light has a wavelength of approximately 500 nm, which appears in the blue-green spectrum as it is the one that travels the farthest in water, but some deep sea marine life give off red colors with wavelengths down to 250 nm (Haddock et al, 1997).
Few creatures can match the impressiveness with which bioluminescent dinoflagellates emit this light. These unicellular phytoplankton are responsible for the glowing boat wakes, and flashing wave crests that are occasionally seen in tropical and subtropical marine environments. These creatures use their bioluminescence to glow when disturbed. The idea being that when hunted by fish, they glow to attract even larger fish to prey upon their predators and increase their own chances of survival. A perfect example of the saying Òthe enemy of your enemy is your friend.Ó Dinoflagellates have a profound impact on the marine ecosystem. They are a primary consumer and therefore serve as food for many species of fish. On the other hand, the same creatures are responsible for the phenomena known as the Òred tide.Ó This harmful algae bloom commonly exterminates most if not all of the marine life that it comes into contact with by releasing large amounts of toxins into the water.
Bacteria, the most abundant organisms on the planet, have bioluminescent representatives inhabiting marine ecosystems. These organisms use bacterial luciferin, which is reduced riboflavin phosphate. The luciferin is then oxidized in conjunction with luciferase, oxygen, and a long-chain aldehyde according to the first process of bioluminescence production. A major type of bacteria that exhibits this trait is Vibrio harveyi which are thought to be the organism responsible for the phenomenon of the milky sea (Haddock et al, 1997). Conditions in which the bacteria reach concentrations of 108 individuals per ml of sea water produce enough light to make the sea look just slightly lighter than the night sky, giving the impression that the sea is milky in color. These bacterial blooms have been known to cover areas as large as 6,000 square miles (Haddock et al, 1997). Although the phenomenon of the milky sea has been observed by mariners for centuries, little is known about these occurrences on a large scale. Extensive information is available on the small-scale effect of the gram-negative bacterium as it releases both haemolysin and protease toxins, making the bacteria quite pathogenic and deadly to fish.
Another prominent bioluminescent bacterium is Vibrio fischeri, of the same genus as V. harveyi, but functions completely differently. V. fischeri is most commonly found in symbiotic relationships with various marine vertebrates and invertebrates. The bacteria are essentially cultured by the organisms in the light organs which contain proteins called Òreflectins.Ó These reflectins allow the animal to regulate and direct the light to serve a host of purposes. It is most widely known for its relationship to various species of squid. The bobtail squid is the most common organism that participates in a symbiotic relationship with V. fischeri. This cephalopod houses the bacteria in its light organ, located in the mantle. The organ is supplied with sugar and amino acids to feed the bacteria. The light intensity cycles due to the bacteriaÕs circadian rhythm, but is also regulated through a series of mechanisms contained in the squidÕs light organ (Dunlap, 2008). The bacteria produce more light at night, allowing the squid to make it appear lighter and thus appear invisible to anything below it as it blends in with the moonlit sky. The squid possesses a set of filters and lenses to allow it to diffuse the light produced by the bacteria to more closely mimic the light coming from the moon and stars. Bioluminescence is quite common among squid and cuttlefish, however not all of them produce light bacteriogenically.
Autogenically bioluminescent organisms are significantly more common than those who ÒproduceÓ light through their bacterial symbiosis. The benthic zone of the worldÕs oceans is one of the least hospitable places on the planet. No sunlight, low dissolved oxygen levels, and few nutrients have led to the evolution of highly adapted and extremely bizarre creatures (Rees et al, 1998). It is estimated that up to 90% of all deep-sea creatures display some kind of bioluminescent property. Fish in this environment often display characteristics far more bizarre than just bioluminescence. The cookie cutter shark has a cigar shaped body; luminescent underside, large green eyes, and eats by biting much larger animals and twisting to take a highly symmetrical piece of flesh from the animal (Hastings, 2002). Lantern fish are even stranger looking. These fish are estimated to be responsible for up to 90% of the deep sea biomass is made up of lanternfishes, bristlemouths, and lightfishes. With all but one of the 246 species of lanternfish displaying bioluminescence, the combination of lanternfish and the genera Cyclothone, commonly known as bristlemouths are estimated to be the most abundant of all vertebrate genera (Hastings, 2002). The biomass of bioluminescent organisms in the aphotic zone of the worldÕs oceans is so massive that it is estimated to be several times larger than the world fisheries catch. 550-600 million metric tons is the estimated biomass of the lanternfish, the vast majority of which possess bioluminescent capabilities meaning the glowing creatures of the sea have a much more profound impact on earth than they are typically given credit for.
These organisms receive very little attention due to the fact that they inhabit areas of our planet until recently beyond our reach. Their environments are extreme, and the adaptations the creatures have developed show that. Their bioluminescence brings light to a world that otherwise never sees it. Lights in the deep serve several primary purposes. Animals use their lights for defense, attracting prey, and mating. When these organisms moved into the harsh environments they today inhabit, they became able to create their own light, and they have found very interesting uses for their unique ability.
The Vampire Squid, one of the rarest creatures on earth and a relict as it is the only extant member of its order is a prime example of how animals use bioluminescent capabilities to evade would-be predators. The squid is completely covered in photophores, which it uses to confuse predators by flashing different parts of its body in order to confuse and disorient the attacker. In addition, it is also able to utilize photophores at the ends of its tentacles to give the illusion that it is moving farther away by drawing its tentacles together. If all else fails, the squid completes its arsenal with the ability to expel a large amount of luminescent mucus into the water before it jets off into the blackness behind the glowing cloud (Martin, 1992). Many other organisms use their bioluminescence when they migrate towards the surface. As the light shines down on top of them when they are in shallower water, they appear to any potential prey underneath them as a menacing black silhouette. This appearance can be altered by bioluminescing and matching the shade of the water, allowing the animal to almost completely disappear. This method is very popular among species that complete vertical migrations by following their prey to shallower water at night. The Hawaiian Bobtail Squid uses its relationship with V. fischeri to accomplish this task (Hastings, 2002). The Cookie Cutter Shark uses this same method, but takes advantage of a black spot on its underbelly. This spot makes the fish look significantly smaller than it actually is thereby attracting larger predators. When the predator attacks, this parasitic shark counters and bites a piece of flesh out of its prey (Martin, 1992).
The Cookie Cutter Shark is not the only developer of an ingenuous use for bioluminescence while hunting. The Anglerfish is one of the most well known of these animals. With a long, thin feeler protruding from its head and large, ferocious teeth this fish is quite intimidating. Yet, its prey never even knows that it is there. The feeler on its head is tipped with a bioluminescent organ that can be moved around right in front of the fishÕs mouth as a lure (Martin, 1992). When some unsuspecting small fish comes along to investigate the small glowing feeler, it is positioned perfectly for the anglerfish to make the fish an easy meal.
The final major function of bioluminescence is its role in the mating process. In the depths of the ocean, bioluminescence is often the only way for these creatures of the deep to find each other. During their respective mating seasons, nearly all bioluminescent organisms increase their displays either in intensity, frequency, or both. Firefly squid move to the surface during their mating season and use their photophores to emit large amounts of white light, much more than they usually do at depth the rest of the year (Martin, 1992). Some fish have different light patterns and colors depending on the sex of the individual, such as lanternfish. While relatively little is known about the mating patterns of most bioluminescent organisms as much of their activity takes place well beyond our reach, scientists are continually learning more.
All of these organisms and their abilities to glow play an extremely important role in their respective ecosystems and in the environment overall. Their unique abilities have also proven to be helpful to humans as well. V. harveyi has been discovered to be very useful in the detection of mutagens in marine sediments and soil. In addition to mutagens, scientists have also discovered how to use luciferin systems to detect bacterial contamination and there is extensive research in the medical field to utilize these unique chemical reactions to detect various diseases and disorders. Bioluminescence is also being recruited in the effort to detect landmines by announcing the presence of NO2, the primary compound released through the decomposition of TNT (Martin, 1992). In contrast to all of these noble causes, scientists have also introduced bioluminescent genes into organisms that were never meant to glow, thereby creating a wide variety of glowing creatures found in home aquariums across the world. Korean scientists have even gone so far as to create fluorescent cats, which is not quite as advanced as bioluminescence, but the animals still glow under UV light (Associated Foreign Press, 2007). It is a step in what could possibly be the wrong direction for genetic engineering.
Although the estimate places approximately 9 out of 10 deep sea species in the bioluminescent category, remarkably little is known about these organisms. For the majority of the glowing marine species, their habitat lies well beyond the reaches of conventional underwater exploration and reaching those means a lot of time, coordination, effort, and even more money. These strange and wondrous creatures are the embodiment of what centuries and even decades ago would have been figments of our wildest imaginations. Their unique ability to harness luciferin chemical reactions to provide themselves with light is a marvel of evolution that has more profound impacts on the environment and on our lives than we will probably ever know.Works Cited
Associated Foreign Press. (Dec 13, 2007). Scientists Clone Glow-in-the-Dark Cats. Retrieved, from http://dsc.discovery.com/news/2007/12/13/fluorescent-cats-clone.html
Dunlap, J. C. (2008). Salad Days in the Rhythms Trade. Genetics, 178(1), 1-13.
Haddock, S.H.D.; McDougall, C.M.; Case, J.F. (1997) The Bioluminescence Web Page. http://lifesci.ucsb.edu/~biolum/
Hastings, Woodland J. Bioluminescence. AccessScience@McGraw-Hill, http://www.accessscience.com.proxy.lib.muohio.edu, DOI 10.1036/1097-8542.083200
Martin, R. 1992. Cold Fire in the Sea. DIVER Magazine, June 1992: 18-19.
Rees, J., De Wergifosse, B., Noiset, O., Dubuisson, M., Janssens, B., & Thompson, E. M. (1998). The origins of marine bioluminescence: Turning oxygen defense mechanisms into deep-sea... Journal of Experimental Biology, 201(8), 1211-1221.
Schrope. (2007). Marine biology: Lights in the deep. Nature, 450(7169), 472-474.
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