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Bioluminescence
by Amma Asare
PURPOSES | HOW | BIOLUMINESCENT ORGANISMS | LINKS
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Bioluminescence is light produced by an organism through a chemical reaction. In the ocean bioluminescence occurs at average depths of one thousand to eight thousand feet, although some exceptions occurs below this depth. Bioluminescent organisms range from bacteria and dinoflagellates to squid and fish. Two general types of bioluminescence exist. The first type, only present in fish and squid, occurs when light is produced by cultures of photophores or symbiotic luminescent bacteria that the organism maintain and manipulates through reflection or covering. The second type occurs when an organism internally produces or obtains the chemicals needed for a luminescent reaction. The light production can be extremely simple, such as a hidden flap of skin or extremely complex including a lens, reflectors and chromatophore filters. The fact that over seventy five percent of all deep sea fishes have bioluminescent capabilities raises questions about the connection between survival and bioluminescence.
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Scientists speculate that there are four natural uses for bioluminescence. The first is to escape predators. Many organisms only trigger luminescence when frightened or in danger. A sudden burst of light can blind of confuse predators, giving the organism a chance to escape. Organisms also use the technique of counterillumination by directing their glow downward at the correct angle, wavelength and intensity to make their shadows disappear. A predator hunting on the ocean floor looking for shadows of potential prey will be confused by this technique. Organisms also use their glow on specific parts of their body to blend in with sunlight filtering through the water. Another purpose for bioluminescence is to attract prey. Predatory fish use dangling lights or glowing spots inside the mouth as lures for other fish. A third natural purpose is courtship. For many species the glows identify males from females. During mating seasons organisms will glow differently than usual, showing their readiness to mate. The final purpose of bioluminescence is communication. In groups of bacteria a population density must be reached before bioluminescence will occur. Bioluminescence may be triggered by an intermolecular message between cells. Whether or not this message can be transmitted between organisms is unknown. Also the patterns of flashing light are believed to be methods of communication between organisms of the same species.
The chemical reaction responsible for the production of light bursts begins with a luciferin, a light emitter. This chemical is either acquired through the food chain or synthesized within the organism itself. Different types of organisms use different luciferins for their reactions. There are believed to be about six different types of luciferin molecules. The luciferin reacts with another chemical called the luciferase, salt and oxygen resulting in a burst of light and water. At times the necessary reactants are bound together in a single unit called the photoprotein. This molecule can be triggered to produce light by another ion, generally calcium (Ca+2).
Luciferin + Luciferase + Oxygen + Salt ----> Light + Water
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NOCTILUCA
SCINTILLANS
The dinoflagellate
noctiluca is one of the one to two percent of dinoflagellates which bioluminescence.
Noctiluca does not photosynthesize and lives by feeding off other phytoplankton
and zooplankton. Noctiluca cells are spherical with and oral pouch and one
flagellum, tooth and tentacle. They range from five hundred to six hundred
micrometers in diameter, but have been documented anywhere from two hundred
to two thousand micrometers in diameter. Their flagellum cannot propel them,
so they are considered non-mobile. The only movement possible is rotation
of vertical position by contol of the buoyancy of the cell. Not all noctiluca
are bioluminescent although most are. These dinoflagellates are responsible
for red tides. Red tides occur when a congregation of noctiluca is triggered
to luminesce at the same time due to similar vertical positions and other
mechanisms such as upwelling and currents. Not all noctiluca blooms are red,
some have been documented to be lime green.
BLACK
DRAGONFISH
A part
of the Malacosteid family, this fish has special bioluminescent capabilities.
The Black dragonfish, unlike almost all the other bilouminescent organisms
in the ocean can glow and perceive a red or blue-green light. Most other marine
organisms glow blue because that wavelength of light transmits furthest underwater
and most marine organisms lack the pigments which can absorb longer or shorter
wavelegths of light and are sensitive only to blue light. The light of the
black dragonfish can be such long wavelengths that it is nearly infrared and
barely visible to the human eye. The ability to produce this type of light
gives the black dragonfish an enourmous advantage over its prey. This fish
can shine a light to avoid predators or search for prey that does not alert
the prey or the predator to the presence of the fish since they cannot see
the light the black dragonfish shines.
The black dragonfish uses a combination of filters and fluorescent material to change the color of the light from blue to red. The intially blue light is absorbed into a fluorescent pigment which re emits it as red light, then it is filtered again until the wavelength is just enough to be invisible to other fish. Malacosteids also have an additional system to view the red light since their eyes have the same visual pigments as other fish. The red light is absorbed by a special molecule of sensitizing antenna- like pigments which captures the energy so that it can be transferred into the visual pigment that the fish have. This secondary pigment functions similarly to a neccesity to photosynthesis, chlorophyll.
Bioluminescence and Biological Fluorescence: http://www.herper.com/Bioluminescence.html