Our group prepares to leave Lighthouse Cave, San Salvador, Bahamas.
Thousands of feet below the surface, the waters of the ocean are cold, still, and dark. Almost no sunlight can penetrate such depths, and the water temperature hovers near freezing. The harsh conditions of the abyss have generated some of the most nightmarish bizarre-looking creatures on Earth. Here there is a need for a cool light that will help organisms find their way through the dark murky waters, this light that is produced from a cool chemical reaction unlike sunlight (which is thermal) or electrical light is know as bioluminescence. Bio means living and luminescence means Ňgiving off light.Ó Luminescent organisms give off different types of light and not all organisms use their luminescence the same way. Some luminescent organisms use their light all of the time, or receive the light from bacteria growing on their bodies. Others flash their light(s) on and off whenever they choose. These lights are used to communicate, to camouflage, to guide, to attract mates, to lure prey, and sometimes to frighten enemies. The many animals and organisms that produce this glow are generally found in the deep sea or in shallow ocean waters at night, but also can be found in caves, grasslands, forests, and even in your own backyard.
In the ocean, bioluminescent organisms are everywhere, inhabiting all the depths and covering all the world's oceans. The most common organism which uses bioluminescence, dinoflagellates, can be found virtually everywhere in the sea. This phytoplankton (plant-like microscopic organisms) gathers by the thousands to create red tides. This name coming from the red-brown color that overwhelms the oceans do to their immense numbers. These organisms produce streaks of electric blue light that highlight breaking waves during the night. The red tide phytoplanktons use their flashes as a type of security alarm to avoid being eaten. Any stimulation of the cells creates flashes of light which is intended to scare away predators.
The ocean currents hold countless tiny swimming and floating organisms called dinoflagellates. These creatures appear greenish white. The largest dinoflagellates is about 1 millimeter, which is about the size of the period at the end of this sentence. At night, when they are disturbed by passing boats, fish, or heavy waves, they sparkle like jewels. Even a bubble pushing on them causes their tiny membranes to change shape and emit light. These dinoflagellates exit mostly in salt water. They are found in many shapes, some even with protective plates or shells. They get their food from dissolved scraps of leftovers from larger fish.
One well-known area to see luminescent dinoflagellates is in Puerto RicoŐs Phosphorescent Bay, on the islandŐs southwest coast. The 60 acre lagoon is attached through a narrow link to the CaribbeanŐs gentle tides and vitamin-rich water. Every night of the year this bay is said to produce an erie glow. Millions of microorganisms produce billions and billions of chemical reactions and turn the ocean waters into a giant nightlight. In this bay, even dipping your hand in the water supposedly causes it to glow like a ghost.
Most Caribbean phosphorescent bays have been destroyed by buildings on the coastland. Commercial development had changed the waterŐs quality, quantity, and nutrient supply. The most recent study available in 1987 in a U.S. Navy report, saw only 14 phosphorescent bays left in the world. No extreme measures have been focused on the preservation these dinoflagellates or the glowing bays, but currently seem to be thriving. People never seem to worry about thriving organisms, but perhaps in the years ahead there will be more attention on these little guys.
Moving downward, in the perpetual darkness of the deep sea, where sunlight never reaches bioluminescence serves other purposes. Anglerfish grow luminescent bacteria in a special structure which dangles at the end of a stalk projecting from their forehead. This stalk is a modified spine from the dorsal fin called an illicium. Just as fishermen use a glowing lure for night fishing, in the perpetual darkness of the deep sea these fish attract prey by their glowing lures. Some deep-water anglerfish can catch and eat prey as much as three times their length. Of deep-water pelagic fish, the anglerfish are the most diverse. They are sometimes smooth-skinned, sometimes spiny, generally of a velvety-black complexion.
The ocean is a very vast and open space. Keep in mind that water makes up 73% of the earth. The ocean is first divided into two separate categories, penthos and benthos. Benthos refers to the bottom of the ocean and the organisms living there. We will focus more on the open water. The uppermost layer of the penthos ocean is called the epipelagic, or eutrophic (good light) zone. It begins at the surface and ends as deep as 650 feet. Beneath this surface layer - from depths of 650 to 3300 feet - is the mesopelagic, of disphotic (bad light) zone. At the bottom of the pelagic sea is the aphotic (without light) zone, between 3300 feet and the sea floor.
The epipelagic zone is a clear well-lighted place, a region where fish like the tuna, the king fish, the sailfish, the marlin exist. Underneath, far more voluminous, is the mesopelagic zone of dimness and dark, inhabited by mid-water squid and fish of habits weird and aspects strange. This is a transition zone. It is the floor of the zone of light, the ceiling of darkness. It is inhabited by creatures with exquisitely photosensitive eyes and bodies spangles with photophores and luminescent splotches. "In mesopelagic fish, eyes are generally large to enormous, with retnas composed entirely of rods for detection of light. Photopores are often large and numerous, central nervous system fairly well developed, sense of smell moderately acute, skeleton well ossified, muscles well developed, swim bladder usually present, gills filamentous, heart and kidneys large. In fish of the deeper, dark zones, eyes are small, photophores are small, central nervous system weakly developed, skeleton weakly ossified, muscles poorly developed, swim bladder absent or regressed, gills reduced, heart and kidneys small" (Brower pp39) The number and diversity of inhabitants are greater here than in any of the layers below; until one reaches the bottom.
There are basicly three different types of luminescence found in organisms, all of which are found in species of squid. Internal luminescence is light produced within the tissues held by special cell structures called photophores. External luminescence is light produced in the water through secretions ejected from the squid. And Bacterial luminescence is light produced on the skin of the squid by colonies of luminescent bacteria living actually on the surface of the squid. While these are three different ways luminescence is exhibited, the chemical reaction is still the same.
Bioluminescent light differs from electric light and light from fire and the sun, which are warm. Bioluminescent light is a cold light. It comes from two chemical substances, luciferase and luciferin which exist inside or on the bodies of these glowing organisms. These chemicals react with oxygen and ATP to produce light. ATP (adenosine triphosphate) is a chemical energy found in all living things.
During hot summer evenings you may see flickering yellow or green lights in your back yard. These insects are known as fireflies, but they are not really flies. They are beetles with light organs under their tails.
The fireflies, or lampyrids, that you see blinking are mostly males who are searching for a mate. Each species has its own code. The male blinks his half of the code and the female, usually perched on a blade of grass, answers with the other half. There are more than 2000 species of fireflies throughout the world, each with itŐs own code. Fireflies are found on every continent except Antarctica.
The majority of humans may overlook the luminescent glow of these bioluminescent organisms, but scientists have not. More than 80% of all ocean animals show some form of luminescence and medical research has benefited greatly from these organisms by using the special chemicals of luciferase and luciferin. These chemicals have been found to help to detect disease in humans. Bacteria consist of a high amount of ATP (adenosine triphosphate). When a blood or urine sample from an ill person is combined with these chemicals, it will glow brightly if there is bacteria present, showing infection. Cancer cells and tissue damage from a heart attack can be detected by injecting these chemicals into the suspected disease area. Contamination of water, soft drinks, and wines also can be detected by adding a mixture of luciferase and luciferin. The presence of bacteria or yeast will cause the liquids to glow.
A gift from nature, these living lights are not only fascinating, but also lead to discoveries which have, and will continue to provide a better life for us all.
Brower, Kenneth. Realms of the Sea, The National Geographic Society;WashingtonD.C. 1991.
Ellis, Richard. Encyclopedia of the Sea. Random House; NewYork. 2000.
Holliday, Les. Ocean Life. Cresent Books; NewYork. 1991.
Presnall, Judith. Animals that Glow. First Books; NewYork. 1993.
Snydorman, Marty. Life in the Sea. Publications International, Ltd.; Lincolnwood, Illinois. 1994.
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