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Last week I told you about the rare and beautiful blue fireflies that can be found in our state in secret remote locations. The unusual fireflies that emit a blue light rather than the typical yellow-green that we commonly see live in very specific ecological communities, some of which are found in the Smoky Mountains. If you are interested in seeing them, you can enter a lottery and hope to be chosen to go on a ranger-led nighttime hike to the hidden location.

I also told the story of how I happened to be making my first SCUBA night dive. It was there, deep in the still, quiet blackness of the Caribbean that I discovered aquatic bioluminescence. Bio means living, and luminescence means emitting light. Therefore, bioluminescence refers to organisms that have the capability of emitting light from their bodies. Fireflies are a well-known type of organism that emits light, but there are many others.

I was thrilled to be able to observe first-hand one of the other more well-known forms of bioluminescence during my nighttime dive.

As I described in last week’s column, I had joined a small group of other divers on a night dive well off the coast of a Caribbean island. The water appeared to be completely black as I entered it, but as soon as I switched on my dive light, the crystal-clear visibility allowed me to see the brilliant colors of the underwater environment.

During the day, any diver knows that most things under the surface of the ocean tend to take on a bluish appearance and colors are muted compared to those on land. This is simply the result of the diffraction of light as it passes through the depth of the water. The deeper one descends, the less light there is to illuminate objects and undersea animals and the bluer they appear.

As I discovered during my maiden night dive, however, the actual colors that exist under the surface of the sea are stunningly brilliant. Because the light is now coming from a strong white beam of a dive light rather than being filtered through 60 feet of sea water, there is no longer a bluish hue. Everything exhibits its true color. Corals, underwater animals, even fish are vibrantly colored.

Because I was used to the aqua hue of the normal vista of underwater scenes, the brightness of the colors took me by surprise. The actual living things appeared to be almost artificially colored compared to daytime views.

After a few minutes of our group being allowed to get our bearings hovering while neutrally buoyant near the ocean floor, the dive master gave us the pre-arranged signal that we would soon turn our dive lights off. We gathered into a group surrounding him and switched our lights off. At first our eyes strained to make out anything, but soon we realized that there was enough light from the abundant stars to penetrate sufficiently for us to be able to faintly see one another.

After a few minutes, the dive master swished his hand rapidly back and forth in front of him. As he did, the water began to glow. We all mimicked his actions, swishing our hands back and forth. In the wake of our hands the water began to emit a faint glow that became brighter as we moved our hands more rapidly.

We were observing the phenomenon cause by bioluminescent plankton. These tiny, often single-celled organisms are known to flash a bright light for an instant when disturbed. Because the plankton are abundant in warm waters the water disturbance caused by our hands excited the plankton sufficiently to create the visible light show. It was mesmerizing to be able to seemingly create light out of darkness in the water with just a sweep of our hands.

In fact, there are countless ocean creatures that emit light in one form or another. If you have visited remote areas of the coast at night time you may have witnessed a glow coming from the surf at times. This glow is from the bioluminescent plankton.

Some aquatic creatures emit light as a warning or distraction to predators or prey while others use the glow to attract mates. You may have seen video of the amazing angler fish, which lives in very deep, lightless water and has an anatomical variant of a dorsal spine that dangles above their head which can emit a glow to attract prey. (Only the female of the species has this structure.)

Some types of squid can actually secrete bioluminescent ink. There are countless other examples of bioluminescence that exist in the undersea world.

The phenomenon of bioluminescence is not limited to flying or swimming creatures. Next week I’ll share the story of a mysterious glowing organism that appeared during the darkest evenings during the civil war that may have saved the lives of countless soldiers. The mystery of the curious glow has only recently been solved by a couple of high school students.

Dr. Mark Kestner is a chiropractor in Murfreesboro. His office is at 1435 NW Broad St. Contact him at mkestner@DrKestner.com

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