Fluoro Diving: The Art and Science behind it (Part 1)

By Lynn Miner

What is Fluorescence Diving?

Fluo diving is diving with a blue light torch and mask barrier filter for viewing bio-fluorescence.  This is the property of some marine life to “emit” light with a longer wavelength (of visible light) when illuminated with shorter wavelength blue light.  This is NOT reflected light such as when you take your white light torch on a dive.  That “white light” is reflected off the reef and bounces back to your eyes/camera.  Emission light, is light the organism is creating and “emitting” back to you.  Not all marine creatures exhibit this effect but in those that do, it can be very dramatic.  Some example species that fluoresce are: many species of shelled animals, soft and hard coral structures, coral polyps, some fishes, and anemones.  Fluo diving is no longer just for night diving.  This series will discuss how it can be done with dramatic results in the daytime under certain conditions.

 What is the physics that are at play?

The visible spectrum of light is the thin slice of the electromagnetic spectrum visible to the eye.  It lies between the low energy, low frequency, extremely long wavelength radio waves and the high energy, high frequency, extremely short wavelength X-Rays.  The “bandwidth” of light wavelengths the average person can see covers from approximately 400 nanometers (nm) which is deep purple to about 750 nm dark red.

When a high energy, short wavelength photon of light (blue in our case) strikes a protein (referred to generically as a Green Fluorescent Protein - GFP), it absorbs that light energy.  This causes the electrons of its constituent atoms to make a quantum jump from one electron shell to a higher shell.  Then this change in energy state “decays” (effectively instantly) back to its resting state or shell.  When this decay occurs, the electron gives up “emits” a photon of light but at a lower energy and longer wavelength.  See figure 1.  It also emits a minuscule amount of heat, hence the lower energy state of the photon.  It’s called conservation of energy – it must all balance out.   This change in wavelength is referred to as the Stokes Shift named after the Geo. Stokes, the Irish Physicist who discovered it in the 1830’s.  We are actually talking about quantum mechanics here.  Each step, represents a quantum leap from one shell to the next.  There are no intermediate steps or jumps.  The further the jump, the greater energy required to make that jump and the greater the difference in wavelength when the electron decays.  These differences in energy show up as different colors.

fluoro diving

Figure 1

The wavelength of light used in most fluo torches is a narrow band in the blue, somewhere in the range from 440-480nm.  It has been shown that blue light is much more efficient in stimulating fluorescence of Green Fluorescent Protein (GFP) and its mutations than ultraviolet light.  This is because (as we all know from our Beginner Open Water Course), the only light available at depths beyond about 10 meters / 30 feet is blue.  This is the light organisms such as coral have evolved in over the eons and is what’s available to them for photosynthesis.  Special pigments and proteins have the ability to absorb short wavelength radiation and convert it into longer wavelengths.

It is not well understood why some corals and other sea creatures evolved to fluoresce.  What is known is that some marine organisms do produce GFP and mutations of GFP (other colors than green) which react to blue light causing this effect.

New results from scientific research show that many fishes, even deep-sea fishes, can actually see red light.  One wonders why, since there is no red light at these depths.  It has been found recently that underwater organisms actually use fluorescence to transform the only light available to them, namely blue light, into visible light of longer wavelengths, such as red (of all colors!), among others, for a number of purposes:

•  Besides from apparently protecting themselves from the harmful effects of shallow water UV radiation, as a kind of sunscreen, corals seem to do this in order to feed their symbiotic algae, which live inside their tissues.  In effect, the algae receive light from the sun on one side and light from the other side as the coral fluoresces.  This allows the corals to dwell at greater depths, where corals without this capability are unable to thrive.

•  More recent discoveries seem to suggest that perhaps fishes also use fluorescence in order not to be easily discernible from the background of fluorescing corals, which otherwise would make them easy prey, and in order to communicate between each other (within the same species), at least over short distances.

Theories as to why marine fluorescence evolved is a very active area of scientific research.  Perhaps the most obvious answer to this question is that they simply do because they are made up of elements that display the fluorescence effect.  This may seem confusing but consider this: human teeth fluoresce as do the teeth of nearly all animals.  What possible evolutionary pressure could be at work here?  The answer?  Perhaps none!  Teeth are made up of elements that fluoresce.  It may be just that simple.  Figure 2 is a perfect example.  This is Kara, my Labrador poochy. 

fluoro diving

Figure 2

 

What is the biology that makes it all work?

GFP was first described in 1955 and identified as a protein and extracted from 10,000 jellyfish in 1962.  In 2008 Osamu Shimomura, Martin Chalfie and Roger Tsien, who had worked on the subject independently, jointly won the Nobel Prize for chemistry "for the discovery and development of the green fluorescent protein, GFP". 

GFP is shown schematically below in figure 3.  The part of the protein molecule responsible for color is called the chromophore.  The chromophore is an area in the molecule where the energy difference between two different molecular electron shells falls within the range of the visible spectrum as described above.  GFP and its relative proteins have many applications in molecular biology, genetics and medicine.  This technique of using GFP as “genetic markers” is used extensively in medical research and is credited with saving 100’s of thousands of lives.

The term GFP generally refers to the first protein isolated.  Yellow, Cyan and Red fluorescent protein are simply mutations of Green GFPs.  

fluoro diving

Figure 3

 

What are applications to fluo diving other than pretty pictures?

Research at marine institutes and universities all over the world is currently underway not only to try to understand why some marine creatures display fluorescence (if in fact there is a reason) but also in the area of climate change as well as ocean temperature and acidification studies.

When water temperatures rise, coral bleaching occurs.  Corals have a symbiosis with single cell algae called zooxanthellae.  These algae use photosynthesis to provide food and energy to the coral.  Temperature rises cause these zooxanthellae to be ejected giving the coral a colorless, bleached appearance taking away the vital nutrients the coral needs to survive.  Thus, making it vulnerable to additional stresses that can ultimately destroy the entire reef.

Ocean acidification reacts with the coral’s calcium carbonate skeleton causing it to break down and dissolve.  This of course can be seen under white light conditions but it is even more dramatic using fluorescent technologies thereby enhancing this field of marine research.

This technology can be used for coral propagation census (polyp bail-out) analysis.  If you come upon a polyp or coral “recruit” release with white light, you will see little or nothing.  With the proper fluo diving gear, the individual, nearly-microscopic organisms will shine in the sand like sparkles in the snow on a moonlit night.  It is amazing to witness.  In fact, there have even been discoveries of prior unknown species because they were too small to see with white light but shine like a beacon in the dark when illuminated with blue light.

Coral reefs are considered the rain forests of the ocean and can be thought of as “the canary in a coal mine”. 

In our next instalment we will discuss the equipment used in fluo diving.

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