A FLUORESCENT WORLD
The creatures of the ocean have a special ability that science has yet to solve: biofluorescence. Step into the fluoro world, where corals and fish glow brightly in the dark night
There is nothing quite as exciting as a fluorescent night dive. The ocean truly comes to life after dark, and it’s not just corals that glow: Some eels, sharks, stingrays, fish, and turtles also have fluorescent pigments. But being a coral communicator, my favourite organism to observe is always corals, and there is some pretty interesting science behind the glow.
HOW DO CORALS FLUORESCE?
Corals get their colours in two ways. They have photosynthetic marine algae living inside their cells which convert sunlight into energy. The brownish green colour you see in corals under normal daylight is from these algae, called zooxanthellae. When corals are bleached, they turn white because they expel the zooxanthellae.
But then there are the blues, greens, purples, and reds which come from a family of Nobel prize-winning fluorescent proteins. In short, there are protein pigments in the tissue of corals that absorb light of one colour, and re-emit light of a different colour. These pigments look different under white light, daylight, and blue light.
Using only a white light, brighter reds, orange and yellow can be seen. Some of the light is absorbed into the protein while the colour we see is what is being reflected or re-emitted. That is also why companies sell red filters to go in front of the camera to bring the red back to life.
In regular sunlight, the deeper you dive, the bluer corals will appear. Any deeper than a few metres and longer wavelengths of light such as red, orange, and yellow are quickly absorbed in the water column. Once you reach 10 metres, everything looks blue. A flashlight or external LED or strobe light will bring these colours back.
BLUE AND ULTRAVIOLET LIGHT
To see fluorescent colour, a short wavelength of light must be used, such as blue or ultraviolet (UV) light. When shone on certain corals, the protein biofluoresces, glowing a bright neon colour. The emitted fluorescence is still comparatively weak compared to the blue light, so in order to observe the phenomenon, we need to use a so-called barrier filter to block out the blue light.
Though UV lights were often used in the early days of fluoro diving, they have been found to be less effective at making corals fluoresce and may even be harmful to the organisms. We’ve been told that staring into the sun isn’t good for our eyes due to the UV light it emits. The same concept applies to marine animals. As such, today UV light has been replaced by precision blue LEDs emitting light in the range from 450 to 470 nanometres.
To see the psychedelic colours of fluorescent light, it is highly recommended to use a blue excitation light, which are commonly called fluoro lights, or fluoro torches. It’s important to purchase a blue light made with blue LEDs for fluoro diving, and not a purple hue UV light or a white light with a blue filter.
Fluoro torches feature a dichroic, interference or excitation filter in front of the lens. The filter is there to optimise the range of fluoro light and only lets a certain wavelengths pass through, while reflecting all other colours. Any new LED light that markets itself as a fluoro light should have these features.
When using a blue fluoro light, corals will glow in psychedelic shades of blue, pink, and purple. If the thought of night diving makes you feel uncomfortable, you can still see these colours during the day, although not as bright. I personally love using blue fluoro light to search for little zoanthids in the sand. They look like colourful flowers, each around three millimetres wide. The tiny polyps close when disturbed and unfurl when at rest. A fluoro light is perfect for spotting these little treasures as they light up amongst the muck.
Corals are great photography subjects, especially for fluoro diving. They hardly move around besides some swaying of the polyps so it really gives you time to dial in your settings and capture the colourful patterns.Some of my favourite corals are the Euphyllia corals. The large-polyp coral has long tentacles with tiny anchor-shaped polyps on the end. They typically glow green, but there are rare colonies that glow with a red stripe down the centre of the polyp. It’s always an interesting treasure hunt when on the lookout for these.
Another truly beautiful coral to spot with a fluoro light is the large-polyp Trachyphyllia coral. These slow-growing species are found in muck habitats. They have a small skeleton which can grow approximately five millimetres a year and it sits directly on the sand.
Above the skeleton, large vesicles and tissue are sometimes inflated with water. This helps ensure the coral doesn’t sink back into the sand.
Trachyphyllia corals are some of the most colourful corals in the world with myriad colour combinations and fluorescing patterns.
Whenever I think of fluoro diving, one picture comes to mind: a glowing tube anemone with long, fiery tentacles. During the day, the tentacles are nearly translucent but at night, under blue light, they glow in bright orange, green, and red.
Nothing is more iconic than a fluoro tube anemone. If you want to try your hand at photographing them, it is important to approach them slowly. Fast movement may cause the anemones to close up and retract into their tube.
WHERE TO GO
The beauty of fluorescent diving is that you can do it anywhere in the world. There are some dive centres that offer courses or night dives which include the fluoro torch and yellow barrier filter, but if this is something you are interested in, you can easily purchase your own equipment.
While it is ideal to dive at night and see the full fluorescent light show, a daytime dive would also allow you to observe the same psychedelic effect. Fluoro diving is a once-in-a-lifetime experience that will inspire you to see the reef with new eyes. Corals will pop off the reef in magnificent colours you’ve never seen before; anemones and fish will glow, and if you’re lucky, you might even see a bright moray eel.
OPPOSITE PAGE LEFT TO RIGHT A tube anemone under blue fluoro light during the day; a tube anemone under fluoro light and imaged through a yellow filter ABOVE Coral photographed fluorescing under blue light, seen with a yellow acrylic barrier filter
ABOVEGalaxea coral showing brilliant yellow and green fluorescence
BELOWEuphyllia corals with red stripes fluorescing under blue light, seen with a yellow acrylic barrier filter
ABOVE Tube anemones are spectacular to see on a fluorescent night dive. Their long tentacles, which are often translucent during the day, light up with a fiery display at night
RIGHT This anemone has a brilliant striped colour pattern which is only visible using a fluoro light
ABOVE Even moray eels can fluoresce