A FLU­O­RES­CENT WORLD

Scuba Diver Australasia + Ocean Planet - - Contents - By Ni­cole Hel­ga­son

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.

WHITE 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.

DAY­LIGHT

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.

FLU­ORO 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.

EXCITED CORALS

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.

GLOW­ING ANEMONES

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

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