Bioluminescence is a chemical reaction that is used deliberately for a number of reasons, whether its hunting, escaping from hunters, communication or otherwise. This can also be found in a whole range of organisms; bacteria, fungi, jellyfish and so on. But this is for another post entirely.

Biofluorescence however, is not chemical. In this case, the organism absorbs light and re-emits it as a different colour. This means the light doesn't originate from their own power source, but from an external source of light. Basically, if the organism gets hit by a high energy wave of light - typically blue or ultraviolet - this excites the molecules on the surface which then, in their ecstasy, lose some of their light energy, emitting a lower energy to our eyes - typically green or red, which are of course lower energy states of light. Think of it like dumping a surplus.

How come we never saw a glowing turtle before?

_{the protein lives within this, the hydrozoan}

Well, we did. The animals themselves aren't new to science. The Hawksbill sea turtle, or E. imbricata, and the loggerhead turtle, Caretta caretta appear to have been known at least since the 90's but possibly hundreds of years, I can't get a good date anywhere. But biofluorescence itself has only recently been discovered, for the most part since around 2004 onwards (it's not even a word according to google's spellcheck). Anything prior to that was only really seen in a particular group of proteins co-localized in a little creature called a hydrozoan.

So it's kinda amazing that its taken until now to actually notice that the turtles actually glow. But it's not as simple as just putting one in a dark light and shining a torch at it.

The deeper you go in water, the bluer things get. that's because the bandwidth of light from the sun that can penetrate all that water narrows to the higher energy blue light. This gives animals who reside or hunt at deeper depths a unique opportunity to exploit other colours. Biofluorescence, which makes use of high energy light in dark places, is rather convenient in that regard.

Ok ok, get to the turtle.

On an auspicious, full moon-lit night, 20 metres below the ocean surface on July 31st 2015, David F Gruber and John S. Sparks headed to both the coral reefs of the wild for the hawksbill turtles, and the Mystic Aquarium (seriously) in the Solomon Islands where loggerheads were being kept against their will but for their own good.

The divers built specific set-ups for the turtles with built-in blue LEDs that emitted the specific band of blue that would occur in nature and a green-ish filter of around 514 nm. With great luck they got some good shots of the wild hawksbills. This is what they saw,:

Here we have the hawksbill. As you can see, the turtle emits both green and red light in different locations. Next up was the captive loggerheads:

Surprisingly to me, the loggerheads only emitted green. The researchers supposed that the red light of the hawksbill was in fact an algal biofluorescence. But short of that, only questions remained. Why do they fluoresce at all?

They noted that the turtles had a diet that consisted of a fluorescent coral, but to date there is no evidence to suggest the two are related, and this doesn't provide a why anyway. With some creatures, there have been behavioural patterns noted, but more needs to be done regarding these delightful tetrapods.

If you want to read the paper in full You can check it out here

So there you have it. Maybe we all shine bright in the right circumstances =)

Thanks for reading!

Images from creative commons or acquired with permission