As you probably know already, many sea living creatures are capable of emitting their own fluorescent light. Turning yourself into a living light bulb comes in handy when you live at depths where no sunlight or only very little sun light is capable of reaching you, and the glow can for instance be used for communication, as camouflage, or to lure in prey.
Up until now, most fish experts have assumed that marine fish living below a depth of 10 metres (30 feet) could not be red since the type of sunlight necessary for the colour red to be visible to the eye isn’t capable of travelling so far down into the ocean, and why would an animal develop a red pigmentation that nobody could see in its natural habitat?
New light has now been shed on the situation and – according to a study published on September 15 by researchers at the University of Tubingen in Germany – fish living at these depths have managed to circumvent the problem of light scarcity by emitting their own red fluorescent light instead of relying on sun beams to display their colours. According to the study, a lot of marine species are capable of emitting a fluorescent red light which can be seen even at depths below 10 meters.
“The general consensus, which dominated fish literature for 20 or 30 years, was that fish don’t see red very well or at all,” says Nico Michiels, one of the researchers behind the study. “We have been blinded, literally, by the blue-green light that is available on reefs in the daytime.”
The scuba diving research team made their discovery when looking through a filter that blocked out the brighter green and blue light waves. While using the filter – which leaves only red light waves – the scientists realised that their dive spot was inhabited by a long row if different marine creatures capable of emitting their own red light. In addition to fish, they saw fluorescent red coral, algae and other small organisms.
Further investigation revealed that the red glowing organisms use guanine crystals to produce their light. Guanine is one of the five main nucleobases found in DNA and RNA and guanine crystals are commonly used by the cosmetics industry to give products such as shampoo, eye shadows and nail polish a shimmering lustre. As early as 1656, a Parisian rosary maker named François Jaquin extracted crystalline guanine forming G-quadruplexes from fish scales – so called pearl essence. Guanine crystals are rhombic platelets composed of multiple transparent layers and the pearly lustre appears when light is partially reflected and transmitted from layer to layer.
The red fluorescent light emitted by the organisms studied by Michiels and his colleagues is only visible at a close distance, at least to us humans. More research is now needed to investigate why so many sea dwellers have developed this capacity and how the red colour benefits them in their daily life.