We all know that looking at things in a different way may give you new and potentially interesting aspects of them. One of the most fascinating different way to look at things underwater is certainly fluorescence.
Fluorescence is a phenomenon by which light is absorbed at one wavelength and re-emitted at another, longer wavelength.
Most divers have already seen fluorescent, probably without knowing it. In fact, if you see an intense orange or green-yellowish coral at 20 m depth, it is fluorescing. The wavelength of these colours have been removed from the sunlight entering the water surface by the filtering effect of the water itself. Effectively, if you go diving at 20 m without any torchlight most of the colours are disappeared and everything will be bluish. So, the only way to be orange or green underwater is to fluoresce.
Fluorescent is caused by a relatively recent discovered group of proteins called Green Fluorescent Proteins or GFP. Such proteins are well conserved in the phylogeny of most of the organisms from bacteria to humans. GFP have been documented firstly in 1927 and it is one of the most important discovery of the 20th century. Indeed, it brought to the Nobel prize in Chemistry in 2008 awarded jointly to Osamu Shimomura, Martin Chalfie and Roger Y. Tsien for their studies and developments of the GFP.
To explore fluorescence, you need to dive at night. In addition to the usual equipment for a night dive (torchlight) you will need a blue LED excitation light and a yellow filter for your mask in order to better isolate the re-emitted glowing light from the organisms illuminated by the blue light.
The same equipment will be used for underwater fluorescence photography (or videography). The usual strobe may be covered by a blue filter for flashing the blue light over the organisms and freeze it for the picture. While, the camera lens will need a yellow external filter to trim the output light from the organism.
Algae strongly glow in the dark and so organisms bearing it in their tissue such as some species of corals and other cnidarians. Generally, invertebrates use to glow only in few part of the body, usually because of symbiotic relationship with fluorescent bacteria or other microorganisms. Among the echinoderms, fluorescence is not so common but some crinoids may entirely glow. Fluorescence occurs in most of the underwater species of mollusks and arthropoda, entirely or just part of their body. For example, some species of isopods, small crustaceans, may carry (or better farm!) on their back fluorescent unicellular algae (cyanobacteria) with toxins to protect themselves from predators. Among vertebrates both fish and sharks may entirely glow resembling a beautiful underwater lantern.
Fluorescence has been discovered in a wide range of organisms. However, nobody has deeply studied and quantified the number of species able to glow and, most of all, the reason why. So, we have barely scratched the knowledge and much more need to be discovered. Nowadays, fluorescence is used by scientists in a wide range of techniques: to track how cancer cells spread, how HIV infections progress and track pollutant in the environment. Fluoresce may offer a way for new insight into human health and environmental protection.
For further information:
Article of National Geographic:
news.nationalgeographic.com/2018/06/glowing-biofluorescent-oceans-animals/
Video of TED Talks:
watch the video
