Shark Scientist Lauren Smith talks to Plant Pathologist James Lynott about this incredible phenomenon.
Biofluorescence is essentially the ability of an organism, to absorb electromagnetic wavelengths from the visible light spectrum by fluorescent compounds, and the subsequent emission of this at a lower energy level.
In the marine environment, the primarily monochromatic blue spectrum that characterises large areas of the photic ocean provides a unique filtered-light environment for visual organisms. This dominant higher energy ambient blue light is reemitted at longer, lower energy wavelengths, which to the human eye results in displays of green, orange and red fluorescence.
Marine biofluorescence has been widely reported and examined extensively in cnidarians, particularly corals, however the phenomenon has only been investigated relatively recently in both cartilaginous and teleost species, where it has been found to be phylogenetically widespread and phenotypically variable (Gruber et al. 2016). Biofluorescence has even recently been observed in sea turtles (Gruber & Sparks 2015).
This revelation has led to many new questions regarding the biological and ecological role of biofluorescence in the marine realm, because both fish and turtles unlike cnidarians, possess advanced visual systems.
Recent work by Gruber et al 2016 on the swell shark (Cephaloscyllium ventriosum) and the chain catshark (Scyliorhinus retifer), both of which are known to exhibit bright green fluorescence, revealed that they both have a visual adaptation to detect the fluorescence. This coupled with the evidence that biofluorescence creates a greater luminosity contrast with the surrounding environment, and the fact that phylogenetic investigations indicate that biofluorescence has evolved at least three times in cartilaginous fishes, highlights the potential importance of the phenomenon in elasmobranch behaviour and biology.
Intrigued and keen to learn whether species that I had conducted research on here in Scotland also exhibited this phenomenon. I caught up with plant pathologist and passionate diver James Lynott, the first person to document biofluorescence in elasmobranch species found in UK waters.
What gave you the idea to start looking for biofluorescence in UK waters?
It was back in 2011 during an episode of the BBC series ‘Britain’s Secret Seas’ that I was first introduced to the phenomenon of fluorescence diving. At that time I had only been diving for a couple of years, having joined my local dive club in 2009, but was already completely hooked on British diving and the incredible diversity of marine life in our waters. It was great to see a whole TV series dedicated to British seas but it was the feature with a fluorescence night dive at St. Abbs that completely fascinated me.
I started to research the subject and found that while becoming increasingly popular in tropical areas it was difficult to find any reports or information about fluo-diving in UK waters or in fact other temperate seas.
I was keen to start trying this for myself and as I was also getting into underwater photography, I was hoping to start trying to capture it on camera too. I gradually acquired the necessary equipment (detailed below) and over the last few years I have been experimenting with fluorescence photography in UK waters which has been fascinating, the list of species that I have found to fluoresce gets bigger after nearly every dive.
What UK elasmobranch species have you captured emitting biofluorescence so far?
I have seen and captured biofluorescence in the small-spotted catshark (Scyliorhinus canicula) and thornback ray (Raja clavata). So far these are the only two species that I have been able to experiment with, but I am confident that other UK species will fluoresce.
What equipment do you use to capture this phenomenon?
To view biofluorescence I use specially developed blue lights (Light & Motion Nightsea) with a wavelength of 440-460nm, this is the excitation light that produces fluorescence in proteins and other compounds. In order to view the fluorescence effectively a yellow barrier filter is required which blocks the reflected blue light, allowing your eyes, or camera, to view just the fluorescence. I have a couple of different yellow mask filters, and for my camera a Firedivegear and Y12 yellow filter. To capture images and video I use a standard compact camera which is a Canon G7Xmk2 in a Fantasea FG7XII housing.
What colours do you typically see in UK species?
In Scyliorhinus canicula and Raja clavata so far I have just seen green fluorescence. In other fish, crustacean and anemone species I have seen green, yellow, orange, red, and purple.
Finally, what advice would you give to an underwater photographer wanting to give Bio-Fluro photography a try?
I’ve found that to be able to view fluorescence it is all about having the correct equipment. The most important thing is the lighting, a powerful light source within the correct wavelength range is essential. As fluro-diving is done in darkness and the fluorescence can be quite weak a camera with good low light capabilities and low noise at high ISO is recommended. Once you have the equipment, I would say to take it on as many dives as possible as you never know what you are going to find that will fluoresce.
I hope to work with James and collaborators at Aberdeen University in the near future, to try and understand more about biofluorescence in Scyliorhinus canicula and Raja clavata, as well as capturing some images myself!
Gruber, D.F. Loew, E.R. Deheyn, D.D. Akkaynak, D. Gaffney, J.P. Leo Smith, W. Davis, M.P. Stern, J.H. Pieribone, V.A. Sparks, S.J. (2016). Biofluorescence in Catsharks (Scyliorhinidae): Fundamental description and relevance for elasmobranch visual ecology. Scientific Reports, Nature. 6:24751 | DOI: 10.1038/srep24751
Gruber, D. F. & Sparks, J. S. (2015). First Observation of Fluorescence in Marine Turtles. Am. Museum Novit. 3845, 1–8.