Diving For Science 2005 Proceedings Of The American

Diving For Science 2005 Proceedings Of The American Academy Of Underwater Sciences
In the water you use your normal dive light to navigate to the work area and orient yourself,
then turn the white light off and switch to the excitation light. Often when you do find
something that fluoresces it will not be obvious what it is, and you will be switching back
and forth between your white- and excitation-light sources.
Photography
Just as for conventional nighttime photography you use your dive light to find subjects of
interest, then use your electronic flash to take the photograph. A conventional electronic
flash can be adapted to be an excitation source by the addition of an external filter. A barrier
filter will be needed over the camera lens. Figure 4 shows an example of filters that can be
used with an underwater camera and strobe. For fluorescence photography you will
generally need to use relatively high speed (ISO 200 or more) film, or a high ISO setting on a
digital camera. Even then you will need to shoot at relatively open f-stops, from f2.5 to f11
depending on the brightness of the fluorescence.
Figure 4. Nikonos V underwater camera and Ikelite
underwater flash, showing the barrier and excitation
filters that would be used with each.
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Videography
The technique for videotaping fluorescence
is along the same lines as described above
for diver viewing and photography. The
main ingredient is an intense light source to
excite the fluorescence brightly enough to be
recorded.
What fluoresces underwater
Fluorescence has been discovered in a wide
range of underwater life. Very few people
have really undertaken this kind of
investigation, so we have still barely
scratched the surface, and much more
remains to be discovered. The following summary should not be taken as a comprehensive
listing, but just as an overview of what has been learned to date.
Algae
The fluorescence from photosynthetic pigments in marine algae has been known for a long
time. Chlorophyll emits red with peaks at about 685 and 730 nm. Phycoerythrin, an
accessory pigment in the red algae and cyanobacteria, emits orange with a peak at about 575
nm. This fluorescence is widespread in shallow-water environments, and can be used to
photographically map the distribution of the algae. Many corals and other reef cnidarians
contain symbiotic algae (dinoflagellates) and will exhibit the same red fluorescence as the
macroalgae, although usually with greater intensity.
Invertebrates
We have found fluorescence in most invertebrate phyla. Sponges (Porifera) do not tend to be
very fluorescent, but in shallow water they often have associated cyanobacteria that