Using UV-A to promote pigmentation: advice on the subject

[BrainVat]

This picture was taken under a phillips 40w blacklight. UV-A stimulates defensive pigments that show nicely under 20k and 10k lighting. I speculate that supplementing a little extra UV-A each day results in greater expression of these defensive pigments by corals and/or their zooxanthellae.


http://www.canreef.com/photopost/dat...owing.jpg?9973

This LPS coral was mildly fluorescent when I first put the light over the tank. After about 30 minutes of UV-A, it glowed much more strongly. I suppose the effect is comparable to a tanning salon, except that corals have adapted far more numerous pigments for dealing with UV-A rays.

Also, an anemone did not fluoresce at all when first exposed to UV-A, but its tentacle tips began to fluoresce after less than an hour of exposure, and increased steadily in intensity for some time after that.

If you are planning on trying this, you must acclimate your corals to the UV-A by a tiny bit each day (20-30 mins), and should only try it on corals that are naturally adapted to make use of UV-A, such as deep-water LPS. If you turn on a blacklight over a coral and it does not fluoresce immediately or takes too long to adapt, chances are it is has little capacity to make use of this light and may be threatened. Even once a coral has produced the pigmentation needed to protect itself, you still will only provide a few hours of UV-A per day to maintain these pigments.

Realize that some corals do not produce these pigments purely for defense. The re-emission of light at a higher wavelength allows that light to be captured and used for photosynthetic purposes - perhaps even a driving force for the symbiosis between deep-water coral and their zooxanthellae. The former could produce the "UV harnessing pigment" while the latter catches reflected, lower-energy light and photosynthesizes.

Evidence for this comes from anecdotes in the hobby, where people have claimed to witness improved coloration on the switch to radium 20k bulbs, which emit stronger UV-A than other leading brands in the 20k range.

I am still in the process of experimenting and haven't decided whether to use this light regularly or not. It would have a strong impact on the selection of corals for my tank, which are mostly brains and hardy, deep-water LPS anyway.

-B.V.