Seeing red at 60 feet

[Crush]

I found a reference on fluorescence (see here). It says, in part:

SCUBA divers rediscovered fluorescence in the 1950's. Luis Marden, a photographer for National Geographic magazine, wrote in 1956 that he noticed red anemones at a depth of 60 feet, where there should have been no red. The red color disappeared in flash photographs, and Marden correctly concluded that the effect was due to fluorescence.

So, according to the above, in order for what I saw to have been fluorescence, the red should have disappeared in the flash picture. Since it didn't, back to square one.

I keep agreeing with Matt S. Bioluminescence requires the organism to expend energy while fluorescence is passive, relying upon ambient light of a different wavelength. Unless the organism lived in an extremely low-light environment I believe that bioluminescence would be a waste of energy, especially if it would also not aid in procuring nourishment, procreation, or avoiding predation.

I disagree with Luis Marden's conclusion that the animal was not fluorescing because the red colour disappeared in flash photographs. Shining additional light on a fluorescent surface will never lessen the fluorescent light emission - his argument has no basis in science. Additional illuminating light may make the fluorescence less obvious by bringing out other colours, but the fluorescence will in no way be quenched. However, if you were to photograph this organism it might appear that the fluorescence magically vanished - the fluorescent light is still there, but so are many other colours, and since you had to close down your aperture to avoid over-exposure, it would appear that there is less fluorescent light. Try this experiment - shine a black light on a white T-shirt in the dark - it will fluoresce. Heck, mix yourself a gin & tonic - the quinine in the tonic water will also fluoresce in the dark in the presence of a black light. Now, black light in hand, go outside and repeat the experiment on a bright day. The fluorescence is still there, but you just can't see it because the reflected non-fluorescing light is now much brighter.

FWIW, fluorescent pigments absorb a range of wavelengths of light and re-emit that light at longer wavelengths over a range. The object might appear to you to have one red colour, but in fact it might be giving off light which ranges from orange to deep red.

 

[Crush]

I ran a quick calculation on the attenuation of light by pure water (which will not account for any particulate scattering). At 60 ft the relative decreases in light (relative to what was originally present) are:

700 nm (red): 1/140200
580 nm (green/yellow): 1/6.5
450 nm (blue): 1/1.8

So, there is about 80,000 times more blue light at 60 ft than there is red light if the sun were to emit blue and red light in equal proportion (this is not the case).

 

[BioLogic]

Bioluminescence bright enough to catch your eye like that would be pretty unusual, I bet. It has to compete against quite a bit of ambient light still... that is a lot of power output. My guess is a fluorescent process. Nice find.

Virtually none of the ambient light is red ... so the red-sensitive cones wouldn't be suffering a competitive effect. And look how effective it was at catching attention; that's a great evolutionary pressure for developing a strong bioluminescence. My hypothesis would be bioluminescence, given how common that is at depth... but I've been wrong before.

 

[Crush]

...that's a great evolutionary pressure for developing a strong bioluminescence. My hypothesis would be bioluminescence, given how common that is at depth... but I've been wrong before.

How common is bioluminescence in the daylight zone at 60 ft? I can't find a single example...

 

[gzscuba]

I've got to agree with mpetryk. The amount of energy that an organism would have to burn to compete with daylight would be absolutely enormous. When you perform biological assays involving luciferase (a bioluminescent protein), generally the container is colored white so that any light produced gets bounced around the container (or plate) into the detector. That little bit of light is precious.

In contrast, you use a black container with fluorescence measurements to decrease the extra noise.

Also, keep in mind that (up to a point) the amount of emitted fluorescent light will be proportional to the light absorbed (so fluorescence will be large during the day).
For the interested reader, it looks like red fluorescent proteins used in biological imaging experiments came from corals in the genus Discosoma. Take a look at:
Biochemistry, mutagenesis, and oligomerization of ... [Proc Natl Acad Sci U S A. 2000] - PubMed result

-Greg

 

[knotical]

Here are a couple of articles that support the notion that it's fluorescence.

The Fascinating Phenomenon of Coral Fluorescence
Charles Mazel on Coral Fluorescence
Lord Howe corals light up cancer fight › News in Science (ABC Science)

 

[Mooseman1007]

An Interesting factoid that you may or may not know, but the Nobel Prize was awarded to Roger Tsien for his work on the development of Green Fluorescent protein originally isolated from the Aequorea victoria jellyfish. The Nobel Prize in Chemistry 2008
Rogers work has seen him modify the protein to encompass almost the whole spectrum of colours.
Interestingly red fluorescent proteins are excited best by light in the 450-550nm spectrum (blue/green) so this tallies well with the available light at depth.