Zooxanthellae questions

[davelin315]

OK, I have some questions after doing some maintenance and trying to heal up a coral that was burned a bit by my lighting. I noticed that a coral that was pink and turned kind of red in my tank has now started taking on green as well. My lights are Helios 20,000K bulbs, so I know that they are strong in the blue spectrum. Here's the spectral analysis from one of Sanjay's articles (click the chart to go to the article).

 

 

Now, the visible light spectrum, which is where the colors come from, is based on the old ROY G BIV, or red, orange, yellow, green, blue, indigo, violet. Red is the weakest light while violet is the strongest light. With a pink/red coral, the light that it absorbs is everything but the red/pink spectrum. That means that the other light is largely absorbed, hence the appearance of the reflected light - red/pink.

 

Armed with this knowledge, I'm trying to figure out what's happening and also get a general idea for what depth corals should be found at. In my case, I had a pink/red coral that technically uses all light but the red spectrum. That means that it has red pigmentation in it, hence the coloration due to light being reflected. It absorbs all other colors of light, which means that it is able to utilize those other colors. With it turning green, does that mean that the pigment has shifted or that the red has disappeared? Where can I expect this coloration to stop changing?

 

Also, based on this, should corals be placed based on their coloration? Blue corals are often the ones that are at the surface and need intense light to maintain their coloration, but don't they also occur at greater depths?

 

Not sure how much sense this makes as I'm confusing myself writing it. Anyone with a lot of physics background understand what I'm saying that can offer a logical explanation for the color shift, the type of lighting that corals demand, and how the color is indicative of the depth that the coral should appear at? Or, am I simply experiencing a lot of free green zooxanthellae in my water that is being absorbed by the corals? I'm very confused by this color shifting that's going on...

[Brian Ward]

Dave,

 

I've been pondering this for a little bit. Very interesting. I'm looking at the Wikipedia article on visual spectrum here:

http://en.wikipedia.org/wiki/Visible_spectrum

The reds are the longest wavelength of light and are absorbed first. The violets will penetrate the deepest. The spectral analysis of your bulb shows a strong spike in the violet/blue range. Violet isn't generally distiguishable between blue to the human eye, so your lights produce a pale blue - as expected.

The next spikes occur in the green and yellow spectrum areas. Of those, green has the shortest wavelength so I would expect green to be the dominant color at the bottom of your tank. Take a look at this light penetration graph:

http://oceansjsu.com/105d/exped_briny/13.html

At 20" depth, virtually all the light above 700nm has been absorbed (this is based on solar radiation so it's not exact with reference to your lighting situation but it's a good approximation). So no red light left, coral cannot be red.

You said you initiall burned the coral so I'm guessing you moved it from higher up in the tank to lower in the tank - thus pink/red initially and green now if it's on the bottom.

 

This seems to make sense to me so I think when you have a particularly large, deep tank placement based on natural coloration seems appropriate. I'd be interested to take a prism and break out the light spectrum and see what colors penetrate to where in your tank. I'm sure there are better measuring devices but I'm not sure we could get our hands on one.

[edkruzel]

Without a test we can't be certain, but I don't agree that all the light below 700nm is absorbed in his tank at the surface. While we are certain that the lower nanometers of light 400-420nm will reach the bottom of a tank, we have to remember that our glass boxes cannot compare to the real deal and while I'm not arguing basic physics I am arguing variables.

 

By statistics almost 30% of light is lost at the surface of the ocean, but that doesn't mean it loses all the red spectrum first and then yellow, green and so on... Yes red will lose its "punch" first but it will penetrate to almost a meter by minuscule and varying levels of intensity. That's really here nor there when discussing the effects on light in captivity.

 

In our small boxes of water we seldom run tanks more than a meter deep and how many run a full spectrum bulb (PAR) of around 6500K? If the water is well maintained and with the possibility of ozone it may be very clear allowing a little further penetration of light.

 

Brian makes very good points toward placement for natural effect, but how close are we duplicating the spectrum and intensity of nature? Using a 20K bulb it may be listed as a full spectrum bulb because it can produce visible light from 400-700nm but it is unnatural with spikes so high in the blue/violet range and when considering pinpoint source and intensity, it may have been burnt by an excess of the blue spectrum it couldn't shield itself from like it can with red protein pigmentation (or the ability to reflect red).

 

I ran a little experiment a few years back with a little guidance from Eric Borneman. I was living in El Paso, TX and had a southern exposure where I placed a 20L. Excessive alternating current, a large skimmer some sand, snails and some small rubble rock; no fish. I added ricodea, two types of M. digitata (green and orange) and a brown with green tipped acro. The tank ran from late April to early Sept. While the corals grew at very rapid rates they turned brown just as Eric predicted (ricordea turned a forest green) but when I removed them in Sept and placed them in a low to moderate lit tank (96watt PC's) they shown brilliant colors of reds, orange and blue almost as if on fire. After a month or so most turned to green. My point here is that we tweak the spectrum to our desire and the specimens we keep adapt, or die. Changing the Kelvin of our bulbs will enhance or detract from colors of the species we keep.

[jakaufman]

After a month or so most turned to green. My point here is that we tweak the spectrum to our desire and the specimens we keep adapt, or die. Changing the Kelvin of our bulbs will enhance or detract from colors of the species we keep.

 

 

Could you explain how the 20k bulb that davelin has would cause the coral to turn green. It seems that they turned more green in your tank with less light, maybe due to more zooxanthellae needing to be present in order to perform photosynthesis at a high enough rate?

 

Sorry if I am off on this, but its a very interesting subject.

 

Joe

[edkruzel]

That's a very good question with only educated guesses as to what is really happening with the green coloration of any particular coral.

 

Zooxanthelle are primarily brown, but green and yellow are not exactly uncommon and do not reflect or fluoresce as well as protein pigmentation when under an actinic bulb. When I referred to the 20K bulb as a possible problem it was geared towards the burning of the tissue. The real question on the coloration is if it is pigmentation or Zooxanthelle. There is so many "what ifs" associated with color change; bulb spectrum and intensity are no doubt a huge contributor, but so are water parameters, feedings and Aleopathy.

[ctenophore]

Sunlight's full spectrum is available to about 30' in nature. You can see this when diving; red objects start to look dark around the 30' mark. At 120', nearly everything is blue.

 

Photoreceptive pigments in zooxanthellae are most efficient at 450nm and 680nm, but they can use light of nearly any wavelength. Zooxanthellae don't really contribute to coral coloration other than turning the coral various shades of brown based on how dense the algae are in the coral tissue. Coloration is determined by reflective and/or fluorescent pigments produced by the coral (not by zooxanthellae).

 

A pink or red coral may be found at 100', but it won't look that way down there. It's producing pigments that happen to reflect or fluoresce that wavelength of light, despite whether or not its zooxanthellae is using those longer wavelengths.

 

So to answer Dave's color changing & burning coral question, I think what's going on is that some water quality issue or other stressor caused the coral to dump some of its zoox, causing the "burn" or bleached look. The color shift is probably due to the coral making a new pigment in response to some other cue, maybe spectrum, intensity, or even water quality. I think that the bleaching probably had little to do with the spectrum of the bulb, but the intensity could have caused the coral to dump some zoox.

 

Dana Riddle had a really good presentation at the last Macna about coral coloration, pigments, and wavelength. One thing that I remember was the idea that green coloration can appear due to other masking pigments being lost, especially in the presence of UV light. (I think) he was showing us that as certain UV-shielding pigments were lost, UV light caused what was left to fluoresce green. Basically, an otherwise not-green coral that was turning green might be in danger of UV overexposure. I really wish I could remember the details of this talk, although I do remember his data very strongly correlating with my (and several others') observations regarding green coloration in UV-shielded greenhouse environments. It would certainly be worth buying if available on DVD.

[davelin315]

I did have a water quality event in my tank when I added carbon and cleared it up too much. I lost some corals but thought that this one was in the clear... It's read and green now, only green at the base where it actually, due to orientation, receives the most direct lighting.