This is a VERY good read!
Just took a peek, looks very interesting. this will make a good throne read later…better head to taco bell lOl
thnx tim. great clam info, basically saying there is NO saturation point of too much light for tridacnas. YAY!
The one critique for which the article doesn’t account for are the multiple zooxanthellae strains contained within the perspective coral tissues. I am sure they all follow the c3 photosynthesis pathway which would have a degree of saturation. But taking this into consideration the amount of light required to saturate would be highly variable from species to species and even from specimen to specimen. Also, plants can readily adapt to numerous conditions; even too much light.
http://cropandsoil.oregonstate.edu/wheat/CSS330/Biomes_Psyn%20Notes.pdf
http://ehleringer.net/Jim/Publications/352.pdf
Results
The results suggest that corals’ zooxanthellae exhibit a broad, but sometimes limiting, range of photoadaptive capacities.
The author touches on this notion, but doesn’t specifically elaborate. He does mention in the conclusion the adaptive strategies to the varying low light conditions. But dismisses the adaptation of reflective pigments by the hosts. Obviously,further scientific study is warranted pertaining to endosymbiant photosynthesis in home aquaria.
well, they were measuring photosynthesis. not color. when a coral is getting too much light, they self shade with more brown zooxanthalae to shade the pretty pigments we want to see. so the coral browns out instead of coloring up. or so i think it says.
Using too generic of terms here talking about a very complex topic. If Zoanthids get too little light they lose color… because they spread out as wide as possible trying to catch as much light as possible. Ok some might say Zoanthids aren’t try corals, but Euphyllia and Fungia will do the same thing. I’ve seen Fungia grow to 6-7 times their normal size when the sun doesn’t rise in the morning and they figure they’ve been shaded out so they better expand and figure out where the light is and move, but they just never find it.
Don’t forget it isn’t just Zooxanthalae that affect color or “pigmentation” and that isn’t the only thing corals adjust based on relative lighting levels. Florescent pigments…
This topic can easily lead into philosophical arguments as well. How do you know your coral is, “happy”? Could open up a whole new board on the forums to discus that one. 
well, the coral might be happy by just browning out with sunscreen. but the reefer wont be happy, looking at it. we dont like their sollution to too much light.
This topic has interested me and I’ve been doing some research…
http://www.springerlink.com/content/u06501589670j067/
Apparently protein and tissue structure will alter in combination with zooxhanthellae after exposure to Higher UV radiation.This would be tantamount to the florescent pigmentation Jon spoke of.I have also read that the mucousal layer will become more pronounced with certain wavelengths of electromagnetic radiation. I am assuming this is related to the brown coloration typically experienced.
Nah the mucosal layer is just about perfectly clear. That’s the crap you get on your fingers when you pick the things up out of the tank. It makes perfect sense why the layer would get thick as more radiation hits it. Same reason an aquatic organism can survive being exposed at high tide for hours. “They slime over”. It might give it the slightest little brown tint, not sure, but not what hobbyist are fussy about or complaining of.
There are two extremes that cause browner color. Down deep corals spreading out to capture more light just have everything spread out further.(like adding water to water color paint) In addition a lower concentration of zooxanthellae and higher focus on predation often occurs. The other side of the coin I would guess has to do with not only the strength of light, but the spectrum. If you keep the same amount of PAR locked on a particular coral in your tank, but shift to a blue spectrum you’ll see bright colors right away AND in time the concentration of certain zooxanthellae and fluorescent pigments will shift to brighter colors.(when you change bulbs your corals look different right away based on what is reflected to your eyes and in time because the coral is adapting to conditions)
Why are wild collected acros often browner in colors. They are often collected from wading distance where there is just about a complete spectrum and not just blue. How about Dr. Mac’s green house? His tanks aren’t deep either and he isn’t using blue bulbs he is using sunlight with a more complete spectrum.
Haven’t read hard core on the topic most of the above from experience and talking with people in the industry that actually know what they are talking about.
Interesting, thanks for the insight.
Like I said more anecdotal insight then anything.
PAR is what we measure but it is PUR (photosynthetically usable radiation) that is what really matters. Coral, or its hosted algae i should say, doesn’t care about the color… it is the wavelength of the photons striking it that matter and the most PUR occurs in the 420-460nm which just happens to be blue. The reason they fluoresce is saturation, if they reflect light they are not using it for photosynthisis. 700nm spectrum has much less PUR for zooxanthellae so they reflect less and look brown while making the most of they PUR to photosynthesize.
Not all corals are the same though to each have different saturation points.
This is what I understand of it anyhow.
Photosynthtically Available [or Active ] Radiation
not Usable
that’s what i come up with for the acronym
Here is additional info that I think is a great read.
http://www.advancedaquarist.com/2005/12/aafeature2
from that article.
“The biological mechanisms in place during the luminous phase of photosynthesis do not depend on the photons’ energy, but on their number. This is exactly what the Einstein displays. The PAR (Photosynthetic Available Radiation, unit µE/m2/s) measures the number of photons reaching a surface, all this in the wavelengths of the visible light (between 400 and 700nm). It is indeed in this portion of the spectrum that we can find the different absorption peaks of the photosynthetic pigments. As these pigments do not absorb energy in a equal manner on all that 400-700nm range, but only at certain precise wavelengths, some prefer using the PUR (Photosynthetic Usable Radiation) in order to quantify the number of photons truly used by the photosynthetic cells. The PUR is thus defined by the light source (emitted spectrum, intensity) and by the studied pigments (because of their absorption spectrum). This one is probably better left to specialists…”
[quote=“moliken, post:13, topic:3559”]
Photosynthtically Available [or Active ] Radiation
not Usable
that’s what i come up with for the acronym[/quote]
Another reason why PAR could be irrelevant in terms of coral homeostasis . It really depends on the wavelength of radiation reaching the corals. PAR could be a good indication of total radiation emitted by a light source, but not actually usable by the zooxanthelllae.I skimmed that link Tim, you can borrow my old physics text book if you want, it covers a lot of information contained within that article.
I’ll take you up on that Andrew, I have nothing but time in the winter and I like to read science articles/books, Astronomy as well.
If i don’t make it to the holiday dinner, I’ll bring the book to the January meeting.
there is a concurrent thread on RC in the advanced section. The OP holds the same opinion expressed here regarding the irrelevance of PAR for coral in the home aquariums.
I never stated PAR was irrelevant.
I finally got around to it… it was long, and painful to get through :-?..but the article was good reading lOl