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Photosynthetic Saturation and damage of surpassing

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Macbeth417

Reef Monkey
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Oct 18, 2003
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Seattle, WA
Okay I really need some brain storming here or at least some people to point me at information.

AKA: Johnny 5 needs more input.

How much light is "too much" light? At the point where a coral (lets say shallow to mid-water Acropora for this topic) reach thier photosynthetic saturation level and then the light source continues to bombard the coral does it become detrimental to the coral? What are the long-term effects, how does color and pigment relate and what are some rules (opinion) of thumb for the respective growth forms and colorations of these Acros.

I noticed that anything in purple or blue range tends to do great up high, as many have anecdotally noted, and the reds/oranges do fine in the middle area. Greens maybe middle to high depending on the shade. I have noticed some darker greens etc. will tan out when very high up (6-10) below a bulb (in my case 10kk DE 250watt XM on PFO HQI ballast). Could there be too much light (heat could be a culprit, but I would like this to stick to impact of light)? I'm trying to track down information on this and would really love to hear your thoughts folks.

Articles, books pages, personal experience. Anything here would be of great help.

-Erik :D
 
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Macbeth417

Reef Monkey
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Seattle, WA
In his book Aquarium Corals, Eric Borneman discusses the benefits of imposing varying, and more natural, photo intensities as well as the danger of oversaturation. He writes:

"The use of varying light intesities over the day has important implications. The consistently "clear" days over our aquariums is unnatural. Corals exposed to artificially intense and unrelenting light may begin to experience oxygen toxicity from the oversaturation of coral tissue with photosynthetic oxygen. In addition, corals that are exposed to sudden and dramatic increases in light can have thier zooxanthellae produce more oxygen than can be consumed..."(Borneman, 334).

He follows with a short discussion of the enzymes our corals may produce as a result of these excess levels of oxygen:

"... the production of enzymes such as superoxide dismutase and peroxide may literally destroy the coral tissue in an attempt to cope with the free oxygen radicals and peroxides endangering the corals. The enzymes secreted by the algae and the coral in an attempt to control these radicals can be overwhelmed and light shock or oxygen toxicity is the result. Corals may then begin "bleaching," ... It is strongly recommended that ... prolonged periods of very intense light be tempered with some "breaks" of intensity throughout the day"(Borneman, 334).


Well that sheds some light (hah!) on the topic as that is what the coral that initiated this itnerest seems to be suffering from. It has great growth and good poylp extension, but seems to be slowly bleaching (over the course of almost 3 months). So perhaps it not mearly the intensity of the light but also the consistancy of those light level. I will try to add a stormy day every week or so and see what happens.

-Erik AKA: Johnny 5

Source:
Borneman, Eric H. Aquarium Corals Selection, Husbandry, and Natural History. New Jersey: T.F.H, 2001.
 
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Macbeth417

Reef Monkey
Joined
Oct 18, 2003
Messages
563
Location
Seattle, WA
Another small section from Borneman that touches on the subject states:

"The rate of photosynthese rises in corals with increasing light levels, up to a maximum rate at the so-called saturation level of light. The saturation level of most symbiotic coral in shallow waters is at least several times lower than the photo syntheically active radiation at the surface, or PARS.
This means that, above a certain level of irradiance, photosynthesis rates (and all the processses ofa coral that are light-dependent, including metabolic rate, calcification, ect.) will not be incresase by higher light levels. While many aquarists and writers have been concerned about the difficulty of replicating the intesity of sunlight on shallow tropical reefs, the fact is that many corals can reach thier maximum rate of photosynthesis in light that is much less intense than that provided by tropical sunlight. In fact, studies have shown that some corals that depend on light to a greater extent, such as Tubinaria species, Seriapora species, and Merulina species, may have higher photosynthesis rates in moderate light than in strong light”(Borneman, 51).

I am going to lower my Seriapora (which is small and growing like mad these days, but is still very close to the light source) and see what differences I notice. I am going to do the same with one of my Acros. I will snap some pics and docutment this over a few months as I am interested to see the results.

-Erik

Source:
Borneman, Eric H. Aquarium Corals Selection, Husbandry, and Natural History. New Jersey: T.F.H, 2001.
 
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Macbeth417

Reef Monkey
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Oct 18, 2003
Messages
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Location
Seattle, WA
Well according to Elmo, the new Corl Magazine has an article that pretains to this topic. I'm going to see if I can't track down a copy today and see what there is to be learned.

-Erik
 

Elmo18

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Aug 5, 2003
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Yup, its in the Coral Magazine that just arrived here in the states not too long ago. Used to be called Koralle in hmm yeah Europe where it was first published and circulated.

I saw two diagrams there while visiting Below Sea Level about the cycle that involves zooxanthellae, CO2, and sunlight, etc. Ask Dan or Chris if you can see the mag.

- Elmo
 
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