P.A.R. Values and Zooxanthellae

[Diver_1298]

I wanted to start a new topic on the P.A.R. value of lamps and how it affects Corals with the symbiotic algae zooxanthellae. I hope to clarify some questions that were confusing me and maybe help someone else understand the process also. I know from links like these that not all lights are created equal, they have different P.A.R. values. So to start it off...
1.) What is PAR? (Laypersons terms)
2.) What are the Values of PAR?
3.) What should we look for in our reef lighting and while doing some research maybe dispel some myths about reef tank lighting.
P.A.R. for dummies (sounds like a book title) - A measure of visible light intensity using an instrument calibrated with daylight. Right now I don't think the units (µMols•m2•sec) it is measured in are important only that there is a high maximum value and a low minimum value. The highest value that can be recorded is 2100 for outside solar radiation.
If we look at this link http://www.advancedaquarist.com/issu...03/feature.htm to some par values taken in some marine aquariums it looks like a high value is around 700 (sps coral tank) at the top of the tank and 75 for a low at the bottom of the tank.
Visible light is supposed to be somewhere between 400 nanometers and 700 nm. This is the light we are able to see without any devices (the naked eye). The low end being the blues and violets and the high end, a reddish color.
Photosynthesis which occurs in the Zooxanthellae is supposed to happen because of this band of visible light. The Zooxanthellae provide nourishment to the coral and in some sps corals this is 99 percent of their food source.
Now for some questions, if a 6500k metal halide bulb has a higher par value than a 20000k metal halide bulb, is it better for your Zooxanthellae and therefore better for your corals?
Is there a wavelength in the visible light spectrum that promotes more photosynthesis than another? If so, is the PAR value the final answer to our reef tank lighting questions.
How much light is too much light? A par value that is detrimental to zoox and photosynthesis? And along the same line what is an optimal value for PAR?
Maybe another thread for this one, Cynobacteria or other Algae’s, what wavelength do they thrive under and is it the same for the Zooxanthellae?
I would appreciate anything that you have to contribute, or questions you may have.
Jim

[Matt Rogers]

This stuff is really out of my league - I just look at PAR as INTENSITY.
But you did ask how much is too much and there does appear to be a saturation point at coral can't absorb any more, check this out - Photoinhibition.

[Diver_1298]

Thanks Matt,
That is a fantastic link on PAR and photosynthesis. [smiley=2thumbsup.gif]
It does answer some questions and raises others. It does say there is a saturation point but I don't see a value or number where that occurs for corals. It also points out that the spectral composition is important for the different types of photosynthetic pigments but again I didn't see any specific wavelength??
Are there any Brainiacs out there that can help out on this?? Mike, David...anyone else, Jason?
Thanks,
Jim

[Speedy]

I would say that it would depend on the species.just a guess. Will do research , and get back to you.

[Gresham]

Nice link Matt, leave it to Steve Ruddy to put up such great info.

[Diver_1298]

OK, after further research and more reading. I never knew there were so many colleges and thesis papers on the net. Without stealing anyones work I can point to some links http://www.personal.psu.edu/faculty/...osynthesis.htm *One of the interesting items pointed out in this article is that the absorption spectrum that *takes place in zooxanthellae has a broad peak in the 400 to 500 nm band. And corals with different types of pigmentation will use slightly different wavelengths. There is another paper that used a 6500k Iwasaki bulb *that has a high par value but most of its light is in the higher band 500 -700 nm. They said it was one of the best bulbs to use but imo it sure isn't nice to look at. So for some broad conclusions. You need a light with good PAR values if you are planning on keeping sps corals. And most of the information on bulbs and par values is found by researching on the net or buying your own meter and measuring the par values for your self. The spectral wavelength of light between 400 and 700 nm is necessary for photosynthesis, but trying to find a bulb with a good par value and with the proper wavelength for what you might consider important for your corals can be a daunting task and probably unnecessary. Not too many people have one type of species specific coral all at the same tank depth with the same the wavelength requirements.
Jim
Feel free to correct any erroneous errors or add supplemental information.

[Diver_1298]

After even more research I have found an interesting web site that states that the wavelength that is used for "plants" not corals, peaks in the 420 nm band and the higher 670 nm band. This is a must read for this thread because it touches on all the points already made and the relationships between them. Even though it is not zooxanthellae specific. Take a look
http://www.aquabotanic.com/lightcompare.htm
Jim

[mojoreef]

Good thread!!
Par is basically the color/temp range that the corals zoox can use for photosynthesis (goes back to our pigment conversation). So not really intensity but more a measure of light temp that corals and other things can actually use.
The light produces photon energy which the zoox have the ability to capture and transport through their eletron transport system (think of it as a highway) the energy then goes to the electron transport center where it is converted to sugars, carbs and so on that the coral an use for tissue growth. Of coarse the waste from the coral travels back to the zoox for it to use the same way.
Their comes a point where the coral must control the amount of product it is getting from the zoox. To much photosynthesis can create O2 which when mixed with other chemicals in the coral can create a super oxidizer which will eat the corals tissue and kill it (quickly to). Now the coral does have enymes that it releases to combat this oxidizer but the side effects are not healthy for the coral.
The coral regulates the zoox byproducts in a few ways, shutting down the hiway, closing zoox saturated tissue and so on. This is what folks call the point of diminishing returns. SO basically the coral will take in only so much light until it has all the food requirements it needs and then it will begin to slowly curve down the amount of photosynthisis until the process becomes completely stopped.

Anyway kind of a rough explanation of the top of my head, hope it doesn't muddy things up any more.


Mike

[reef_guru]

I just look at PAR as INTENSITY.

(lux or lumen) is intensity
(colour or usable light) is par
Advanced Aquarist's Online Magazine - Lateral Lines: Classification and Terminology For Reef Aquarium Lighting

[onecansay]

Great thread. Good to see discussion on this most important issue. I also wonder once light has been solved does movement of water play a role in this. The more movement, the more refraction of light. Surface tension will also create another light issue. Particulates in the water would also have to be taken into consideration. Muddy waters indeed!