Light spectrum and algae growth - any scientific correlation?

[Rikko]

Hola!

I've long (loooooong) read and heard it recited without failure that the improper light spectrum in a body of water will fuel algae growth. When pressed for details, the arguments seem to break down. Doesn't anybody know?
When I was working in a LFS they usual solution to algae growth was "how old are your bulbs?"...

So is there a scientific basis for this constant well-meant advice, or is it a wash?

The closest I've been able to get to something that hits on the topic is from http://www.springerlink.com/(pjb2w2...,357,596;linkingpublicationresults,1:400459,1:

Summary Green, blue, yellow, red and white light all support spore germination whereas vegetative growth occurs only in red, yellow or white light. This indicates a requirement of nonphotosynthetic light for spore germination and of photosynthetic light for growth and cell divisions. The green or blue light is neither inhibitory to vegetative growth nor to sporulation of red, yellow or white light grown filaments. The growth promoting effect of white light is greater than that of red or yellow light. Whereas spore germination is not affected by the intensity of white light, vegetative growth increases linearly with increase in white light intensity.

This, however, doesn't explicitly include algae and the conclusion almost makes me think that spectrum wasn't even a bit part of their experiment.


Does anyone have any comments either way?

 

[hahnmeister]

Well, I can tell when my bulbs need to be changed not only by coral growth, but by the microalgae that tends to pop up.

I had an algae problem because my 10,000Ks needed changing, but instead I used 20,000Ks. All other parameters were kept the same, and the algae went away just like that.

Using a halogen bulb with lots of yellow seems to make algae grow like mad.

Plants and algae are green most often, this means that they absorb the red and blue and leave green to be reflected.

Corals are more used to blue spectrum the deeper they are, so I try to use bluer bulbs as the yellow spectrum seems to be a waste unless I want to grow algae. Some argue that PAR is PAR, and corals dont care what the spectrum is as long as they get it. I dont agree with this. Corals under 10,000K vs. 20,000K most often change their pigments. This suggests they are aware of their spectrum. Now, corals are mostly used to bluer spectrums, so I would conclude that bluer light is more useful for corals than yellow/red. And if corals were nothing more than 'sophisticated plants' like many suggest with the idea that PAR is all that matters, then they wouldnt change their pigments under different spectrums of light. And at that, algae seems to prefer yellow light to blue, so if even algae notices, why wouldnt a coral also prefer certain spectrums? I notice better growth with bluer bulbs, even if the PAR is lower, than with a whiter/yellower bulb.

There are two main areas for photosynthesis in the light spectrum. I cant remember all the details off the top of my head, but I remember plenty of research being done on land plants and the find was that their chloroplasts do prefer certain spectrums. Well, if plants, not even in the animal kingdom, can 'prefer' certain spectrums...why wouldnt corals?

A popular bulb with coral farmers is the 1000watt halide, but they take it in the 20,000K version over the 10,000K...kind of odd considering all they want is growth and 10,000Ks have a higher output...eh?

Ill dig around and see if I can find that plant data, but I do think that spectrum counts just as much as PAR.

 

[hahnmeister]

Here is a tidbit from what I remember. It points out that many reef organisms are not Chlorophyll based, but can get their energy from outside what we would consider the normal PAR range (IR). Red light is primarily for budding, and blue light is mostly for growth in plants. If anything similar to this carries over into corals, it means that corals would grow better under blue light...so a bulb that has more PAR in the blue spectrum could outperform one with less blue but higher PAR including reds and yellows.

Many might scoff at this and say "well, the iwasaki 6500K is the best for coral growth", and its very yellow with little blue. Well, it does look yellow to the eye, but if you check its spectral plot, it contains more 420nm and 450nm (and everything even close in the blue range) than most any 10,000K or 20,000K. We simply might be overlooking that because of what we see with our eyes, but all the coral might see is all that blue, and decide to reflect the rest...which would make sense considering how corals tend to 'brown out' with their pigments when under lower K light.

The shift of a bulb as its burning out is often towards the red spectrum...and if you have a 10,000K, that can mean a raise in the IR output to unusual levels...which is what many blue, red, and purple algaes can use.

Here's the 'tid-bit'...
http://www.answers.com/topic/photosynthetically-active-radiation?gwp=19

And here...
http://www.answers.com/topic/photosynthetic-pigment?gwp=19

I suppose the 'penultimate' experiment would be to use a 10,000K over one tank, and some radiums over another, matching their full-range PARs with a meter (multiple radiums and one Iwasaki). The overall PARs would be matched, but the radium or 20,000K bulbs would have a huge advantage in the blue range.

The catch is, and this is perhaps the basis for the argument that PAR is PAR, is that many 10,000Ks have 450nm peaks that are greater than many 20,000Ks, even though the 20,000K will have a larger 420nm peak. So even though the bluer bulb might be the right idea, it just happens that the 10,000K makes up for this lack of a visible blue by having a huge purple (450nm or actinic) range to make up for it. So to disprove the idea that PAR is PAR, the 10,000K bulb would have to have its 450nm range filtered out as well...and then the PAR's matched up again. The results would prove what are the most valuble spectrums for coral...and I would suspect that blue & purple play a much more useful role than yellow and red (green is pretty much useless for any photosynthesis...but oddly enough it does get counted as PAR, think about that and what it means for the whole PAR is PAR idea).

What I am suggesting is that perhaps a bulb's PAR for our reefs should only be compared from 400 to 500nm. When you look at it this way, the 450nm spike from a 10,000K and 420nm spike form a 20,000K, as well as all the other light in this range, begins to look the same...with some slight differences between two similarly useful spectrums (420 & 450nm). This would mean that the very idea of "PAR is PAR and that's all that matters" would be incorrect, but from the standpoint of comparing a 10,000K to a 20,000K...things might end up pretty similar, and PAR readings for 10,000Ks would be more in line with their 20,000K cousins which often seem to be able to grow corals just as fast if not faster despite the lower PAR. This would also explain why such a yellow bulb like a Iwasaki 6500K is still such a great grower...as its PAR from just 400-500nm (blue range) is still more than most bluer bulbs.

 

[Cody Ray]

Wow, that was very well put!

 

[BeanAnimal]

I think the very simple answer is that different organisms thrive under different lighting conditions. There is a lot of science to show this. Certain corals do better under certain lights, as do certain plants, algea and anything else photsynthetic.

Bean

 

[Skepperz]

I thought this was quite an interesting article regarding lighting and corals.

http://reefkeeping.com/issues/2004-08/ac/feature/index.php

 

[mwcf]

I am deeply disturbed at the common theme within the post to this thread. There seems to be some discussion of the differenences between what algae might prefer in a light source vs. what a coral might want from a light source.

There is a fundamental misunderstanding here. Corals only "care" about light because they have algae living within their cells. Past that, they have no eyes.

Point is... the true beauty of corals is that they are animals dependent on plants to such an extent that they are clearly the first "generation" of animals. The very first sign of plant life evolving into animals...

Anyway, corals are not photosynthetic. The algae living symbiotically within their cells are. Just as the bacteria that live within us are a necessity for our existence but I consider myself at least a little different from them.

 

[hahnmeister]

Um, mwcf, I think everyone here knows that corals have symbiotic algae and that is what needs the light, not the corals. Sorry we didnt post that clarification to avoid concerning anyone who might question how we understand coral biology...but its a given to most here. We are just trying to keep it simple and saying that the corals need the light...since indirectly...they do. We aren't being technical because we already know this as a given. Its the same as if my response to you was that its not the photosynthetic cells within the coral that need light, but the chloroplasts within these cells that do. Picky picky picky...lol. I think you are reading too much into this.

http://www.advancedaquarist.com/2006/1/aafeature1

At that, the reason we do say corals themselves, and not just the algae cells that they contain is because its not just the algae cells that react to light...the pigment cells do as well. And in that respect, corals do 'see' to the extent that they can change their coloration to more suit the type of light they are exposed to. It might not be done with compound eyes or lenses, but the photoreceptors within the corals cells do react to changes in spectrum as well as intensity.

When you ask someone here for advice on how to light your tank, you dont ask "how much light should I provide for the algae inside the mantle of a crocea clam?" You do ask "how much light do I need for a crocea clam?" And clams in fact do have 'eyes' FWIW.

The main Q here was something like "does spectrum matter or vary between various photosynthetic organisms and corals?", and the clear response is yes. There are certain species of algae that only use IR spectrums for growth so they can exist without competition. Plants use blue and red spectrums, but for two different functions, and the algae within corals most likely also responds to certain wavelengths more than others...and considering the variety of these types of algae as detailed in the latest issue above, these spectrums most likely also vary from coral to coral as well. Sometimes people say that all that matters is PAR, which is a measure of a light source's spectrum from about 400 - 700nm...but the funny thing is that a high PAR bulb that might be very green would be less usefull than a bulb with the same PAR with a very blue output.