Coral growth and light spectrum

[cilyjr]

I was recently at a fellow reefers home (he may chime in if he so desires)and we got to discussing lighting. I had been doing some reading on lights and was thinking on the necessity of the so called "full spectrum" LED. I don't want this discussion about that though it was just what got me thinking.

For a long time I was told by many an experienced reefing hobbyist that corals look better under more blue lights in the area of 14 to 20k but grow faster under lights in 10k range. I took this as fact. I had however recently with the help of above mentioned reefer, began to think about photosynthesis. It is making me rethink my inherited beliefs.

So to the meat of it. Photosynthesis primarily takes place at about 400nm with another spike in the 650nm area. If sps coral growth is fueled by the amino acids and glycerol that are byproducts of the photosynthetic process and if photosynthesis is primarily happening in the blue area of the visible spectrum would not a more blue light help to spur coral growth?

 

[dannyp02908]

I think (I'm no expert btw) the issue with the more blue light comes to intensity. If I recall, the blue light is far less intense. But I have also read some of the photosynthesis charts and lean to agree with you on the spectrums that appear necessary.

Also, my guess to the 10k growing coral faster is that it provides both the blue and red spectrum spikes. Not just the blue.

 

[wpeterson]

I am new to the hobby, so take my experience with a grain of salt.

I began with very white lighting (10k) with small actinics but didn't have good growth. I switched to much bluer, brighter Kessil A350 lights and have had dramatically higher growth. This improved the spectrum and overall light output. There are many variables here, but that was my experience.

For example, a small three headed ReefGen Zoa frag maintained itself in place for over a month under 10k LEDs, but grew 4 new heads in one month under the Kessil blue/full spectrum lights.

It's important to have both enough light output, but also appropriate spectrum. Your mileage may vary.

 

[Pat02026]

Had a little insight on a similar thread a year or so ago....
http://www.bostonreefers.org/forums...ir-affect-on-colors&highlight=Colors+spectrum

 

[RMc]

Growth will be just fine under blue/white led's. Full spectrum is for aesthetics and potentially pigmentation. Something to look out for with LED's is actually having too much light. This can be especially true if you have narrow spread lenses on each led. Because a blue/white system emits less total visible energy they can look a lot dimmer than a halide / T5 putting out the same amount of photosynthetically active radiation.

But yeah, for growth driven by zooxanthellae energy production... I'm sure Blue / Neutral white is fine... it will just look like crap.

Pigmentation is still an open debate as certain pigments may be produced in response specific wavelength exposure (UV / greens).

 

[RMc]

Just something else to keep in mind. This graph shows how light is attenuated as it passes through water. You can see that far UV and IR are filtered almost immediately. If one were to supplement Blue/white LED's - Cyan (500-520) and violet (380-420) would probably be the most important.

 

[cilyjr]

Full spectrum is for aesthetics and potentially pigmentation.

I am unsure. Tanks with only 10k bulbs look almost gold.(I understand this is also often a result of too much DOC build up). But I suppose that is an aesthetic preference. Though it is exactly opposite what was commonly believed only a few years ago.

Because a blue/white system emits less total visible energy they can look a lot dimmer than a halide / T5 putting out the same amount of photosynthetically active radiation.

Very true

But yeah, for growth driven by zooxanthellae energy production... I'm sure Blue / Neutral white is fine... it will just look like crap.

I disagree as corals say stylophora for example in very shallow water say 10m are so all look brown whereas they seem to show much more colors when one gets into the 25m or so.

 

[cilyjr]

Had a little insight on a similar thread a year or so ago....
http://www.bostonreefers.org/forums...ir-affect-on-colors&highlight=Colors+spectrum

Thanks I will look through this in the next day or so

 

[cilyjr]

I began with very white lighting (10k) with small actinics but didn't have good growth. I switched to much bluer, brighter Kessil A350 lights and have had dramatically higher growth. This improved the spectrum and overall light output. There are many variables here, but that was my experience.

For example, a small three headed ReefGen Zoa frag maintained itself in place for over a month under 10k LEDs, but grew 4 new heads in one month under the Kessil blue/full spectrum lights.

Interesting but as you said too many variables. The most obvious I see is that since coral grows out from the tips the more tips or heads you have the faster they grow. So if you had a new tank and a certain light and an lps coral with 1 head it will divide in to 2 but the next time 2 divide into 4 so growth seems slow. Now you have 4 heads and one changes the lights but 4 heads are ready to become 8 so the growth rate has increased dramatically.

It's important to have both enough light output, but also appropriate spectrum. Your mileage may vary.

Yes but what is the appropriate spectrum?

 

[cilyjr]

So here is a little bit more I found interesting over the past few days. I found an older article (pre led) that suggests corals will gather the light they need regardless of spectrum. Favia was used in this experiment.

"This experiment's results suggest information potentially valuable for hobbyists - that rates of photosynthesis were essentially the same under these two distinctly different light sources. Other than aesthetic value, there appears to be no advantage, photosynthetically speaking, in using high Kelvin lamps." Riddle feb2002

Another paper I found that was exploring the adaptability of coral and spectral light (not really what I am exploring in here) suggests that stylo specimens collected at different depths respond differently to lighting of different spectrums at least at first. I feel this more stresses the importance of acclimating corals to new lighting rather than proof of optimal growing conditions.

"There was a clear and significant relationship between colony depth and photosynthetic performance under blue light spectra. Deep corals showed higher photosynthetic performance when they were exposed to blue light in comparison to full PAR illumination under the same light intensities" J.E.B oct 2010

.

 

[jfourn83]

Good stuff Chris

 

[RMc]

Another useful article on light spectrum: http://americanaquariumproducts.com/Aquarium_Lighting.html

 

[cilyjr]

Thanks I will check it out

 

[RMc]

http://www.advancedaquarist.com/2013/12/lighting Another, very recent article, on LED vs Sunlight spectrum

 

[BackInTheTank]

I am just saying thank you for this thread. That way I can find it again on my profile faster and when I have the time to read everyone's thoughts on it!!

 

[cilyjr]

http://www.advancedaquarist.com/2013/12/lighting Another, very recent article, on LED vs Sunlight spectrum

It was this article that got me on this discussion to begin with. I was listening to a podcast which referenced it while I was driving north to buy coral from another member. This quote in particular is what I am really wanting to explore here

There are intriguing reports of hobbyists and commercial coral farms growing brilliantly colored corals under extremely low light levels. At present, the hypothesis is that the relatively high amount of blue light at relatively low light intensity (PAR) is the environmental trigger for not only rapid growth but extreme coloration as well. This flies in the face of opinions of many hobbyists, riddle dec2013

I enjoy Dana Riddles articles.

 

[cilyjr]

Another useful article on light spectrum: http://americanaquariumproducts.com/Aquarium_Lighting.html

I found this difficult to read. And it in my opinion made too many statements data that is still open for discussion. In particular when cytokinin is formed as they seem to be different for different chlorophylls.

Here's a read for you all
http://www.mbl.ku.dk/mkuhl/pages/PDF/Kuhl_et_al_1995.pdf

This study is exploring more the relationship of zooxanthellae and coral respiration in light vs darkness. I did find some information that stuck out.

Scalar irradiance reached up to 180% of Eat the coral tissue surface for wavelengths subject to less absorption by the coral tissue (600 to 650 run and >680 nm).The scalar irradiance spectra exhibited bands of chlorophyll a (chla)(675run), chl c (630 to 640 nm) and pendinin (540 nm) absorption and a broad absorption band due to chloro- phyll~and carotenoids between 400 and 550 nm.

Basically saying the coral was more interested in the 400 to 550 nm light. And was reflecting the 600 ish. Further the study goes on to show that absorbed light reflects off the coral skeleton but cannot easily pass back through the water tissue interface. Which leads to higher concentrations of the initially absorbed light.

 

[cilyjr]

Here's the most compelling article I've stumbled on so far

http://www.advancedaquarist.com/2003/11/aafeature

So this is what I found interesting ( for those who don't want to do the reading) The Pocillopora coral tissue bleached ( but did not die) under light from the 660 nm lighting and Coral pigment increased under 450nm lighting the uv light had zero effect on the coral.

It appears that red light induced bleaching in the two experiments. It is also worthy to note that bleaching was noticed on Day 22 and Day 23 of the first and second set of experiments, respectively, even when red LED lamp intensity differed by ~20%. What would explain this? In the 1940's, Emerson et al demonstrated that monochromatic red light (at 680 nm) is about 36% more efficient in the promotion of photosynthesis than monochromatic blue light at 460 nm (reported in Hall and Rao, 1999). This is possibly due to the direct absorption of red wavelengths by chlorophylls and Pigment 680 (P-680) found in specialized chlorophyll molecules within the reaction centers of Photosystem II. The relative inefficiency of monochromatic blue light (as opposed to monochromatic red light) to promote photosynthesis might be caused by the less than perfect transfer of light energy collected by chlorophylls a and c, as well as some accessory antennae pigments- the major accessory carotenoid peridinin has been shown to transfer harvested light energy with >85% efficiency (Schofield et al., 1996). The energy collected by these pigments is channeled to the specialized P-680 chlorophyll molecules, and the convoluted process of photosynthesis is begun. RIddle 2003

Basically saying that red light might be too efficient for the coral to use as it has adapted to life with out it (or very little) and when exposed the coral bleaches possibly due to an excess of potential toxic byproducts from the photosynthetic process.

So again I ask why have so many stated that coral will grow faster under light that is "redder" when most data suggest otherwise?

My thinking is that many people took what we know about photosynthesis from surface dwelling plants and just applied the thinking to symbiotic zooxanthellae.

 

[RMc]

I think the general consensus is that because the blue spectrum is least attenuated by seawater it has become the preferred spectrum for zoox energy production.

Because red light is attenuated significantly more than blue at a depth of 10-30 feet it's not much of a jump to assume that the horsting coral may be more sensitive to ed light. It might not be that the red light is overloading the photosynthetic capabilities of the coral, but that a red light of a high intensity (to an unacclimated coral) may signal or indicate a very high exposure to light in general - at which point some zooxanthellae may be expelled.

Photoreactivity (what causes polyps to open or close in response to light) is stimulated by the lower blue and UV spectrum. Again, if one were not exposing a coral and thus the hosted dynos to the photoreactive wavelengths while simultaneously exposing the coral to high levels of red light it could have unintended consequences unrelated to general photosynthetic response. Sounds like a stressful situation for the coral where it hasn't been adapted to the light source.

Also note that the study says that the change in pigment was due to an increase or decrease in zooxanthellae density rather than pigmentation or chlorophyll levels of the individual algal cells - this indicates that it was expelled in response to the exposure. Wich can also happen in response to temperature, water chemistry, and anything else that can cause stress to the coral.

I think the implications of this study's results are unclear, but it is very interesting nonetheless. My gut tells me that regardless, you're going to need some blue light for photoreactivity and caratene response.

 

[cilyjr]

Because red light is attenuated significantly more than blue at a depth of 10-30 feet it's not much of a jump to assume that the horsting coral may be more sensitive to ed light. It might not be that the red light is overloading the photosynthetic capabilities of the coral, but that a red light of a high intensity (to an unacclimated coral) may signal or indicate a very high exposure to light in general - at which point some zooxanthellae may be expelled.

Possible however in the 2 studies the red light of the same wavelength was at different intensities with the 2nd being 20% less and bleaching still occurred at roughly the same exposure time. Also correct me if I am wrong but aren't wavelengths at the lower end considered to have more radiant energy? Isn't that why red is filtered out so easily as it enters the more dense water as opposed to traveling through air?
Also I believe the lights were placed so that coral was receiving the same intensity of red and blue?

Photoreactivity (what causes polyps to open or close in response to light) is stimulated by the lower blue and UV spectrum. Again, if one were not exposing a coral and thus the hosted dynos to the photoreactive wavelengths while simultaneously exposing the coral to high levels of red light it could have unintended consequences unrelated to general photosynthetic response. Sounds like a stressful situation for the coral where it hasn't been adapted to the light source.

So I am not following you here. The closing and opening of coral polyps seem to me to be a moot point especially considering wild specimens are largely closed in the day yet photosynthesis is occurring.

I see your point. Could some red perhaps have some benefits if first exposed to the blue. This is the best argue meant I have heard as yet!

Also note that the study says that the change in pigment was due to an increase or decrease in zooxanthellae density rather than pigmentation or chlorophyll levels of the individual algal cells - this indicates that it was expelled in response to the exposure. Wich can also happen in response to temperature, water chemistry, and anything else that can cause stress to the coral.

Correct. in this case exposure to a 680 nm wavelength. For the purpose of my argument it does not matter weather bleaching occurred do to algeal depletion or a response from the chlorophyll only that the host organism is not receiving the conditions for optimal growth.

I think the implications of this study's results are unclear, but it is very interesting nonetheless. My gut tells me that regardless, you're going to need some blue light for photoreactivity and caratene response.

I agree this study is not the period on the discussion. As far as blue light this is what I am driving at. I more question the need for any red in the spectrum at all. Meaning why would one even think of using a bulb with a kelvin rating of less than 14k?