Why Too Much Light Can Be Harmful to Zooxanthellae

[Dana Riddle]

I get private messages about many subjects. This was my response to one such PM:

Too Much Light!

This brief article will present results of an experiment in which a coral was exposed to high intensity artificial light within a setting likely replicated by many reef aquaria. It will also discuss concepts well-established within the world of botanical research -those of the intimate and...

reefs.com

 

[Ron Reefman]

Dana, thanks for the info. But lets suppose I have a hard time with all the scientific lingo in the article. I simple layman terms, in general, at what kind of PAR level are we pushing zooxanthellae too hard. I recognize that different corals will be different levels, but if you had to pick a big, broad, general rule, what PAR at the coral surface is getting to be too much? Maybe even pick 3 levels of PAR for soft corals, lps and sps?

Help us not be part of the masses who are going over the cliff!

 

[Dana Riddle]

Dana, thanks for the info. But lets suppose I have a hard time with all the scientific lingo in the article. I simple layman terms, in general, at what kind of PAR level are we pushing zooxanthellae too hard. I recognize that different corals will be different levels, but if you had to pick a big, broad, general rule, what PAR at the coral surface is getting to be too much? Maybe even pick 3 levels of PAR for soft corals, lps and sps?

Help us not be part of the masses who are going over the cliff!

Thanks for your time reading the article. Since there are at least 200 zooxanthellae species/clades, it is difficult to make generalizations. But that won't stop me. LOL. Simply put, types of zoox are like plants - there are 'sun' types that prefer high light intensity, there are those that prefer 'shade', and there are the 'weedy' types that are highly adaptable. If you're looking at those corals that prefer lagoons, where water tends to be more turbid that oceanic waters, try to give them at least 100 PAR (these corals tend to be fleshy and could not withstand high energy environments such as reef crests.) For SPS corals, maintain PAR of 200 or so (although the minimum amount of light is low, branching corals can self-shade and could lead to problems long term.) If coloration is desired, expression of some colorful proteins increases with light intensity hence PAR of 800 or so is OK (but this opens up another can of worms since there are perhaps 200 colorful proteins described.)

 

[User1]

Thanks for your time reading the article. Since there are at least 200 zooxanthellae species/clades, it is difficult to make generalizations. But that won't stop me. LOL. Simply put, types of zoox are like plants - there are 'sun' types that prefer high light intensity, there are those that prefer 'shade', and there are the 'weedy' types that are highly adaptable. If you're looking at those corals that prefer lagoons, where water tends to be more turbid that oceanic waters, try to give them at least 100 PAR (these corals tend to be fleshy and could not withstand high energy environments such as reef crests.) For SPS corals, maintain PAR of 200 or so (although the minimum amount of light is low, branching corals can self-shade and could lead to problems long term.) If coloration is desired, expression of some colorful proteins increases with light intensity hence PAR of 800 or so is OK (but this opens up another can of worms since there are perhaps 200 colorful proteins described.)

You know you sort of hit a home run with the whole plants like sun, full light, shad, etc. With that comes those pretty helpful tags that are stuck in the soil that even explain what that means. Which then leads me to something this hobby should strongly consider.

Add a similar coral tag below the online photo, wyswyg, or store front.

I know a lot of online retail try but at the end of the day it is so hidden, overlooked, or misrepresented to include vauge it isn't funny. Probably go a long way.

Again - love the sun light correlation. Well said and it actually makes sense when you look at it that way and its relationsip to reef type. Lagoon, crest, or other which make setting up something like a mixed reef all the more challenging because of this.

 

[Dana Riddle]

You know you sort of hit a home run with the whole plants like sun, full light, shad, etc. With that comes those pretty helpful tags that are stuck in the soil that even explain what that means. Which then leads me to something this hobby should strongly consider.

Add a similar coral tag below the online photo, wyswyg, or store front.

I know a lot of online retail try but at the end of the day it is so hidden, overlooked, or misrepresented to include vauge it isn't funny. Probably go a long way.

Again - love the sun light correlation. Well said and it actually makes sense when you look at it that way and its relationsip to reef type. Lagoon, crest, or other which make setting up something like a mixed reef all the more challenging because of this.

Reef tanks are the most difficult saltwater aquaria to maintain, mixed reefs even more so since light and water velocities have to be a compromise. There are a few vendors that list a wyswyg coral's light environment. I suspect the reason many don't is that it's a proprietary secret, one kept close to the vest in a highly competitive market. Of course, if light intensity varies over the course of the photoperiod, DLI would be best report.

 

[Homebrewer]

I get private messages about many subjects. This was my response to one such PM:

Too Much Light!

This brief article will present results of an experiment in which a coral was exposed to high intensity artificial light within a setting likely replicated by many reef aquaria. It will also discuss concepts well-established within the world of botanical research -those of the intimate and...

reefs.com

Thanks for this paper. I read scientific articles on a regular basis, but not in this field, so pardon the following question...

The utilization of the very short photo period, was that just for experimental purposes or do the results regarding intensity also have implications as it relates to saturation over time? I suppose what I mean is that if a coral is hit with super-high intensity light for a very short time, vs lower PAR over a longer period of time, what are the implications?

I guess I was thrown a bit from the sample coral that was collected in an area that may reach up to 1,000 PAR, and probably lived in an area with at least a 10 hour photo period.

Again, sorry if I missed it in the article. Likewise, if you have another paper that covers that question, kindly send that along if you could!

Very much appreciate your knowledge.

 

[Dana Riddle]

Thanks for this paper. I read scientific articles on a regular basis, but not in this field, so pardon the following question...

The utilization of the very short photo period, was that just for experimental purposes or do the results regarding intensity also have implications as it relates to saturation over time? I suppose what I mean is that if a coral is hit with super-high intensity light for a very short time, vs lower PAR over a longer period of time, what are the implications?

I guess I was thrown a bit from the sample coral that was collected in an area that may reach up to 1,000 PAR, and probably lived in an area with at least a 10 hour photo period.

Again, sorry if I missed it in the article. Likewise, if you have another paper that covers that question, kindly send that along if you could!

Very much appreciate your knowledge.

The Montipora was subjected to a maximum PAR of 1,000 in its natural environment, but had been held in an outdoor tank for a few months where maximum PAR was ~800 (of course the photoperiod matched.) The goal of this procedure was to see what happens when a coral adapted to high light is suddenly exposed to high intensity light (in this case a metal halide.) The results show that the coral could not adapt to high light and would do well at much lower light than its experiences at noon in nature. This is evidenced by a collapse of photochemical quenching and then protection offered by the xanthophyll cycle. In short, high intensity shuts down photosynthesis and lower light, as long as it is around the photosaturation point (usually PAR of 300 or so) is preferable since photosysnthesis is driven at a maximum rate.

 

[Homebrewer]

The Montipora was subjected to a maximum PAR of 1,000 in its natural environment, but had been held in an outdoor tank for a few months where maximum PAR was ~800 (of course the photoperiod matched.) The goal of this procedure was to see what happens when a coral adapted to high light is suddenly exposed to high intensity light (in this case a metal halide.) The results show that the coral could not adapt to high light and would do well at much lower light than its experiences at noon in nature. This is evidenced by a collapse of photochemical quenching and then protection offered by the xanthophyll cycle. In short, high intensity shuts down photosynthesis and lower light, as long as it is around the photosaturation point (usually PAR of 300 or so) is preferable since photosysnthesis is driven at a maximum rate.

Ah, thank you. So if I understand correctly, the photoperiod in the experiment was shortened because it didn't need to be any longer than it was. Once the collapse was seen, it was no longer necessary to continue lighting.

To your point about photosaturation, once that is achieved, maintaining that over a prolonged period of time would should allow the coral to continually "eat" via photosynthesis... is that correct? Assuming then an artificial lighting setup allows a given coral to reach the point of photosaturation, is there a point in time at which photochemical quenching would occur and protection would ensue?

In other words, given this information how does one go about programming a lighting schedule that maximizes photosynthesis but minimizes the damage that could occur?

 

[User1]

Reef tanks are the most difficult saltwater aquaria to maintain, mixed reefs even more so since light and water velocities have to be a compromise. There are a few vendors that list a wyswyg coral's light environment. I suspect the reason many don't is that it's a proprietary secret, one kept close to the vest in a highly competitive market. Of course, if light intensity varies over the course of the photoperiod, DLI would be best report.

I agree. So much that I'm pretty much done trying to manage one. Whatever SPS I have for test frags are it. At this point in time I'll let the corals sort it out to see what type becomes the more dominate one and go from there. Flow as been the biggest challenge for me anyway.

Side question. What is DLI?

 

[Dana Riddle]

Ah, thank you. So if I understand correctly, the photoperiod in the experiment was shortened because it didn't need to be any longer than it was. Once the collapse was seen, it was no longer necessary to continue lighting.

To your point about photosaturation, once that is achieved, maintaining that over a prolonged period of time would should allow the coral to continually "eat" via photosynthesis... is that correct? Assuming then an artificial lighting setup allows a given coral to reach the point of photosaturation, is there a point in time at which photochemical quenching would occur and protection would ensue?

In other words, given this information how does one go about programming a lighting schedule that maximizes photosynthesis but minimizes the damage that could occur?

Photochemical quenching in essence means light is efficiently used in photosynthesis, and this occurs when light intensity meets the minimum required by the zoox (the compensation point, where oxygen production meets respiratory requirements( and the maximum required (photosaturation, where an increase of light will not increase the rate of photosynthesis. An analogy would be a car motor at maximum speed and additional fuel will not make the vehicle faster.) Once the photosaturation point is achieved, non-photochemical quenching occurs - this could be the protection offered by the xanthophyll cycle, where light energy is shunted away from Photosystem II, called Dynamic Photoinhibition. If the protective capabilities of xanthophylls are exceeded, Chronic Photoinhibition occurs, leading to damage of the photosynthetic apparatus. If this is minimal, damage is repaired. If Chronic Photoinhibition exceeds a critical state, damage is not repaired and the coral will bleach.
As mentioned, there are 'sun' and 'shade' corals. Montipora capitata is definitely a shade coral, so is Pocillopora molokensis. On the other hand, some Porites corals (or more coreectly) their zoox, are tolerant of light up to about a PAR of 400. Hence, it's a great compromise in an aquarium. Maintaining a PAR value of 100 at the sandbed seems to be about the minimum; higher if SPS corals are at the bottom - 200 seems sufficient. Of course there will be higher light towards the top. Coloration - either through fluorescence, reflection, or acting as anti-oxidants) will help protect corals if light intensity is high. As a footnote, the only photosynthetic animals I've seen that cannot be over-illuminated are Tridacna clams. I could not achieved photosaturation in my experiments, even when using a metal halide lamp. I later found a thesis that confirmed my observation, but the author of that paper had a more intense light source and did not see photosaturation even when PAR approached that of full-strength sunlight (2,000 micromol/m2/sec.)

 

[Dana Riddle]

I agree. So much that I'm pretty much done trying to manage one. Whatever SPS I have for test frags are it. At this point in time I'll let the corals sort it out to see what type becomes the more dominate one and go from there. Flow as been the biggest challenge for me anyway.

Side question. What is DLI?

DLI is 'Daily Light Integral'. The best analogy is this - PAR is reported as Photosynthetic Photon Flux Density (PPFD) in micromol/m2/sec. If this were rainfall, it would be rain drops per square meter per second. Have you ever heard a weather report stating drops per second? Of course not, we're interested in the *total rainfall* (usually inches per event) and that's what DLI is. It reports the total number of photons in the photoperiod (and reported as mol/m2/photoperiod.) I measured DLIs in Hawaii and saw it could be as high as 30 mol/m2/photoperiod. The DLI in my reef is 7.

 

[oreo54]

A a

Side question. What is DLI?

Plug in your static "PAR" number.
Gets more confusing w/ ramping..

Daily Light Integral (DLI) Calculator | Waveform Lighting

With a PPFD input value and total hours of use per day, Daily Light Integral (DLI) values can be calculated using our online calculator.

www.waveformlighting.com

300 PAR over 10 hours.. is a DLI = 10.80
Same as 600 "PAR" over 5 hours.

DLI is usually calculated by measuring the photosynthetic photon flux density (PPFD) in μmol·m−2·s−1 (number of photons in the PAR range received in a square meter per second) as it changes throughout the day, and then using that to calculate total estimated number of photons in the PAR range received over a 24-hour period for a specific area. In other words, DLI describes the sum of the per second PPFD measurements during a 24-hour period.[3]

700 "PAR" and 12 hours of duration = Hawaii...........

 

[Dana Riddle]

Here's an article I wrote about DLI. Disregard the rest of the article.

A Different Look at Lighting: Effects of Prolonged Photoperiod, Spectral Quality, and Light Dosage

Some reef aquaria 'experts' have suggested that we understand all we need to know about lighting of reef aquaria. This article will suggest otherwise.

reefs.com

 

[Homebrewer]

Photochemical quenching in essence means light is efficiently used in photosynthesis, and this occurs when light intensity meets the minimum required by the zoox (the compensation point, where oxygen production meets respiratory requirements( and the maximum required (photosaturation, where an increase of light will not increase the rate of photosynthesis. An analogy would be a car motor at maximum speed and additional fuel will not make the vehicle faster.) Once the photosaturation point is achieved, non-photochemical quenching occurs - this could be the protection offered by the xanthophyll cycle, where light energy is shunted away from Photosystem II, called Dynamic Photoinhibition. If the protective capabilities of xanthophylls are exceeded, Chronic Photoinhibition occurs, leading to damage of the photosynthetic apparatus. If this is minimal, damage is repaired. If Chronic Photoinhibition exceeds a critical state, damage is not repaired and the coral will bleach.
As mentioned, there are 'sun' and 'shade' corals. Montipora capitata is definitely a shade coral, so is Pocillopora molokensis. On the other hand, some Porites corals (or more coreectly) their zoox, are tolerant of light up to about a PAR of 400. Hence, it's a great compromise in an aquarium. Maintaining a PAR value of 100 at the sandbed seems to be about the minimum; higher if SPS corals are at the bottom - 200 seems sufficient. Of course there will be higher light towards the top. Coloration - either through fluorescence, reflection, or acting as anti-oxidants) will help protect corals if light intensity is high. As a footnote, the only photosynthetic animals I've seen that cannot be over-illuminated are Tridacna clams. I could not achieved photosaturation in my experiments, even when using a metal halide lamp. I later found a thesis that confirmed my observation, but the author of that paper had a more intense light source and did not see photosaturation even when PAR approached that of full-strength sunlight (2,000 micromol/m2/sec.)

A a


Plug in your static "PAR" number.
Gets more confusing w/ ramping..

Daily Light Integral (DLI) Calculator | Waveform Lighting

With a PPFD input value and total hours of use per day, Daily Light Integral (DLI) values can be calculated using our online calculator.

www.waveformlighting.com

300 PAR over 10 hours.. is a DLI = 10.80
Same as 600 "PAR" over 5 hours.



700 "PAR" and 12 hours of duration = Hawaii...........

Thanks again. So given the info in these two posts, if my light setup puts out 100 PAR on the sandbed, and the coral is the type that thrives in that environment... provided it is not over-illuminated (i.e., 100 is at or below the quench point)... it stands to reason that growth through increased energy production would increase as the photo period increases (i.e. DLI). That seems obviously logical, but the above would also mean that a coral in that situation would not be damaged simply by increasing photo period, again provided that it is at the right PAR level to begin with.

Do I have that right?

 

[Dana Riddle]

A a


Plug in your static "PAR" number.
Gets more confusing w/ ramping..

Daily Light Integral (DLI) Calculator | Waveform Lighting

With a PPFD input value and total hours of use per day, Daily Light Integral (DLI) values can be calculated using our online calculator.

www.waveformlighting.com

300 PAR over 10 hours.. is a DLI = 10.80
Same as 600 "PAR" over 5 hours.



700 "PAR" and 12 hours of duration = Hawaii...........

I disagree with the 300 PAR and 600 PAR and their respective photoperiods and DLIs. This disregards photoinhibition. If photosynthesis is at photosaturation at 300 PAR and is only 20% at 600, then obviously it is incorrect to make the comparison. Yes, the DLI will be the same, but....

 

[Dana Riddle]

Thanks again. So given the info in these two posts, if my light setup puts out 100 PAR on the sandbed, and the coral is the type that thrives in that environment... provided it is not over-illuminated (i.e., 100 is at or below the quench point)... it stands to reason that growth through increased energy production would increase as the photo period increases (i.e. DLI). That seems obviously logical, but the above would also mean that a coral in that situation would not be damaged simply by increasing photo period, again provided that it is at the right PAR level to begin with.

Do I have that right?

If PAR is below photosaturation then a prolonged photoperiod will be OK. But not a 24-hour cycle - that has been shown to interrupt zoox reproductive cycles. See my comment to Oreo's post.

 

[oreo54]

I disagree with the 300 PAR and 600 PAR and their respective photoperiods and DLIs. This disregards photoinhibition. If photosynthesis is at photosaturation at 300 PAR and is only 20% at 600, then obviously it is incorrect to make the comparison. Yes, the DLI will be the same, but....

Yea I was going to correct that a bit after thinking about it more..
Say 100 PAR for 12 hours or 200 PAR for 6 hours..

Compounding the issue a little is the dynamic nature of sunlight.

how about x = y if one stays under photo-saturation of a chosen organism..

 

[Dana Riddle]

Yea I was going to correct that a bit after thing about it more..
Say 100 PAR for 12 hours or 200 PAR for 6 hours..

Compounding the issue a little is the dynamic nature of sunlight.

how about x = y if one stays under photo-saturation of a chosen organism..

Yup - you got it.

 

[oreo54]

Yup - you got it.

My freshwater experience was showing where one is dealing w/ 50 vs 25 PAR..

 

[Homebrewer]

If PAR is below photosaturation then a prolonged photoperiod will be OK. But not a 24-hour cycle - that has been shown to interrupt zoox reproductive cycles. See my comment to Oreo's post.

Got it. Between this and the other recent posts, totally understand now.

Thank you for helping me wrap my head around this!