Zooxanthella Behavior and What it Tells Us About Photoperiods

[Propaganda]

I was reading about photoperiods on the forum last night and came across this thread:

http://www.nano-reef.com/forums/index.php?showtopic=243472

 

Of particular interest was an article scottyreef mentioned from the Journal of Experimental Marine Biology and Ecology, "Motility of zooxanthellae isolated from the Red Sea soft coral Heteroxenia fuscescens" which can be found here:

http://www.sciencedirect.com/science/artic...022098103004180

 

I hit the paywall (as you likely just did if you clicked on the link) and so my reading for the evening was at a close. Fortunately, I work at a university that subscribes to the journal and so was able to download it at work! I was treated to a very interesting paper with some interesting implications about photoperiods in one's reef tank.

 

In particular, there was this very interesting graph. The graph plots motility of the coral's symbiotic photosynthetic microalgae zooxanthellae in relation to the number of hours of lighting. The use of the term motility is a bit difficult here when talking about intracellular endosymbionts, but it is possible* that we can think of this as a measure of the zooxanthellae doing what we want it to do for our corals: Giving the coral the nutrients and energy for life and healthy growth.

 

 

There are five parameters defined on the graph. (1) time to initiation of motility = time between beginning of the light phase and first appearance of motility; (2) lag time = time from onset of the light period to the time taken to achieve half-maximum motility; (3) peak motility time = duration of maximum motility; (4) peak duration = duration of half maximum motility or greater; (5) duration of the motile period = time from initiation to termination of all motility.

 

So how does this all break down? From the time you turn on your lights, it takes about 30 minutes for everything to wake up and to get going. After about an hour and a half after your lights come on, more than half of the zooxanthellae are now active. What follows is about 3 and a half hours of intense zooxanthellae activity, which then falls off rapidly and ends about 8 hours into the light cycle.

 

How might this inform us* about lighting our tanks? I think there are several take-aways worth considering:

 

o You probably don't need to light your tank for more than 8 hours.

By the time the 8 hour mark hits, the party is over and the zooxanthellae's light-induced diel cycle is over. This might* also be why...

 

o You can't make up for low-intensity lighting with a longer photoperiod.

You really only have about a 5 hour window when most of the activity is occurring.

 

o Maybe* an hour of light isn't just an hour of light.

When

the light is being provided matters. Light at the 3 hour mark has a much greater impact than light at the 6 hour mark. This helps explain why someone running an 10 hour day cycle can report the same success as someone running a 6 hour cycle. A 4 hour difference may sound like a lot, but at the end of the cycle, the difference is really pretty minimal.

 

o One should be aware of ambient light.

If your tank is in a room with bright windows, it is probably best to have your lights come on near sunrise. If the ambient light triggers a light-induced diel cycle in low light conditions and your lights come on a few hours later, you will have missed the window in which they can be most effective. I don't know how dark "dark" needs to be, but something worth considering and perhaps something worth more investigation.

 

o This lends support to the concept of multiple, compressed photoperiods.

Most of the zooxanthellae activity happens early in the cycle; 4 hour on, 8 hour off, 4 hour on, 8 hour off photoperiods could well result in more coral growth. (Being mindful of any unintentional ambient light triggers.) And speaking of triggers...

 

o If you need to turn on your lights during the night cycle for some reason, keep it short.

The initialization time in the study averaged about 30 minutes and the researchers limited exposing the zooxanthellae to more than 10 minutes of light during measurements to prevent triggering a light-induced diel cycle.

 

The study also subjected the zooxanthellae to constant darkness. This, not surprisingly, showed no activity at all. More surprising was the fact that zooxanthellae exposed to constant light also showed no activity! Too much light is the same as keeping your corals in a dark closet with the lights out. How long does the dark period need to be? I don't know and have not found any information about that particular question, but will be looking into that some more.

 

Some less interesting/surprising findings from the study were that the diel rhythm could be time shifted or "reversed" (day during night) with no ill effects. All in all interesting stuff! Sorry for the very long post, but I found this study very informative and thought I would share.

 

[*Edit: kgbenson made a very good point below that motility of zooxanthellae might have nothing to do with productive photosynthesis. He may very well be correct. On the other hand, it should also be noted that Miguel Tolosa references this same study in his book Practial Coral Farming as the reason for the rise of coral farms based on the 4 on 8 off light cycle. My intention here is to promote discussion, I am not a marine biologist, nor do I play one on TV.]

Edited May 31, 2012 by Propaganda

[metrokat]

Thanks, great info.

[NanoTopia]

Interesting study, thanks for sharing it.

 

I wonder if starting your light cycle with actinics to simulate sunrise for longer than 1.5 hours would run into the peak motility time. For example, I run my actinics (about 36 watts LED) for 3 hours then my white LED's (about 72 watts LED) come on for 8 hours. Taking into account the study, I would be wasting 1.5 hours of peak motility time with only the actinics on. It would then be more beneficial to only run the actinics for 1.5 hours in the morning then go to the white LED's for 8 hours. Think I'm going to give it a try.

 

 

Also, I wonder about moon lighting, if it were interfering with this motility cycle. Perhaps no moons are better in this case.

Edited May 29, 2012 by NanoTopia

[M&C]

Thanks for putting this together! Interesting read.

[McJosh13]

Wow, very interesting! This could make a huge difference for someone (like me) who has intense light shine in the window at the tank during sunrise for about 30 min while the angle of the sun is low. I will change my photo period to coincide with that time in the morning and see what happens.

[Propaganda]

Also, I wonder about moon lighting, if it were interfering with this motility cycle. Perhaps no moons are better in this case.

 

I tend to think if moon lighting was a huge issue, people would be having more widespread problems because of them. I think most moon lights are in a part of the spectrum that won't trigger a diel cycle. Although particularly bright, broad spectrum moon lights might be problematic. I still intend to run my moon lights, although I am moving my day cycle to coincide with sunrise; my tank sits in a room with two huge 6' x 5' windows, we get a lot of natural light.

[altolamprologus]

Moonlights shouldn't be a problem. Natural moonlight can be quite bright so I would assume corals would have adapted to ignore it. Also, I read an article a while back about the amount of light it takes to trigger photosynthesis. It's actually quite a bit so moonlights and indirect room lighting shouldn't have any affect on the corals.

[NanoTopia]

Okay I'm going to plug the moon lights back in again. Thanks for the info!

[Propaganda]

Moonlights shouldn't be a problem. Natural moonlight can be quite bright so I would assume corals would have adapted to ignore it. Also, I read an article a while back about the amount of light it takes to trigger photosynthesis. It's actually quite a bit so moonlights and indirect room lighting shouldn't have any affect on the corals.

 

I agree about both the moon lights and indirect room lighting. I still think sunlight from windows could be a problem. Morning sun through our windows in the morning can be pretty intense.

[altolamprologus]

I agree about both the moon lights and indirect room lighting. I still think sunlight from windows could be a problem. Morning sun through our windows in the morning can be pretty intense.

Direct sun would definitely start the cycle. Can't you just put up some blinds?

[Propaganda]

Direct sun would definitely start the cycle. Can't you just put up some blinds?

 

I could, but wouldn't want to do so. I live in the middle of a beautiful forest up on a hill, the view is amazing! I'll just start my tank's day when I start mine.

Edited May 29, 2012 by Propaganda

[Propaganda]

Update: How dark is dark?

 

After some more research, I found that photosynthesis requires approximately a minimum of 500-1000 lux. For comparison, a bright office setting is about 400 lux. Now obviously people grow low light plants in office settings frequently, so YMMV. But I thought this info might help in determining how much light might trigger a light-induced diel cycle in zooxanthellae. Reader's digest version: ambient room light should not generally be a concern unless you have an exceptionally well lit room, but use your judgement regarding direct and indirect sunlight. It is hard for us using only our eyes to judge brightness...

 

If I can get my hands on a PAR meter I will post some results from some typical locations.

[Divine]

Nice. I have a bright room. I was wondering about that.. Cool graph.

[FateX9]

very interesting read

thanks for sharing and putting in the work

[icecool217]

Thanks for sharing this information!

Really interesting read.

[cuber14]

So would my split light cycle 4hrs in morning/4hrs at dusk/evening be bad? Tanks in a sun lit room although not direct sunlight and my evening light cycle is mostly for me to view the tank.

[Propaganda]

So would my split light cycle 4hrs in morning/4hrs at dusk/evening be bad? Tanks in a sun lit room although not direct sunlight and my evening light cycle is mostly for me to view the tank.

 

I don't know, this is one of the things I am trying to find out. I also want to run a split cycle for the same reasons you do. That being said, the eight hour dark period at night is certainly a long enough dark period, regardless of what you are doing in the day. I think in the absolute worse case senario, the evening light period just might not be doing as much from a photosynthesis point of view. You may be pouring on less helpful light, but you aren't hurting anything and you can see the tank! In what I personally see as the more likely scenario, the evening light period is actually very helpful given the behavior over time found in the research and you might even get more coral growth than with a single photoperiod.

 

Even our fairly well lit houses are still pretty dark by nature's standards. Everything I have read thus far indicates it requires a good bit of light to trigger a photosynthetic cycle. I'd still like to find out where that threshold lies, however, as this was something I had never considered prior to reading the paper.

Edited May 31, 2012 by Propaganda

[ThePhilosopher]

Thank you for this information. My tank's current photo period is 12 hours, which is way more than necessary from what I can see. I'll slowly start reducing the photo period until it's about 8-9 hours. I'll let you know if this affects growth patterns.

Edited May 31, 2012 by ThePhilosopher

[kgbenson]

The use of the term motility is a bit difficult here when talking about intracellular endosymbionts, but for all practical purposes we can think of this as a measure of the zooxanthellae doing what we want it to do for our corals: Giving the coral the nutrients and energy for life and healthy growth.

 

I am not certain you can make that connection. Just because they only move for a certain period of time (and this may have more to do with migration in the water column of free living zoanthellae than anything else) doesn't mean that they also cease all other activities. The question we would want to know is what happens to photosynthetic activity and is this linked to motility. It may well be that they are only motile for that period of time because once it is over - they are in a well lit area and need not be motile any longer in order to photosynthesize. They may then go on to photosynthesize for hours longer.

 

It is an interesting paper - but it is important not to infer too much from what is presented.

[uglyfish]

I read something about coral's circadian clock that the coral actually anticipates the light cycle and it reacts chemically before the lights turn on (or sun rises). I wonder what that means for the dual 4 hour light periods. The topic is fascinating. Great work on the initial post.

[Propaganda]

I am not certain you can make that connection. Just because they only move for a certain period of time (and this may have more to do with migration in the water column of free living zoanthellae than anything else) doesn't mean that they also cease all other activities. The question we would want to know is what happens to photosynthetic activity and is this linked to motility. It may well be that they are only motile for that period of time because once it is over - they are in a well lit area and need not be motile any longer in order to photosynthesize. They may then go on to photosynthesize for hours longer.

 

It is an interesting paper - but it is important not to infer too much from what is presented.

 

I agree and I very well may be inferring too much. Although I think information like this can drive conversation and experimentation so we can better understand what is going on in a really unique biological system. The study did test zoanthellae in the presence of the primary polyps, so exactly what motility means in that context I'm not sure. My big assumption (and if I didn't make that entirely clear in my post, I apologize) is that the zoanthellae's motility in an endosymbiotic context related to some limiting factor or saturation point for beneficial photosynthesis in respect to the coral. My list of take-aways to consider (not to be taken as any kind of absolute truth) was that making this assumption might help explain some of the behaviors we witness in our tanks, e.g. longer photoperiods can't compensate for lower intensity lighting, people have equal success with seemingly radical shorter photoperiods, etc.

 

I am a mathematician, not a marine biologist. I would really love to have someone who has a more solid understanding of all this to weigh in. If my post seemed too authoritative, it wasn't meant to be, I was just sharing what seemed to be some interesting results. (I have edited my original post to better reflect the assumptions being made.) On the other hand, it should be noted that Miguel Tolosa references this same study in his book Practial Coral Farming as the reason for the rise of coral farms based on the 4 on 8 off light cycle.

Edited May 31, 2012 by Propaganda

[metrokat]

bump for more discussion

[Weetabix7]

Excellent thread and discussion.

I wonder how all of this applies to Macroalgae in our tanks or Refugiums.

[Lingwendil]

I think I may try the 4 on 8 off in my sump once I redo my tank, and see how it affects chaeto and maybe a couple frags.

[danimal1211]

It would be interesting to see how a compressed photoperiod would effect PH stability