Multiple light cycles a day

[MCsaxmaster]

Yup, that's what you typically see. This is measured with PAM fluoremetry and expresses what is going on in the outermost tissues. Inside branching colonies, or in deeper-set tissue in all corals peak photosynthesis occurs during midday because the outer tissues shade the inner tissues. If you integrate over the entire colonies (e.g., by measuring O2 production) you'll see that net photosynthesis for colonies follows light intensity.

Chris

[airinhere]

Is it possible that the photosynthetic variable you are describing might have a major influence in marine tanks? If most scientific studies are focused on mature colonies, but most aquarists have individual frags or immature colonies, could the data being presented be contrary to what aquarists are looking for.

Illustrative example:
Researcher notices that a colony produces more net photosynthesis at times of highest illumination. They also notice a substantial reduction of photosynthesis at these times in parts of the coral that are directly exposed to the source of illumination. Corals that are partially obscured from the illumination are noted to be compensating for this localized reduction.

In an aquarium, almost all the corals kept are part of this direct exposure group. Only in very mature tanks with substantial lighting systems could we see the reduction of photosynthetic activity being compensated for by other members of the same colony. Since most home aquarium corals are in this direct exposure group, perhaps a more detailed look at the mechanics and reactions of the "wild" colonies during the peak illumination should be made.

At what point does the photosynthesis become reduced in these constantly exposed sections of a colony?

What processes are occuring to reduce the photosynthesis?

Are there posssible methods of lighting that could reduce the severity of or eliminate the reduction of photosynthetic activity?

[MCsaxmaster]

Wow, I must say I'm impressed by the shear quality of those questions. I'll respond as soon as I get a chance, but suffice it to say that I do think there are some critically important considerations here both for reef aquarists and for biologists studying the critters. PAM fluoreometry is easy to do nowadays and lots of people do it, but many do it badly without sufficient understanding of the underlying principles and come to conclusions that are, well, bogus.

[reef / aholic]

Originally posted by airinhere
Are there posssible methods of lighting that could reduce the severity of or eliminate the reduction of photosynthetic activity?

Here is something that I found to be interesting within the Photosynthesis and Photoadaptation article by Sanjay Joshi.

Another approach that has been recently developed is the rotating aquarium (Gibbs 1998). Where instead of rotating the lights, the aquarium is rotated along a central axis to the light source.

In fact, on coral reefs this upwelling irradiance may be a significant portion of the total irradiance (Dustan 1982).

So which is more important within a reef system, downwelling light or upwelling light?

[airinhere]

I read that article as well. I think the point about reflected light was that it is unknown how much it assists downdwelling light, but it is just a minor consideration for overall impact of light on corals. They also touched on moving light systems, but pointed out the obvious issue of our tanks only being four or six feet long (on average). In such small areas, the real impact of the light having to go sideways through the water came into question, but is only considered (by the writer) to be of minor influence. Again, the resulting reflected light from the substrate is of even less importance in the moving light system.

Much focus is placed on light system power in wattage and the temperature color of our bulbs. Reflective light, shimmer lines and other supplemental sources of lighting in our tanks can have positive impacts, but I think we are missing the bigger picture.

The Earth spins at a steady pace. Most of our corals come from places where the light from our Sun reach the oceans for about 12 hours daily. There are mitigating factors like weather patterns that reduce the useful light reaching corals in the wild, but it is always based on a 12 hour on, 12 hour off light cycle.

Just because the light system provided by nature is 12 on 12 off, does not mean that corals in our tanks reach peak performance with this type of light schedule.

What if we knew how long certain types of corals could go with intense light reaching them before they began to utilize some sort of light defense mechanism?

Most corals in our tanks are not large colonies. They do not react to light like a large colony would if viewed as a whole. If we are to figure out what is best for our corals we need to stop thinking of a small frag exactly like a mature colony.

By understanding when these light protective mechanisms are used, we can figure out when to reduce our lighting and keep our corals in an enviroment where they can grow without having to devote any energy to other uses like protecting themselves from high light situations.

Our tanks are not "like the ocean". We have unnatural accumulations of organisms,incredibly small amounts of water to work with and linear flow of water (often minimally suited to the life we are trying to keep alive).

Because of the overwhelming amount of obstacles we face to keep our corals alive, I think every advantage should be given to helping keep our corals as healthy as possible.

I feel that my method of dual light cycles has potential as a means of limiting the enviromental stresses on my corals so they can put all their energy into growth. I could be wrong, but if I can find out either way I can alter my system to make it as efficient as possible.

And my corals are doing pretty darn good as it is. I just want to try making things better for them.

[spscrackhead]

i am considering doint this with my tank. i have the tek t5 6 bulb fixture. what amout of time would be best for on and off? should i just turn all bulbs on at the same time or what? what timers are you guys using?

[airinhere]

I am not a scientist nor am I fully qualified to answer any questions of this nature. Any changes you commit to regarding your tank lighting might have unexpected side effects.

Okay, disclaimer aside.

As I understand it, light in nature comes on gradually (as the sun rises) and goes away gradually (sunset). The sunrise or sunset is very short in duration, but the angle of the sun as opposed to the water makes it noon before maximum light intensity is achieved on a reef. So light 'warm up' can take as long as four or more hours. Same thing for the lights dimming.

In our tanks, you turn the light on, and its at full intensity in a few minutes (halide) or instantly (T-5/PC). But still not anywhere near midday light levels on a reef.

My opinion on this is to disregard what is considered "common practice" and turn all the light on and run it at full intensity for five hours (approx). Shut down for 5 hours and then another five hours on at full intensity.

Corals reportedly take about 30 minutes to adjust from dark to light, and I have been using Halide lighting which does take about 5 minutes to come to full intensity. I can only assume that nothing but positive results would be seen by using the 30 minute transition time to gradually bring your lights to full intensity.

Dont sweat turning the lights out gradually. All I can think would occur is just wasting opportunity for maximum light exposure by reducing the light. You only get 12 hours of light with this method (11 hours of useful light).

I have decided on 6 on / 4 off/ 6 on/8 off because this is most convenient for me. 8 am on, 2 pm off.
6pm on, 12 am off.

This also leaves a longer dark period during the actual night. Maybe this can help the corals maintain a circadian rhythym.

Sorry my posts here are so long, but I do not want anyone to just blindly do what I am suggesting, and would rather show my reasoning behind what I am saying. That way if I suggest or advise something idiotic, someone else reading this can chime in and help redirect me.

Again, think out all the impacts this will have on your tank. heating, cooling, pH etc...

[crazzy]

Updates?

[airinhere]

I still am using the dual light cycle. I switched to 10K bulbs with actinic supplementation. Lights were adjusted down an hour for each light cycle when I switched to the new bulbs. So they come on at 8 am and shut down at 1 pm, back on at 7 pm and off at midnight. Two 40W NO actinic bulbs are on from 8 am till midnight.

I still get the lighting requirements of the dual light cycle with a very underpowered actinic effect during the middle of the day. The actinic looks cool, but I dont think its much more useful than just aesthetics.

I switched to 10K lights in the hopes that I will see even more growth in my tanks.

So far, I just hate the color. Increased growth will come in the next few months.

At the very least, nothing has died.

[craab]

I tried 6on, 6off, 6on, 6off with poor results. Did it over a two month period. I have gone back to the more traditional light cycle.