Why Too Much Light Can Be Harmful to Zooxanthellae

[JCOLE]

Lots to consider here. Are those light intensities the maximum during the photoperiod? Corals have an arsenal to protect them from excessive light, but only to a point. Reflective or fluorescent proteins can shunt light energy away from photosynthesis. So can xanthophylls and carotenes. With SPS (or any branching/folding coral) self-shading can help to prevent bleaching. I made some observations while in Hawaii of shallow tide pool corals and found areas exposed to 'full-strength' sunlight were bleached (even though they still had a brownish coloration) while shaded areas had high zoox populations. My point is that the human eye is apparently poor at distinguishing bleaching unless it is total. As for stunting growth without bleaching, yes, I think that is possible when light intensity exceeds the photosaturation point but does not rise to chronic photoinhibition.

Yes they are. Full intensity runs from 12:30PM to 8:30PM. See below videos. I just took some PAR measurements. Do you think these are accurate?

Afterwards I made adjustments and now PAR is around 800 at tops and 300 near the sand.

 

[Semisonyx]

Experiments with CO2 injection would be an interesting project as long as the carbonate chemistry isn't really negatively impacted. CO2 passes through biological membranes with relative ease when compared to carbonates, so it would be a juggling act.

I was hoping to also include @Lostreefin original post in your reply to his reply, but the idea intrigues me. I'm wondering if this may be why it seems to me that people who use calcium reactors have overall faster growth?

 

[Lostreefin]

The key would be figuring out how to introduce the CO2 in a way it didn't negatively impact pH. If you close the door of the room with my aquarium with a couple people in there the amount of CO2 increases to the point that my apex alarms because of a pH drop. How could you do it without making the whole tank a calcium reactor?

 

[Semisonyx]

The key would be figuring out how to introduce the CO2 in a way it didn't negatively impact pH. If you close the door of the room with my aquarium with a couple people in there the amount of CO2 increases to the point that my apex alarms because of a pH drop. How could you do it without making the whole tank a calcium reactor?

Most people run their calcium reactors through a kalk stirrer or second reaction chamber to raise the pH.

 

[anth]

This coral calcification study (using Stylophora pistillata) was done using constant intensity lighting (12h on, 12h off):

https://jeb.biologists.org/content/209/17/3413

Main takeaways:

1. Light cycle produced a 2.6 fold calcification increase over dark cycle.

2. Differences in calcification for the 12h light cycle were minimal (near constant calcification rates at a constant light intensity).

Thank you
I would love to hear if anyone who owns an automated testing machine has tried to answer this on a mixed reef.

 

[anth]

The key would be figuring out how to introduce the CO2 in a way it didn't negatively impact pH. If you close the door of the room with my aquarium with a couple people in there the amount of CO2 increases to the point that my apex alarms because of a pH drop. How could you do it without making the whole tank a calcium reactor?

Maybe on a very small tank with a constant auto water change?

 

[Dana Riddle]

Yes they are. Full intensity runs from 12:30PM to 8:30PM. See below videos. I just took some PAR measurements. Do you think these are accurate?

Afterwards I made adjustments and now PAR is around 800 at tops and 300 near the sand.

Goodness. I calculated a DLI for 1500 PAR and 8 hour photoperiod. ~43! The highest I eer saw in a shallow Hawaii tide pool was in the 30s. The DLI in my tank at the sandbed is ~7. As for the Seneye, you can't beat it for the price but it does have some limitations - it's not cosine corrected and holding it by hand can reflect some light into the sensor. But I see you overcame the latter with that wand. Clever.

 

[Dana Riddle]

I was hoping to also include @Lostreefin original post in your reply to his reply, but the idea intrigues me. I'm wondering if this may be why it seems to me that people who use calcium reactors have overall faster growth?

I measure CO2 in my tank using the Hach sodium hydroxide titration method and, before I installed a CO2 scrubber on the skimmer intake, it was averaging about 60 ppm. I've been lazy and haven't checked it since. I recently purchased a atmospheric CO2 meter. It is not a scientific instrument per se, but it does give a general idea. I'll add some CO2 testing to the stack of projects. I need a lab assistant. LOL.

 

[Lostreefin]

I measure CO2 in my tank using the Hach sodium hydroxide titration method and, before I installed a CO2 scrubber on the skimmer intake, it was averaging about 60 ppm. I've been lazy and haven't checked it since. I recently purchased a atmospheric CO2 meter. It is not a scientific instrument per se, but it does give a general idea. I'll add some CO2 testing to the stack of projects. I need a lab assistant. LOL.

Please keep us updated and thanks for being willing to take the time to do experiments to further the hobby and our understanding!

 

[A. grandis]

Goodness. I calculated a DLI for 1500 PAR and 8 hour photoperiod. ~43! The highest I eer saw in a shallow Hawaii tide pool was in the 30s. The DLI in my tank at the sandbed is ~7. As for the Seneye, you can't beat it for the price but it does have some limitations - it's not cosine corrected and holding it by hand can reflect some light into the sensor. But I see you overcame the latter with that wand. Clever.

This is a great thread!
One very important thing to keep in mind when comparing natural sunlight over the ocean and any artificial light over our tanks, among all the other variables including alkalinity, spectrum, temperature, nutrients, etc... is the "ON/OFF switch" found in nature, like the clouds passing by and rainy days. Those give the reef a brake from the sun here and there. Also, summer longer days aren't forever. DIL is the most important subject when planning to lit our tanks IMO. It grabs the info and guide us in regards to PAR. Thank you so much, Dana!!

 

[merereef]

There has been some discussion of the 'zig zag' or 'saw tooth' lighting regimen, but I haven't seen any hard data on it - just anecdotal.

have you noticed running the green or red LED benefits the corals in anyway? If so what effects did you notice?

 

[Dana Riddle]

Excessive red light has been shown to regulate zoox populations/photopigment content. The question is how if even small amounts of red light have a negative impact. As for 'green' light, cyan can be absorbed by the major accessory pigment peridinin. I need to get into the lab!

 

[EMeyer]

This is a great thread!
One very important thing to keep in mind when comparing natural sunlight over the ocean and any artificial light over our tanks, among all the other variables including alkalinity, spectrum, temperature, nutrients, etc... is the "ON/OFF switch" found in nature, like the clouds passing by and rainy days. Those give the reef a brake from the sun here and there.

I've often wondered about this. Anyone have data on the PAR reduction from partially cloudy or stormy weather in natural reefs?

Edit: a quick search reveals some interesting patterns. In a study of variation in natural light levels on reefs at Magnetic Island, Australia (a site I've had the privilege of working at), the authors found that

corals at the site alternate between states of potential light limitation and light stress

, which was primarily driven by variation in turbidity but secondarily by variation in cloud cover.

So this quick search supports what you're saying -- the clear skies PAR that corals experience in nature is not ON all the time, at some sites it appears the light ranges from too high to too low every few weeks. Interesting.

 

[Bpb]

I've often wondered about this. Anyone have data on the PAR reduction from partially cloudy or stormy weather in natural reefs?

Edit: a quick search reveals some interesting patterns. In a study of variation in natural light levels on reefs at Magnetic Island, Australia (a site I've had the privilege of working at), the authors found that
, which was primarily driven by variation in turbidity but secondarily by variation in cloud cover.

So this quick search supports what you're saying -- the clear skies PAR that corals experience in nature is not ON all the time, at some sites it appears the light ranges from too high to too low every few weeks. Interesting.

I have to deduce that a combination of near constant particulate and live food availability, combined with stable environmental chemistry keep the corals healthy and prevent the light stress that would likely cause problems in an aquarium

 

[A. grandis]

Well, I do think heterotrohic (particles, etc) and osmotrophic feeding (dissolved organic compounds, amino acids and vitamins) offers nutrition that is tremendously important to all cnidarians in captivity, but the energy from the autotrophic feeding (light energy) is the most important one. The 3 have their places in the ocean, as we know for so long. In our systems we need to control them very carefully though.
In a closed system we have the lights and organics available by feeding the fish and general metabolism withing the system. By offering particulate and liquid foods we channel that into an optimal nutrition sink, offering the very best to the confined organisms we keep, but only if water quality is in check! I think the simple fact that there are clouds and seasons to provide a resting time in the ocean, adds a special balance to the environment to prevent stress in the long run. I do think that all the ways that the corals get nutrition contributes also to this balance, but in many closed systems we have only the lights and the organics in the water, no particulate feeding, and they still do great! The balance in a closed system is more dependent on quality light with the proper intensity/DLI, and water quality, reaching the balance for that system in particular. DLI is so important! It's what should reflect quality (spectrum), power/peak/resting time (intensity/photoperiod) and uniform distribution to resemble what we find in nature.
I do not believe one type of nutrition can be substituted by another, but because the corals have a huge adaptation ability they will do great with mainly strong quality lights and organics. Occasional particulate feeding can do a lot for the system in the long run, specially for LPS. Every system will have it's own needs. Balance is the key, as we know.

 

[ScottR]

I didn’t read through every post but read the article me. Very interesting. I recall @Dana Riddle doing PAR readings in Hawaii. Cloudy days showed PAR dropping off significantly. We tend to keep our lights at consistent PAR daily. So on natural reefs, they get inconsistent PAR daily. I opted to use the “cloud” function on my LED. I don’t have anything positive to report aside from acros being happy and most importantly NOT DYING I am one to believe that giving SPS a break does benefit the zooxanthellae. Thanks for the research Dana.

 

[EMeyer]

I have to deduce that a combination of near constant particulate and live food availability, combined with stable environmental chemistry keep the corals healthy and prevent the light stress that would likely cause problems in an aquarium

I agree that constant food availability is one of the biggest differences between our tanks and the ocean, and suspect it matters. Nutritional status definitely affects stress tolerance and thats a big difference in nutrition -- feeding constantly in the ocean vs feeding almost never in aquariums.

With that said, most animals in nature experience environmental stress in their normal habitats. I have no reason to think the corals in nature are not stressed by high light. In fact that's one of the theories for the evolution of fluorescent proteins in corals, for use as sunscreen. The simplest explanation seems to be that they are stressed by the high light levels but have adapted to deal with it.

It seems like an important distinction in my mind, because it suggests there may not be a good reason to blast corals with high light in an effort to mimic nature, even recently imported wild acros. (Which is probably good, since none of us are hitting the 1000 PAR I've measured on some shallow Australian reefs )

 

[Nano sapiens]

I agree that constant food availability is one of the biggest differences between our tanks and the ocean, and suspect it matters. Nutritional status definitely affects stress tolerance and thats a big difference in nutrition -- feeding constantly in the ocean vs feeding almost never in aquariums.

While nutrition derived from photosynthesis is undoubtedly very important to photosynthetic corals, as well as feeding on phytoplankton and/or zooplankton, because we can't see them (unless there is a cloudy bloom), I think we tend to underestimate the importance of heterotrophic bacteria and protozoans (free living bacterioplankton and bacteria/archaea attached to particulate matter) to a coral's energy budget. Reef water (natural or aquarium) may look 'clean', but under a microscope it is actually teeming with life:

https://reefs.com/magazine/the-carbon-continuum-heterotrophic-bacterioplankton-and-reef-food-webs/

Coral feeding in this way allows them to obtain the carbon and other nutrients that they need even when not directly fed in aquaria.

With that said, most animals in nature experience environmental stress in their normal habitats. I have no reason to think the corals in nature are not stressed by high light. In fact that's one of the theories for the evolution of fluorescent proteins in corals, for use as sunscreen. The simplest explanation seems to be that they are stressed by the high light levels but have adapted to deal with it.

Not only do they have to deal with excessive intensity/lack of intensity issues, but also altered spectrum from cloud cover, and in certain areas, atmospheric particulates from volcanic eruptions and now human created pollution.

It seems like an important distinction in my mind, because it suggests there may not be a good reason to blast corals with high light in an effort to mimic nature, even recently imported wild acros. (Which is probably good, since none of us are hitting the 1000 PAR I've measured on some shallow Australian reefs )

The way I look at it is this. Since space on the reef is at such a high premium, coral larvae are going to try and settle wherever conditions are 'acceptable'. Acceptable is often not optimal, however, so we find corals in very shallow water under very high light intensity, often higher temperatures than reef typical and even having to endure prolonged periods out of water due to tidal flux (certainly not what any coral would really wish for!). For aquarists to try and mimic such high light intensities has never made any sense to me and thank goodness we have moved on from the 'More light the better' paradigm prevalent a decade or two back.

 

[Dana Riddle]

I agree that constant food availability is one of the biggest differences between our tanks and the ocean, and suspect it matters. Nutritional status definitely affects stress tolerance and thats a big difference in nutrition -- feeding constantly in the ocean vs feeding almost never in aquariums.

With that said, most animals in nature experience environmental stress in their normal habitats. I have no reason to think the corals in nature are not stressed by high light. In fact that's one of the theories for the evolution of fluorescent proteins in corals, for use as sunscreen. The simplest explanation seems to be that they are stressed by the high light levels but have adapted to deal with it.

It seems like an important distinction in my mind, because it suggests there may not be a good reason to blast corals with high light in an effort to mimic nature, even recently imported wild acros. (Which is probably good, since none of us are hitting the 1000 PAR I've measured on some shallow Australian reefs )

It is entirely possible to achieve PPFD of 1000 micromol/m2/sec in aquaria, though this value is usually seen at depths of 6 inches or less. I've seen Acropora colonies growing into these intense light fields, although the exposed branches are often strongly fluorescent or reflective and have low chlorophyll content. The shaded branches - those not photoinhibited - have high chlorophyll content.

 

[Dana Riddle]

Here's an article demonstrating light intensities at depths on sunny and cloudy days.

Imitating Natural Light Quality, Intensity, and Dosage in a Reef Aquarium – Do We Really Want To?

When it comes to reef aquariums, Mother Nature has always been the de facto benchmark aquarists aspire towards. Dana investigates in great detail the quality and quantity of light over natural reefs in order to lay the groundwork to answer the age-old question: what is the best light for...

reefs.com