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Coral Pigments

By Dana Riddle and Andy Amussen. Presented on 04/26/98 on #reefs IRC.

Tropical coral reefs are noted for their spectacular coloration. However, maintaining these colors under captive conditions has proven to be an enigma for many.

Our studies focused on those parameters thought to promote and maintain pigmentation in corals particularly the small-polyped scleractinian (SPS) corals (SPS genera generally include Acropora, Pocillopora, Montipora, Stylophora and others). These experiments were conducted at the Mariculture Research Institute in Cleveland, Tennessee. Many of the light measurements were collected in various aquaria across the USA as well as in our facility.


Light has long thought to be one of the principle factors for inducing coloration. Our studies indicate that there may be coloration thresholds, that is, vivid pigments may be promoted when a minimum amount of light energy is exceeded.

We use Photosynthetically Active Radiation (PAR) as the metric and report light intensities as microEinsteins per square meter per second (µE·m2·sec, or for brevity µE). PAR counts the numbers of photons in the visible light spectrum (400 - 700 nm). As a reference point, the sun at noon in a cloudless sky generally has a PAR value of 2,000 µE.

We found some pigments to be promoted at relatively low PAR values (reds at 200 µE) while others required much more intensity (mauve at 500-600 µE).

Ultraviolet Radiation

Ultraviolet radiation are those wavelengths below visible light. Our studies used a radiometer with probes designed to measure UV-A (max. sensitivity @ 365 nm) and UV-B (max. sensitivity @ 310 nm). The radiometric units are microWatts per square centimeter per second (abbreviated as µW·cm2·sec, or µW). As a reference, temperature latitude UV-A is ~2,000 µW and UV-B is ~ 1,000 µW.

Our facility uses 400 watt metal halide lamps in pendant fixtures. These fixtures (technically luminaires) have acrylic material shields that very efficiently absorb UV radiation.

Typical UV readings taken at the water's surface are 1 µW UV-A and 0.1 µW UV-B. We also checked the acrylic material for its UV transmission properties (using a UV/VIS spectrometer). e found essentially no UV radiation below 395 nm. Therefore, we conclude that UV radiation is not necessary to promote many desirable colors. (We should note that many corals fluoresce under UV-A radiation. Green fluorescence is very common under UV radiation. However, many colors do not fluoresce under similar conditions and, subjectively, the colors seen under UV are less desirable.)


We offered this information and were a bit surprised at the debate these comments generated. This is the background - we have 10 - 1,500 gallon systems in our facility; four of these house stony corals. e allowed the alkalinity to drop in these systems to that of natural seawater (~ 7 dKH). We noted that many of these corals' colors faded during this period.

Two commercially available buffers (Inland Seas and Warner Marine Research) were used to quickly raise alkalinity levels to 10 dKH. In some cases, the pigmentation intensified overnight. Other colors returned over a period of days. No other system parameters were altered. This procedure was performed in two other systems with the same results.

We are not sure why the colors return - is the increased bicarbonate a catalyst for increased photosynthesis? Or is the alkalinity shift a stressor to the corals and they lose (or alter) their zooxanthellae and the pigments (which are below the zooxanthellae "layer") become apparent. Testing is underway to determine the effect of alkalinity on zooxanthellae density/size and, with any luck, photodocumentation will be presented at the September MACNA X in Los Angeles, California.

Water Motion

All aquatic objects are surrounded by a thin layer of stagnant water called the boundary layer. The thickness of the boundary layer is dependent upon water motion. Generally, water movement is associated with a thin boundary layer and vice versa. This concept is very important as the diffusion of trace elements and other substances can be negatively affected by a thickened boundary layer. d other substances can be negatively affected by a thickened boundary layer. This phenomenon may help explain why "adult" coral colonies do not generally adapt very well to captive conditions while much smaller fragments of the same animal would have an increased chance of survival.


Almost as an afterthought, we took genetically identical Acropora fragments and placed them side-by-side in an aquarium. Great care was taken to ensure both animals were kept under almost identical conditions - a metal halide lamp was mounted on a moving(and reversing) "light rail" (this provided equal intensity and spectrum).

Powerheads (small centrifugal pumps) were positioned to provide closely matching water velocities. An acrylic cylinder (with its top above water) isolated one fragment for an hour or so while it was fed rotifers enriched with highly unsaturated fatty acids (HUFAs) and other ingredients including trace elements, spirulina, etc. The other coral was not intentionally fed. After 60 days, no significant coloration differences were noted between the two corals.

Interestingly, growth measurements made before and after the experiment suggested that growth forms were affected. The unfed coral grew wide while the fed coral grew tall. We present this data only as that which we observed; experiments with larger population sizes and greater controls are in the planning stages.


We suggest that lighting, water motion and alkalinity all seem to be important for the maintenance of SPS pigmentation. Serious hobbyists should obtain a submersible light meter as light levels can significantly change over the space of just a few inches (See our website - for PAR/lux conversion factors). We also suggest that hobbyists maintain high alkalinity levels (~10 dKH) in their aquaria.

We caution hobbyists to raise the alkalinity levels slowly over the course of a week or so. Water motion can be easily maintained by using powerheads and we suggest one powerhead rated at 500 gallons per hour (1900 liters per hour) be utilized for every two feet (0.6 meters) of tank length We'll note here that our research efforts continue to determine water velocity requirements for different shape and size coral colonies.

Now it is time for the questions........

Q: To what degree to you feel water motion is a necessity for keeping corals colorful?

Nutrient uptake is directly related to water motion - so its very important. I just received a jourmal paper with this info as well. DR

Q: Your tanks are 1,500 gallons. What do you use for water motion?

Three 10 gallon dump buckets DR

Q: For a pigmentation that requires a low PAR threshold to exhibit, is there any impact (positive or negative) to exceeding that threshold?

Yes, some corals have died with higher PAR values - the trick is to generate colors and keep the power bill under control DR

Q: On pg 100 of "The Captive Reef" there is a P.A.R. chart comparing Fluorescent and MH lights in a 70g tank. If a coral requires (mauve at 500-600 µE) it appears the Fluorescent are much better at achieving it. Is this correct?

Fluorescents are much better at generating fairly even pAR over the length of the tank, much easier to use. DR

Q: Can you reccomend a light meter for the hobbyist that would be faily accurate and reasonable in price?

Plan to spend about $150 US for a light meter - and waterproof it! DR

Q: From the Estimations of PAR chart in The Captive Reef, it appears that Metal Halide lighting has a better "amount of usable light reaching the coral" in deep aquariums - say 36+ inches deep. Do MH work better for deep tanks?

MH's are better simply because they focus the PAR into a tight beam. DR

Q: If UV does not improve coral pigmentation, should all MH lamps be shielded. And if so with what media?

IMO, yes, shield the MH's with Plexiglas OP-3. Dr

Q: do these parameters hold true for Soft coral colors as well as SPS's?

Very good question - we haven't done any work with soft coral pigments and I've never seen any stuides. DR

Q: What could one expect in a tank with water flow as high as 8-9 fps?

The most I've ever measured was 7 feet per second - this amount of velocity would probably shear tissues from the skeletons! DR

Q: How often should the Simple Surge box you designed be surging to maintain healthy corals?

I ran mine every 45 seconds or so - the important thing is just to flush stagnant water from the interstitial spaces. DR

Q: Doesn't a plain window glass do about the same thing as OP-3 at cutting UV?

No - green glass transmits a lot of UV. DR

Q: do you recommend heavy dosing with iodide and trace element formulas?


Q: What kind of surge velocities do you get from a ten gallon dump bucket?

It depends upon the height of the bucket, pipe diameter, etc. but i would guess maybe 4 fps. DR

Q: Can you describe the tank occupants/health for the tank in which you measured 7 fps flow?

The velocity of 7 fps was at the discharge of a 50 gallon surge device that was about 6 ft. above the tank. I would not recomment these velocities. Reefs usually experience 6 centimeters per second. DR

Q: How do you find Power Compacts at keeping color in corals?

PCs have good PAR - higher than VHO's - so PC's do very well in most cases. DR

Q: I've noticed that when 400w 6500K are added to a tank with coralline, the corraline bleaches. What is the proper acclimation procedure to prevent this?

IMO, 400 watt lamps genertate too much PAR for most corallines. Cut back on the light! DR

Q: What specific bulbs do you use? What is your bulb replacement schedule? On what specific ballasts do you operate these bulbs?

400 watt Iwasakis and Coralife Daylights - last about two years - we use the wrong ballast for the Iwasakis - just a standard CWA ballast. DR

Q: Could you elaborate more on the necessity of a uv shield,and doesn't the glass envelope on the metal halide bulbs provide suffient uv protection?

No, the outer envelope transmits a lot of UV. Many animals adjust to the UV - many do not and die. DR

Q: Are you familiar with Extech light meters and can the sensor be waterproofed in such a way as to make it submersible without significantly affecting measurements?

I'm not familiar with that brand name - the scientific houses and some pet mail order places have good meters for about $150. Take the sensor apart and silicone it to waterproof it. DR

Q: Your findings are interesting as I have experienced the exact opposite- Once I removed the plexiglas from my 250W MH (Iwasaki 6500K bulbs) the coloration on my corals increased drastically. Any idea why?

Perhaps the shield reduced the PAR to very low levels. It is PAR that generates color, not UV. DR

Q: Do calcium/CO2 reactors keep alkalinity around 10dKh adequately?

Yes, but maintain them with periodic inspections! DR

Q: Does the same replacement time frame hold true on Iwasaki 250watt with ICECAP ballast?

Good question - I've got the IceCap e-ballasts now and am experimenting with them. DR

Q: Aside from affecting planula settlement, are there any other documented harm from UV?

More than I could ever list here. HIMB has a whole book full. Hawaiian Institute of Marine Biology - DR

Q: If the coral pigmentation/colouring is not effected to any high degree by UV protection pigments, then what is the purpose of the brilliant colouring? Any ideas, i.e. come warning or protecting, or just an evolutionary artifact?

Some of our studies suggest that pigments do reflect PAR - is this really true? Unknown at this time. DR

Q: I've heard VHO bulbs last 6 months - is this true? If so, what happens after that time?

VHO lose ~50% PAR, lux and UV in 5 or 6 months with a standard ballast.DR

Q: What about the dusk to dawn cycle concerning the coloration of corals? Do you have any comments or reccomendations on that aspect of lighting a tank?

I suppose you mean a transition with actinics? Again, low PAR doesn't promote coloration. DR

Q: Where are you on the temperature debate?

Temps of up to ~85 degrees F are OK as long long as the tank can maintain DO levels in an emergency. DR

Q: I've noticed a few of my SPS have lost color, but not all. Could this be a DKH issue as you mentioned, and what is the best way to maintain alkalinity?

Could be dKH - maintain it any way you can - calcium reactor, balanced supplements, etc. DR

Q: Your website lists coral frags for sale with the notation "water-pick". What exactly does that mean?

These are florist tubes for holding roses - "water-Pick" is a brand name. DR

Q: do you plan on doing similar research on pigmentation in soft corals?

Yes, we do. We may present research of this nature at MACNA XI. AA

Q: what is OP3,where whould it be obtained and what is the minimum thickness required for its use as uv shielding?

OP-3 is a type of Plexiglas. Inour studies, thickness did not make significant differences in UV shielding. DR

Q: When you talk about alkalinity, are you talking about carbonate only, or are you including the borate component? Also, do you think this matters much?

Yes, carbonates only. None of the buffers we use contain borates. DR

Q: The Iwasakis last about 2 years without replacement? Doesn't the lamp go through a spectral change which degrades the quality of light before that or does the spectrum remain stable?

Yes - 2 years. There is a shift to the orange end of the spectum. Books say a 20% shift max. DR

Q: How much do Lux meters cost? And do we need a PAR meter?

Decent lux meters - $150 US - use lux-to-Par conversion factors to save $1,000. See our website later this month for these factors. DR

Q: is lexan the same as op-3?

No, they're not the same. Lexan transmits slightly more UV. AA

Q: What is the typical pH range of your SPS systems? Do you use lab-grade probes or general purpose probes? Do you think that the use of one probe has any real advantage over the other?

8.0-8.5; use genral grade (inexpensive) probes - even good ones will last only 6 months. DR

Q: Have you identified whether the coral colour is due to the coral tissue or its symbiotic zooxanthellae or a mixture of both?

The jury's still out on that one. We know that coral chromatophores give corals some of their color, and we know that the zooxanthellae contain chlorophyll A & C, giving a brownish color to the coral. More research happening now. AA

Q: What is the recommended replalcement period for 10000K Metal halides?

6 months -DR

Q: Do you find the style of tank (i.e. glass or acrylic) makes a large difference as to how the true coral pigmentation is viewed?

It could make some difference - but not as much as lighting or other factors. DR

Q: why 6 months for the 10000k and two years for the 6500k?

The halides for blue seem to deteriorate quickly and the lamp makes white light. The 65Ks make much more blue to begin with. DR

Q: when you say the ph probes only last 6 months,does this mean they should be replaced or does recalibration of the meter make them useful again?

Useful life of 6 months - calibrate once a month. DR

Q: Is the sheilding found in a Corallife pendant ok for use or does it need to be supplimented?

Coralife and Hamilton use OP-3. DR

Q: If the replacement on a 6500K is 2 years, for a 10000K is 6 months, the higher the temp, the greater the spectral change over a shorter period?

That would be a good general (but true) statement. DR

Q: What is your oppinion of the 5500K MH bulb?

Generally, good bulbs. Dr

Q: what is your opinion of the 14000K and 20000k bulbs? How often should they be replaced?

I was not impressed with the 14K lamps, 20Ks make good PAR but have a limited life. DR

Q: Any practical suggestions for approximating bulb PAR vs. distance for acclimating from one lighting system to another?

Wow! A book could be written about this -practically, get a lux meter and use the lux-to-PAR factors. If you'll get me some lux numbers, I'll help with the cpomparisons. DR

Thanks for the great talk, Dana & Andy!

Created by liquid
Last modified 2006-11-26 05:21