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Increased Growth of Staghorn Acropora in Higher Phosphate Levels


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I think the important things to note from this study is that the coral density was reduced at a higher phosphate level, which cannot be good for the coral, the study was only done over 4 months, which IMO is not really enough time for slow growers like Acros, and the article brief (full length one might mention this) does not mention coloration at all, which is a big thing for those of us in the hobby.

 

VERY glad to see research like this though.

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  • 4 weeks later...

Another point - high phosphates (higher than used in the article) cause "burning" of the tips in fast growing sps species. It also causes more competitive algae to begin to dominate a system which is never good.

 

From what I've seen, plenty of P is brought in via food if you feed a balanced diet from which most species can benefit.

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I don't know about the phosphates, but high alk has been implicated in SPS tips burning in ULNS (ultra low nutrient systems), aka carbon-dosed systems.

 

High P often associated with browning of a lot of coral species because it feeds the zooxanthellae symbiont in the coral's tissue.

 

Lowered Kelvin (6500K) lighting has also been shown to have positive impact on the growth rate of some corals. Unfortunately, coloration typically suffers. So you can get fast-growing brown corals, or slower growing colorful corals.

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Phosphates interact with the calcium deposition (acretion) - that is why it causes burns when in higher concentrations.

 

As to lower K lights causing brown - I highly disagree. Sunlight is approximately 5500K (filtered to higher with depth of course). If you have a full spectrum 6500k bulb, you will often get far better colors in a wider variety of corals. What causes browning is either low PAR (often from poor output low K bulbs) or variability in light (like you get with higher latitudes using sunlight or irregular schedules). Higher K bulbs reflect those higher colors giving the illusion that you have "brighter" corals in the green and blue range - but its just reflection of the ambient light. Check out Dana Riddle's work on coloration and intensity per spectra.

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I recall the Riddle papers. My recollection could be wrong, but the intensity and spectra that showed strongest response were in the blue and green ranges as I believe. Here's on of the papers. http://www.advancedaquarist.com/2009/1/aafeature1

 

BTW, the brown out may be correlated with zooxanthellae density which tend to be yellow-brown in color and can impede light transmission. I'll have to look around as to where I picked that up. It could be folklore, though.

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You are correct. But thats only for majority pigments. Many pigments absorb in the wider ranges as well - especially blues (from memory, can't remember totally). The key, as he points out in one of those, and I talked to him about this, is that you have to reach saturation state - which occurs for given absorbance for each pigment. Once you hit that state, the corals produce more pigment in order to protect their tissues against the excess light. They stop absorbing at a maxima and start reflecting/blocking that light. His work was with very narrow light spectra, so having definitive results is tough when corals can contain numerous algal-derived pigments.

 

The higher K lights simulate deeper water conditions - which also has many bright corals to be sure - but if you dive many reefs in the Pacific, you will notice that the bright blues and lavender/purples are only present at the surface.

 

From experience in the late 90s when many people first starting using full spectra 6500K bulbs, you can have awesome results. 4500k bulbs were always a flop.

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You know, 6500 was probably bad recollection. I know that Riddle and others got good growth at 6500. Somewhere, I recall his growing stuff (maybe it was a Sinularia) for resale at 6500 and noting that when he displayed it at 14,000K+, he couldn't keep enough in stock because of the striking green that it presented. It's 3500 (the range where most incandescents occupy) that was the problem.

 

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Phosphates interact with the calcium deposition (acretion) - that is why it causes burns when in higher concentrations.

So we know that phosphates interfere with calcification. Why exactly does it burn the tissue?

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I would hazard a guess that what we are calling "burn" is a lack of correct deposition which results in the tissue being unable to continue growing over that area appropriately. I've seen the results once - the tissue almost looks like an RTN attack. Its stringy and flaps around a good bit. Maybe it doesn't attach tightly enough to the skeleton and tears loose?

 

No real idea if anyone has really looked into the issue more closely.

 

There are also likely effects to the growth of beneficial algae associated with the coral, perhaps even shifts in the dominant forms of the dinoflaggelates being hosted too.

Edited by wade
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I would hazard a guess that what we are calling "burn" is a lack of correct deposition which results in the tissue being unable to continue growing over that area appropriately. I've seen the results once - the tissue almost looks like an RTN attack. Its stringy and flaps around a good bit. Maybe it doesn't attach tightly enough to the skeleton and tears loose?

That sounds a lot like the alk burn that people experienced when more ULNS started popping up a few years ago when vodka, vinegar, and sugar dosing started to pick up. You'd get tissue recession on what looked like the axial corallite revealing the bright white skeleton. When people backed the alk down to around 8 dKH, the coral typically recovered. I don't recall anything associating the condition with elevated phosphate levels, though.

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