Corals bleaching? High N&P/Low N&P > imbalanced N&P

[BigJohnny]

Also high phosphate/low nitrate > low phosphate/high nitrate, according to this study. Dont go chasing numbers as this was just one sample of euphyllia, but an interesting read none the less. We need more of these types of experiments for our hobby!

Phosphate deficiency promotes coral bleaching and is reflected by the ultrastructure of symbiotic dinoflagellates
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5441187/

 

[Randy Holmes-Farley]

Thanks for the link!

So folks understand, here's what they mean by high and low:

high nitrogen/low phosphorus (HN/LP = ~ 38 μM NO3−/~0.18 μM PO4−; N : P ratio = 211:1)
That means
phosphate: 0.017 ppm
nitrate: 2.4 ppm


and low nitrogen/high phosphorus (LN/HP = ~ 0.06 μM NO3−/~3.6 μM PO4−; N : P ratio = 1: 60)
That means
phosphate: 0.34 ppm
nitrate: 0.004 ppm

From the paper:

"Corals exposed to the imbalanced, HN/LP conditions, displayed a smaller polyp size and a bleached appearance that closely resembled the phenotype observed in low nutrient water (LN/LP)"

So that means phosphate: 0.017 ppm , nitrate: 2.4 ppm was suboptimal.

"In contrast, the corals kept under LN/HP imbalanced nutrient levels showed a similar phenotype to the nutrient replete (HN/HP) treatment. "
That means that phosphate: 0.34 ppm, nitrate: 0.004 ppm seemed adequate for polyp extension, but had effects on zoox

Final conclusion:

"Our study suggests that phosphate can become critically limiting even at concentrations ≤ 0.18 μM if the N : P ratios well exceed 22:1. This appears surprising since phosphate concentrations in this range are commonly considered ambient or high in natural reef environments. However, Lapointe (1997) reports phosphate concentrations of 0.1–0.18 μM at N : P ratios in the range of 33–72 to be associated with phosphate limitation of macroalgae in the declining reefs of Discovery Bay (Jamaica). These data suggest that the critical threshold values determined by our laboratory study can indeed be found in reef environments impacted by eutrophication. "

 

[BigJohnny]

Thanks randy, I messed up the title lol. High N & High P/Low N & High P > Low N & Low P/High N & Low P

 

[BigJohnny]

This quote was interesting to me and just one possible explanation as to why tanks with very high phosphate can still flourish:

"These results, together with the high Fv/Fm values of zooxanthellae from LN/HP corals suggest that the N-limitation sustains a slower but chemically balanced growth while maintaining a functional photosynthesis."

 

[BigJohnny]

The main reason I posted it though is I am sure many people believe corals are more prone to bleaching at low n/low p but not necessarily under the high n, low p condition, which is actually one that many reefers target (2.4ppm, .02 phosphate). In reality they may be better off with >.1ppm phosphate at that nitrate number, which is what I have found to be more ideal in my reef tanks.

Having said that, this is one study on euphyllia, acropora may respond very differently, I don't know. I just like when I find actual experiments about coral and I figured people would enjoy reading it.

What's your take randy? Anything surprise you?

 

[Randy Holmes-Farley]

I'm not sure how to interpret it.

I'd also caution that their system is believed by them to have very little ammonia. Do ours? Not sure.

Their system also lacks organic foods/bacteria that may not be the case in reef tanks.

 

[BigJohnny]

I'm not sure how to interpret it.

I'd also caution that their system is believed by them to have very little ammonia. Do ours? Not sure.

Their system also lacks organic foods/bacteria that may not be the case in reef tanks.

Yea, makes sense. I also believe that corals in a reef tank with a healthy sized fish population and say 4ppm nitrate/.15 phosphate, grow and color up better than the same tank with half the fish but the same 4ppm nitrate/.15 phosphate achieved by over feeding or dosing.

 

[Cnidoblast]

4ppm nitrate is what I would call the golden number for a lps and softie mixed system
I have seen horror stories of high end zoa's and mushrooms dying because of zero nitrate