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. "
