Phopate and Coraline Algae

[jaefei]

Dear Randy,

how many percent phospate can inhibit calcification in coraline algae growth ?

Your sincerely
JEffry

[Randy Holmes-Farley]

I do not know about coralline specifically, but calcification of certain corals is clearly inhibited by less than 0.2 ppm, and likely much less. I expect that coralline algae may be similar. I'd try to keep phosphate below 0.03 ppm.

I discuss that issue in this article:

The Chemical & Biochemical Mechanisms of Calcification in Corals
http://www.advancedaquarist.com/issues/apr2002/chem.htm

from it:

"Another important issue has to do with the inhibition of calcification by phosphate and phosphate-containing organics. Phosphate is known to inhibit the precipitation of calcium carbonate from seawater. Phosphate also decreases calcification in corals, such as Pocillopora damicornis and entire patch reefs. This inhibition is likely related to the presence of phosphate in the ECF and on the growing crystal surface. Exactly how the phosphate gets in isn’t well understood. Nevertheless, the next time you are worried about phosphate levels in your tank, you can think of calcification inhibition in the ECF in addition to the driving of unwanted algae in your tank.

This inhibition of calcification takes place at concentrations frequently attained in reef tanks, and may begin at levels below those detectable by hobby test kits. For example, one research group found that long term enrichment of phosphate (2 um; 0.19 ppm; maintained for 3 hours per day) on a natural patch reef on the Great Barrier Reef inhibited overall coral calcification by 43%. A second team found effects in several Acropora species at similar concentrations.

Organic phosphate and phosphonate inhibitors of calcification have also been studied and probably work by a similar mechanism. HEBP, a bisphosphonate that is shown below, causes a 36% inhibition of calcification in Stylophora pistillata at 10 um, and stops it completely (99%) at 500 um."

[jaefei]

does nitrate inhibit too ? or just for healthy of the coral ?

[Randy Holmes-Farley]

Nitrate does not inhibit calcification directrly, but it can drive the too rapid growth of the zoox, decreasing calcification that way:

Nitrate Issues
http://www.advancedaquarist.com/issues/august2003/chem.htm

from that article:

"Effects of Elevated Nitrate in Aquaria

In addition to the concerns described above relating to the growth of potentially undesirable organisms that may be promoted by elevated nitrate (especially algae and dinoflagellates), corals can be impacted by nitrate. Many corals may not be bothered by elevated nitrate, or may even grow more rapidly with the readily available nitrogen. But in certain corals, especially those that calcify, there may be negative effects from elevated nitrate.

In most cases where nitrate levels have been examined in relation to the growth of calcerous corals, the effects have been reasonably small, but significant. Elevated nitrate has been shown to reduce the growth of Porites compressa (at less than 0.3-0.6 ppm nitrate),16,17 but the effect is eliminated if the alkalinity is elevated as well (to 4.5 meq/L). One explanation is that the elevated nitrate drives the growth of the zooxanthellae to such an extent that it actually competes with the host for inorganic carbon (used in photosynthesis and skeletal deposition). When the alkalinity is elevated, this competition no longer deprives the host of needed carbon.17

A second study on Porites porites and Montastrea annularis tends to support this hypothesis. They showed that elevated nitrate caused an increase in photosynthesis, in the density of zooxanthellae, and in their chlorophyll a and c2, and total protein, while skeletal growth decreased considerably.18 This effect may not be generally true, however, since elevated nitrate does not appear to have decreased calcification in Acropora cervicornis (though the experiments were carried out under very different conditions).19

One very recent study 20 on Porites cylindrica has reported that elevated nitrate (0.9 ppm) did not increase the rate of photosynthesis or zooxanthellae density, but actually decreased it, contrary to the previous literature. They do not provide an explanation of why their results were different, though they indicated that the corals may have been expelling zooxanthellae, which would confound some of the results. Additionally, all of the corals in the study were stressed in that they lost significant biomass during the study compared to when first collected in the wild. Because of that effect, I do not put much faith in how this study may relate to aquaria where corals are growing rapidly. "

[jaefei]

thanks you very much randy...

[Randy Holmes-Farley]

You're welcome.

Happy Reefing. :)