Corals, Nitrate, and Ammonium

[sculpin01]

I've seen a lot of confusion here regarding coral utilization of nitrate and and ammonium. Corals and zooxanthellae both can import ammonia/ammonium and nitrates. Ammonium/ammonia can be immediately utilized for amino acid synthesis by both the coral cell and the zooxanthella for amino acid synthesis (specifically glutamate). Nitrate cannot be directly utilized for amino acid synthesis by the coral cells but CAN be utilized by the zooxanthellae.

Here's where the magic comes in: the zooxanthellae convert nitrate into ammonium and thereafter into amino acids, which are then FED BACK to the coral cell. So the coral cell definitely does benefit from nitrate, it's just indirectly. The amino acids are thereafter utilized for cell growth via protein synthesis.

Source: The Biology of Coral Reefs (Second Edition); pages 116-119; Sheppard, Davy, Pilling, and Graham; 2019

 

[sculpin01]

This, of course, does not even touch upon coral heterotrophy ("eating prey") or diazotrophy (nitrogen gas fixation) via commensal bacteria:

(PDF) Heterotrophy in Tropical Scleractinian Corals

PDF | The dual character of corals, that they are both auto- and heterotrophs, was recognized early in the twentieth Century. It is generally accepted... | Find, read and cite all the research you need on ResearchGate

www.researchgate.net

Frontiers | Unravelling the Importance of Diazotrophy in Corals – Combined Assessment of Nitrogen Assimilation, Diazotrophic Community and Natural Stable Isotope Signatures

There is an increasing interest in understanding the structure and function of the microbiota associated with marine and terrestrial organisms, because it ca...

www.frontiersin.org