This article may cover it (or not, I do not have it):
The symbiotic anthozoan: a physiological chimera between alga and animal. Furla, Paola; Allemand, Denis; Shick, J. Malcolm; Ferrier-Pages, Christine; Richier, Sophie; Plantivaux, Amandine; Merle, Pierre-Laurent; Tambutte, Sylvie. UMR 1112 INRA-UNSA, University of Nice-Sophia Antipolis, Nice, Fr. Integrative and Comparative Biology (2005), 45(4), 595-604. Publisher: Society for Integrative and Comparative Biology.
Abstract
A review. The symbiotic life style involves mutual ecol., physiol., structural, and mol. adaptations between the partners. In the symbiotic assocn. between anthozoans and photosynthetic dinoflagellates (Symbiodinium spp., also called zooxanthellae), the presence of the endosymbiont in the animal cells has constrained the host in several ways. It adopts behaviors that optimize photosynthesis of the zooxanthellae. The animal partner has had to evolve the ability to absorb and conc. dissolved inorg. carbon from seawater to supply the symbiont's photosynthesis. Exposing itself to sunlight to illuminate its symbionts sufficiently also subjects the host to damaging solar UV radiation. Protection against this is provided by biochem. sunscreens, including mycosporine-like amino acids, themselves produced by the symbiont and translocated to the host. Moreover, to protect itself against oxygen produced during algal photosynthesis, the cnidarian host has developed certain antioxidant defenses that are unique among animals. Finally, living in nutrient-poor waters, the animal partner has developed several mechanisms for nitrogen assimilation and conservation such as the ability to absorb inorg. nitrogen, highly unusual for a metazoan. These facts suggest a parallel evolution of symbiotic cnidarians and plants, in which the animal host has adopted characteristics usually assocd. with phototrophic organisms.
I have seen a number of models of nitrate in other organisms, like phytoplankton, but not corals.
Modeling the interactions between ammonium and nitrate uptake in marine phytoplankton. Flynn, Kevin J.; Fasham, Michael J. R.; Hipkin, Charles R. Swansea Algal Research Unit, School of Biological Sciences, University of Wales Swansea, Singleton Park, Swansea, UK. Philosophical Transactions of the Royal Society of London, Series B: Biological Sciences (1997), 352(1361), 1625-1645.
Abstract
An empirically based math. model is presented which can simulate the major features of the interactions between ammonium and nitrate transport and assimilation in phytoplankton. The model (ammonium-nitrate interaction model), which is configured to simulate a generic microalga rather than a specified species, is constructed on simplified biochem. bases. A major requirement for parametrization is that the N:C ratio of the algae must be known and that transport and internal pool sizes need to be expressed per unit of cell C. The model uses the size of an internal pool of an early org. product of N assimilation (glutamine) to regulate rapid responses in ammonium-nitrate interactions. The synthesis of enzymes for the redn. of nitrate through to ammonium is induced by the size of the internal nitrate pool and repressed by the size of the glutamine pool. The assimilation of intracellular ammonium (into glutamine) is considered to be a constitutive process subjected to regulation by the size of the glutamine pool. Longer term responses have been linked to the nutrient history of the cell using the N:C cell quota. N assimilation in darkness is made a function of the amt. of surplus C present and thus only occurs at low values of N:C. The model can simulate both qual. and quant. temporal shifts in the ammonium-nitrate interaction, while inclusion of a derivation of the std. quota model enables a concurrent simulation of cell growth and changes in nutrient status.
Here are some nitrate and coral referecnes:
Nitrate uptake in the scleractinian coral Stylophora pistillata. Grover, Renaud; Maguer, Jean-Francois; Allemand, Denis; Ferrier-Pages, Christine. Centre Scientifique de Monaco, Monaco, Monaco. Limnology and Oceanography (2003), 48(6), 2266-2274. Publisher: American Society of Limnology and Oceanography
Abstract
The authors assessed the uptake rates of nitrate by the scleractinian coral Stylophora pistillata by following 15N from seawater into the coral tissue. Two sets of corals were first prepd., with nitrate-enriched corals grown in 5 mmol/L NO3- and control corals grown in Ã"šÃ‚£1 mmol/L NO3-. Uptake rates at 0.3 and 3 mmol/L [15N]NO3- were then measured. Most of the % 15N enrichment occurred in the zooxanthellae fraction. Uptake rates were not significantly different between nitrate-enriched and control corals, suggesting that they were not dependent on a nitrate acclimation. These rates increased with the in situ nitrate concn. and varied from 1.2 ng/h/cm2 N to 6.1 ng/h/cm2 N in the algal fraction at 0.3 and 3 mmol/L [15N]NO3-, resp. In a second expt., two sets of corals were prepd., with ammonium-enriched corals grown in 5 mmol/L NH4+ and control corals grown in <1 mmol/L NH4+. Uptake rates at 3 mmol/L [15N]NO3- were measured. These rates were significantly lower with high NH4+ concns. in seawater. In the algal fraction, they ranged from 0.1 to 0.6 ng/h/cm2 N in NH4+-enriched corals and from 2.2 to 4.5 ng/h/cm2 N in control corals. Nitrate can therefore be considered as an important source of nitrogen for corals, at least when ammonium concns. are low in seawater.
