Nitrate uptake in the scleractinian coral Stylophora pistillata
Grover, Renaud, Jean-François Maguer, Denis Allemand, and Christine Ferrier-Pagès
Limnol. Oceanogr., 48(6), 2003, 2266–2274

We 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 prepared, with "nitrate-enriched" corals grown in 5 µmol L^-1 NO₃^- and control corals grown in µmol L^-1 NO₃^-. Uptake rates at 0.3 and 3 µmol L^-1 [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 concentration and varied from 1.2 ± 0.2 ng h^-1 cm^-2 N to 6.1 ± 1.1 ng h^-1 cm^-2 N in the algal fraction at 0.3 and 3 µmol L^-1 [¹⁵N]NO₃^-, respectively. In a second experiment, two sets of corals were prepared, with "ammonium-enriched" corals grown in 5 µmol L^-1 NH₄⁺ and control corals grown in <1 µmol L^-1 NH₄⁺. Uptake rates at 3 µmol L^-1 [¹⁵N]NO₃^- were measured. These rates were significantly lower with high NH₄⁺ concentrations in seawater. In the algal fraction, they ranged from 0.1 to 0.6 ng 14 h^-1 cm^-2 N in NH₄⁺-enriched corals and from 2.2 to 4.5 ng h^-1 cm^-2 N in control corals. Nitrate can therefore be considered as an important source of nitrogen for corals, at least when ammonium concentrations are low in seawater.