Nitrification in Reef Corals

N-Serve blockage of $NH_4^+$ oxidation showed that nitrification in reef corals is quantitatively important. Average $NO_3^-$ production was $9.4\pm6.0 nmol (mg coral tissueN)^-1 h^-1 (mean \pm1 SE; n = 12)$, equivalent to 17% of the $NH_4^+$ consumption and 21% of the uptake by zooxanthellae showing and effective competition for $NH_4^+$ by nitrifiers. $NH_4^+$ utilization rates were equal to inorganic N production rates, and $NO_3^-$ production rates were equal to $NO_3^-$ uptake rates by zooxanthellae, suggesting close coupling between these processes. Density of nitrifying bacteria associated with living corals may vary from $4 to 260 \times 10^3 cells (mg coral tissue $N)^-1$.