Résumé
Scleractinian coral evolved under nitrogen (N)-limited conditions. The increase in N flux from anthropogenic activities to these otherwise N-depleted environments is threatening coral health and coral reef ecosystem function. We tested the effect of elevated ammonium (NH4+) loading on Acropora metabolism responses (respiration, gross primary production, and NH4+ uptake) on healthy aquacultured Acropora sp. and compared responses to wild Acropora pulchra from Guam where corals are threatened by eutrophication. We quantified 15N isotope uptake, metabolism in custom metabolism chambers, and tissue N and carbon (C) content following NH4+ loading. For aquacultured Acropora sp., we found that NH4+ loading stimulated primary production and respiration, but did not significantly alter rates of uptake or tissue C or N content. Conversely, the wild A. pulchra did not respond to NH4+ loading and was generally resistant to short-term exposures of NH4+ loading. The change in rates of primary production within the aquacultured coral experiment suggests that sustained increases in N availability could upset stoichiometric regulation in coral. Few studies have coupled N cycling and metabolism rates, so our results serve as an important resource for understanding the biological activity of scleractinian coral, particularly a common wild coral from Guam, where extended events of increased anthropogenic N are increasing disease prevalence and decreasing coral reef diversity.