Figure 11.

Conceptual model on the biochemical mechanisms involved in the contrasting coral bleaching responses to different sources of dissolved inorganic nitrogen [nitrate (NO₃⁻) and ammonium (NH₄⁺)] under thermal stress. Moderate seawater enrichment with nitrate leads to a transient imbalance in coral’s redox status, while ammonium benefits their energy metabolism. Nitrate enrichment under thermal stress significantly decreases coral’s aerobic scope and increases oxidative stress condition and bleaching response compared to a low-nitrogen condition. Ammonium enrichment under thermal stress maintains the stability of the symbiosis and does not lead corals to an oxidative stress condition.