Nutrient Dynamics in Coral Reef Ecosystems

Coral reefs flourish in waters that are often poor in nutrients, hosting an intricate web of interactions between the coral animal, its intracellular algal symbionts and a diverse microbial community. Dissolved inorganic forms of nitrogen and phosphorus are assimilated by symbiotic dinoflagellates and other microbes, transformed into organic compounds and translocated to the coral host. In return, corals release metabolic by-products that support the growth of their symbionts and associated prokaryotes. Nutrient ratios and concentrations govern the balance between mutualistic symbiosis and stress, influencing bleaching susceptibility and growth rates. Ecosystem-scale inputs—from seabird guano to agricultural runoff—further modulate reef productivity, while alterations in fish-mediated nutrient recycling can amend or exacerbate these impacts. Understanding the mechanisms of nutrient uptake, storage and remobilisation is critical for predicting reef resilience in the face of warming seas and anthropogenic eutrophication. This knowledge underlies strategies for catchment-to-reef management, the design of marine protected areas and the maintenance of key biological subsidy sources.

Research from Nature Portfolio

Recent studies have demonstrated that symbiotic dinoflagellates alone can acquire sufficient dissolved inorganic nitrogen and phosphorus to sustain rapid coral growth under laboratory and field conditions, with corals ‘farming’ excess symbionts and digesting cells to access vital nutrients. A natural fertilisation gradient created by seabird colonies confirmed that efficient symbiont nutrient utilisation enhances growth at the ecosystem level. Complementary work has elucidated contrasting roles of nitrogen forms during thermal stress: nitrate enrichment exacerbates oxidative damage and reduces aerobic scope under heat, intensifying bleaching, whereas ammonium enrichment preserves redox balance and energy metabolism, mitigating thermal damage. These findings underline the necessity of managing both nutrient form and source to bolster coral resilience.

Nutrient Dynamics in Coral Reef Ecosystems publication trend

The graph below shows the total number of articles in nutrient dynamics in coral reef ecosystems across all publications each year (not limited to Nature Index journals).

Technical terms

Dissolved inorganic nitrogen (DIN): Inorganic forms of nitrogen such as nitrate and ammonium available for uptake by symbionts and microbes.

Eutrophication: The process by which excess nutrient enrichment stimulates primary production, often leading to ecological imbalance.

Holobiont: The assemblage of a host organism and its associated symbiotic microbes acting as an integrated biological unit.

Photosynthates: Organic carbon compounds produced by photosynthesis that are translocated from algal symbionts to the coral host.

Symbiont farming: The acquisition and controlled digestion of excess symbiont cells by the host to obtain essential nutrients.

References

1. Reef-building corals farm and feed on their photosynthetic symbionts. Nature (2023).
2. Seabirds supply nitrogen to reef-building corals on remote Pacific islets. Scientific Reports (2017).
3. Unravelling the different causes of nitrate and ammonium effects on coral bleaching. Scientific Reports (2020).
4. Meta-organism gene expression reveals that the impact of nitrate enrichment on coral larvae is mediated by their associated Symbiodiniaceae and prokaryotic assemblages. Microbiome (2023).
5. Tracing nitrogen pollution from wastewater on an oceanic, touristic island: Integrating local knowledge and uncertainty into a mass balance modeling approach. Ocean & Coastal Management (2024).
6. Does Trophic Status Enhance or Reduce the Thermal Tolerance of Scleractinian Corals? A Review, Experiment and Conceptual Framework. PLOS ONE (2013).
7. Impacts of nutrient enrichment on coral reefs: new perspectives and implications for coastal management and reef survival. Current Opinion in Environmental Sustainability (2014).