What do criteria A–E mean?
- A
- Reduction in distribution: loss of functioning reef, measured as sites where coral cover fell below 5–10% (A1 past 50 years; A2 projected, next 50 years, Australia only)
- B
- Restricted distribution: very small or few reef areas, with ongoing threats
- C
- Abiotic degradation: more frequent marine heatwaves causing severe bleaching and mortality (C1 past 50 years; C2 projected heat stress, next 50 years, IPCC SSP2-4.5)
- D
- Biotic disruption: balance of corals, algae and fish (coral cover, algae-to-coral ratio, herbivorous and predatory fish)
- E
- Quantitative risk analysis: collapse modelling to 2075 (Great Barrier Reef and Torres Strait only)
The overall risk status is the highest category across all criteria. Collapse = near or complete loss of hard corals (below 5% cover).
More: Full methods (PDF) · Acknowledgements: authors, contributors, data providers and funders (PDF) · IUCN Red List of Ecosystems · RLE Guidelines v2.0 (PDF)
Map data: coral reef extent compiled from UNEP-WCMC, WorldFish Centre, WRI, TNC (2021) Global distribution of coral reefs, v4.1 (www.unep-wcmc.org), Allen Coral Atlas maps (© 2018–2023 Allen Coral Atlas Partnership and Arizona State University, licensed CC BY 4.0) and national or regional reef maps; the layers used in each region are described in the regional reports, together with the reef area per ecoregion (see also Methods, Criterion B). Shown for visualization only, generalized to a ~1 km grid; not for download or redistribution. Ecoregions: IUCN Red List of Ecosystems (2026), based on the Marine Ecoregions of the World (Spalding et al. 2007).
