IUCN Red List of Ecosystems: Coral Reefs of the Pacific

Mathilde Maslin, Vania Andreoli, Kristina Heidrich, Ben Fitzpatrick, Jack V. Johnson, Johanna Johnson, Sangeeta Mangubhai , Mohsen Kayal, Mehdi Adjeroud, Helen Sykes, Karen Stone, Lucy Southworth, Sheila McKenna, Tom Heintz, Sandrine Job, Laurent Wantiez, Mishal Gudka, Franz Smith

Coral reefs of the Pacific region extend across approximately 30°N to 30°S, covering roughly 35 500 km2. They range from tropical waters of Papua New Guinea in the West to subtropical latitudes, such as Southeastern Pitcairn or Northern Hawaii borders. This encompasses 21 coral reef ecoregions as defined by the Marine Ecoregions Of the World (MEOW) and Marine and Coastal Biodiversity Management in Pacific Island Countries (MACBIO) classifications. The region hosts exceptionally diverse coral and reef fish communities, the latter featuring high levels of endemism in various locations, and is characterised by extensive tropical archipelagos and atolls spanning wide gradients in ocean productivity, human influence, remoteness, geomorphology and climatic conditions. These ecosystems face increasing pressure from ocean warming and marine heatwaves, acidification, extreme weather events, invasive and harmful species outbreaks, overfishing, coastal development and pollution. The IUCN Red List of Ecosystems assessment, based on the benthic and fish datasets from the Global Coral Reef Monitoring Network (1993-2024) and the NOAA Degree Heating Weeks (DHW) dataset (1985-2025), found that coral reefs within all 21 Pacific ecoregions were at a high risk of collapse (i.e. featuring declining attributes to levels where the ecosystem transforms into a different type or is completely lost). This result was, however, largely driven by future climate change projections. Indeed, several criteria assessed in this work are still showing optimistic trends at the regional scale, especially when looking at the actual distribution of Pacific coral reefs or when comparing past and recent estimates of coral cover decline. Under Criterion A (decline in hard coral cover distribution), about 72% of the Pacific reef surface area (14 ecoregions) was classified as Least Concern, while 14% (3 ecoregions) was Vulnerable and 13% (4 ecoregions) was Endangered. Under Criterion B (restricted distribution), about 95% of the Pacific reef area (17 ecoregions) was Least Concern, while 3% (encompassing 3 ecoregions) was Vulnerable. Under Criterion C1 (observed thermal stress), the trend is reversed, with 49% of the reef area (9 ecoregions) classified as Vulnerable, 19% (6 ecoregions) as Endangered and the remaining 32% as either Near Threatened (5 ecoregions) or Least Concern (New Caledonia only). Criterion C2 (projected thermal stress) drives the entire Pacific reef area and all 21 ecoregions to Critically Endangered. Under Criterion D (alteration of biotic interactions), about 52% of the reef area (7 ecoregions) was either Least Concern or Near Threatened, 16% (7 ecoregions) was Vulnerable and 32% (7 ecoregions) was either Endangered or Critically Endangered. These results highlight the need to consolidate reef resilience towards future climate change and to reinforce the conservation of coral reef habitats through strengthened area-based management, sustainable fisheries operation, climate adaptation measures and accelerated global efforts to reduce greenhouse gas emissions.