IUCN Red List of Ecosystems: Coral Reefs of the Western Indian Ocean
Abstract
Western Indian Ocean (WIO) coral reefs extend across the East African coastline from Somalia to South Africa, and eastward to include the Îles Éparses and island states of Madagascar, the Comoros, Seychelles and Mauritius, and the French territories of Mayotte and Réunion. The total mapped area of photic coral reef ecosystems is approximately 8090 km², representing approximately 4.5 % of the global ecosystem extent, and for this assessment they were grouped into 13 ecoregions representing distinct coral reef types across the WIO. The region hosts 350-400 scleractinian coral species and approximately 2,400 reef fish species (~850 endemic to the Indian Ocean), the second most diverse region after the Coral Triangle. These ecosystems face increasing pressure from marine heatwaves causing mass bleaching, overfishing and destructive fishing, land-based pollution and sedimentation, and unsustainable coastal development and tourism practices. This 2025 IUCN Red List of Ecosystems assessment found that coral reef ecosystems across all evaluated ecoregions of the Western Indian Ocean are at a very high risk of collapse. This is principally due to the severity of climate change induced warming predicted to occur over the next 50 years. Heat stress already places all ecoregions at a high risk having experienced widespread impacts from bleaching in 1998, 2016 and 2024. These impacts, compounded by local stressors such as pollution and overfishing, have led to significant declines in the biotic community in nine ecoregions over the past 50 years. Ten ecoregions, making up 89.7 % of WIO coral reefs, are classified as Endangered or Critically Endangered based on observed declines. The results highlight that countries must urgently act to increase holistic, inclusive and equitable approaches to prevent these precious ecosystems from collapsing. This involves immediate and drastic action on climate change alongside implementing solutions to tackle local threats which will not only offer the best chance for coral reefs to recover after climate-driven disturbances, but also provide wide-ranging ecological, environmental and societal benefits beyond coral reefs.
Related
BibTeX
@misc{gudka2026iucn,
title = {{IUCN Red List of Ecosystems: Coral Reefs of the Western Indian Ocean}},
author = {Mishal Gudka and Abigail Mwalimu and Karin Moejes and Nimrod Ishmael and Diana Karan and Melita Samoilys and David Obura and Said Ahamada and Léo Barret and Lionel Bigot and Bruce Cauvin and Gilberte Gendron and Pagu Julius and Juliet Karisa and Ewout Knoester and Alex H. O’Brien and Sean Porter and Ronan Roche and Franz Smith and Gildas Todinanahary and Julien Wickel and Francisco Zivane},
howpublished = {EcoEvoRxiv},
year = {2026},
month = oct,
doi = {10.32942/x2z69s},
url = {https://ecoevorxiv.org/repository/view/15651/},
note = {CC BY-NC 4.0},
}
RIS
TY - UNPB
TI - IUCN Red List of Ecosystems: Coral Reefs of the Western Indian Ocean
AU - Mishal Gudka
AU - Abigail Mwalimu
AU - Karin Moejes
AU - Nimrod Ishmael
AU - Diana Karan
AU - Melita Samoilys
AU - David Obura
AU - Said Ahamada
AU - Léo Barret
AU - Lionel Bigot
AU - Bruce Cauvin
AU - Gilberte Gendron
AU - Pagu Julius
AU - Juliet Karisa
AU - Ewout Knoester
AU - Alex H. O’Brien
AU - Sean Porter
AU - Ronan Roche
AU - Franz Smith
AU - Gildas Todinanahary
AU - Julien Wickel
AU - Francisco Zivane
PY - 2026
DA - 2026/10/22
PB - EcoEvoRxiv
DO - 10.32942/x2z69s
UR - https://ecoevorxiv.org/repository/view/15651/
AB - Western Indian Ocean (WIO) coral reefs extend across the East African coastline from Somalia to South Africa, and eastward to include the Îles Éparses and island states of Madagascar, the Comoros, Seychelles and Mauritius, and the French territories of Mayotte and Réunion. The total mapped area of photic coral reef ecosystems is approximately 8090 km², representing approximately 4.5 % of the global ecosystem extent, and for this assessment they were grouped into 13 ecoregions representing distinct coral reef types across the WIO. The region hosts 350-400 scleractinian coral species and approximately 2,400 reef fish species (~850 endemic to the Indian Ocean), the second most diverse region after the Coral Triangle. These ecosystems face increasing pressure from marine heatwaves causing mass bleaching, overfishing and destructive fishing, land-based pollution and sedimentation, and unsustainable coastal development and tourism practices. This 2025 IUCN Red List of Ecosystems assessment found that coral reef ecosystems across all evaluated ecoregions of the Western Indian Ocean are at a very high risk of collapse. This is principally due to the severity of climate change induced warming predicted to occur over the next 50 years. Heat stress already places all ecoregions at a high risk having experienced widespread impacts from bleaching in 1998, 2016 and 2024. These impacts, compounded by local stressors such as pollution and overfishing, have led to significant declines in the biotic community in nine ecoregions over the past 50 years. Ten ecoregions, making up 89.7 % of WIO coral reefs, are classified as Endangered or Critically Endangered based on observed declines. The results highlight that countries must urgently act to increase holistic, inclusive and equitable approaches to prevent these precious ecosystems from collapsing. This involves immediate and drastic action on climate change alongside implementing solutions to tackle local threats which will not only offer the best chance for coral reefs to recover after climate-driven disturbances, but also provide wide-ranging ecological, environmental and societal benefits beyond coral reefs.
ER -