Coral reefs in Western Indian Ocean at high risk of collapse within 50 years, says new study

A new assessment of the coral reefs of the Western Indian Ocean shows that they are all at high risk of collapse within the next five decades. Ocean warming and overfishing were identified as the main threats.

In the study, published last December in the journal Nature Sustainability, coral reefs in ten countries in the Western Indian Ocean were split into 11 sub-regions, and assessed using the criteria of the IUCN Red List of Ecosystems, a framework developed by the International Union for Conservation of Nature (IUCN) to assess how close ecosystems are to collapse. 

Reefs in all sub-regions were found to be at high risk of complete ecosystem collapse and irreversible damage.

“We’ve known for some time that coral reefs are in decline, but now we know more precisely to what degree, and why,” said lead author Dr. David Obura, Founding Director at Coastal Oceans Research and Development in the Indian Ocean (CORDIO East Africa) and Chair of the IUCN SSC Corals Specialist Group. 

“This assessment reaffirms the urgency of the interlinked climate and biodiversity crises addressed by COP26 last month in Glasgow, and COP15 in a few months in Kunming. We need to take decisive action to address both global threats to corals from climate change, and local ones, such as overfishing.”

Reefs in island nations in the Western Indian Ocean were found to be under particularly high threat. In four of the sub regions (East and South Madagascar, the Comoros, and Mascarene Islands), reefs were assessed as ‘Critically Endangered’ according to IUCN Red List of Ecosystems criteria, while they were found to be ‘Endangered’ in West and North Madagascar and the Outer Seychelles. 

Rising seawater temperatures as a result of climate change were identified as the greatest threat to coral reefs in these island nations. In the remaining four sub-regions, in North Seychelles, and along the entire mainland East African coast from South Africa to Kenya, reefs were classified as ‘Vulnerable’ to collapse. 

Overfishing, by altering the ecology of reefs and promoting algal takeover, was found to pose the greatest overall threat in continental African countries.

“We detected overfishing of top predators on all the reefs from which we had data,” said Mishal Gudka, Senior Scientist and Program Manager at CORDIO East Africa and a co-author of the study. 

“These results highlight the need to improve local fisheries management to ensure the health of reef systems and secure sustainable fish stocks, which support jobs for a quarter of a million people in the region.”

Much like the IUCN Red List of Threatened Species, which assesses the extinction risk of species, the IUCN Red List of Ecosystems objectively assesses the dangers to our natural world in a standardized way that can be applied to all ecosystems globally.

“This study was designed so that it can be applied to coral reefs around the world, building on the recently published Global Coral Reef Monitoring Network coral reef report” said Dr Radhika Murti, Director of the Centre for Society and Governance at IUCN. 

“If the IUCN Red List of Ecosystems criteria can be applied to all coral reef regions around the world, we will have a clear and consistent picture of the status of these vital ecosystems globally and of the most urgent policy measures decisionmakers need to take.”

The study authors analyzed data ranging as far back as 35 years as well as sea surface temperature projections 50 years into the future. Their study area included the east coast of continental Africa from Kenya to South Africa and east to the island states of Seychelles and Mauritius. In total, it comprised around 5% of the world’s coral reefs. 

The work was led by researchers from CORDIO East Africa and involved contributions from researchers across nine Western Indian Ocean countries and from more than 35 institutions.

Photo credit: iStock/ SHansche

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