Nearly every shallow-water coral reef ecosystem in the world faces an extremely high risk of collapse by 2075, the International Union for Conservation of Nature (IUCN) said on 22 October, releasing the first global assessment of coral reefs under its Red List of Ecosystems.
The assessment rated 122 of the 127 tropical and subtropical reef ecoregions it covered, or 96 percent, as Critically Endangered, the highest level of threat. Together they account for 99.8 percent of the 188,362 square kilometres of reef assessed.
The IUCN stressed that Critically Endangered does not mean collapsed. Most reefs still have living coral and still function as reef ecosystems, and the organisation said they can recover if action is taken now.
What collapse means
According to the IUCN, a reef ecosystem collapses when the hard corals that build its living foundation almost disappear and algae, rubble and sponges take over, leaving an impoverished habitat that can no longer support diverse marine life.
One ecoregion, the Western Galápagos Islands, is already classified as collapsed following the 1982–83 El Niño. Four others did not have enough data for a full assessment.
Heat stress from climate change is the most consistent threat, the IUCN said, with marine heatwaves causing mass bleaching with increasing frequency. The 96 percent figure includes projected heat stress under a "middle-of-the-road" IPCC scenario of about 2.7°C of warming by the end of the century. On observed change over the past 50 years alone, 24 percent of reef ecosystems would be Critically Endangered.
Overfishing of parrotfish and groupers, which keep algae in check and balance the food web, threatens 63 percent of reef ecosystems, the IUCN said. Coastal development, pollution and crown-of-thorns starfish outbreaks also drive reef decline.
"It is not too late to give coral reefs a chance to recover," IUCN Director General Grethel Aguilar said, calling for ambitious emissions cuts and stronger protection and restoration of reefs.
The Maldives
The assessment divides Maldivian reefs into three ecoregions: north, central and south. According to the IUCN's South Asia regional summary, all three are rated Vulnerable on observed change and Critically Endangered once projected ocean warming is included.
The summary notes major regional declines in live hard coral cover during the 1998 and 2016 bleaching events, and lists the central Maldives ecoregion as Vulnerable because of declines in hard coral cover and grouper biomass.
More than 250 experts covering reefs in over 80 countries and territories took part in the assessment, which was coordinated by the IUCN, the University of Melbourne and CORDIO East Africa with regional networks of the Global Coral Reef Monitoring Network.