96 Percent of the World's Coral Reef Ecosystems at Extreme Risk, IUCN Warns

The underwater world of colourful corals, countless fish and diverse marine creatures is now in deep crisis. A global assessment by the International Union for Conservation of Nature (IUCN) says that of the world's 127 shallow-water coral reef ecosystems, 122 — about 96 percent — are at extremely high risk.

Alongside heat stress caused by climate change, overfishing and pollution are making the crisis more severe. The study warns that most of the world's coral reefs could collapse by 2075.

This figure does not, however, mean that 96 percent of the world's corals have already died. It means that most of the assessed ecosystems are at a level of risk where, if current trends and future climate conditions continue, they could collapse.

That distinction matters, because researchers believe there is still an opportunity to take effective action for the reefs that can still be protected and restored.

Coral reefs cover a very limited area compared with the world's ocean floor. Yet this small area shelters a vast number of marine animals. Reefs are often called the 'rainforests of the sea' — their complex structures provide food, shelter and breeding grounds for fish, invertebrates and other marine life.

Coral reefs are also vital for coastal communities. In many parts of the world, fishing, tourism and local businesses depend on these ecosystems. The natural structures built by corals also reduce wave energy, protecting coasts from erosion and storm damage.

The decline of coral reefs is therefore not only a loss for marine animals; it is the weakening of a natural system on which environmental balance, human livelihoods and economic security are closely intertwined.

The IUCN assessment identifies climate change as the most important long-term threat to coral reefs. As ocean temperatures rise and marine heatwaves grow in intensity and frequency, corals are losing their ability to survive in their natural environment.

The main builders of coral reefs are tiny animals called coral polyps. Photosynthetic algae living inside them play an important role in supplying corals with food and energy. When water temperatures stay above normal for a long time, corals may expel these algae — an event known as 'coral bleaching'.

A bleached coral may look white, but that does not mean it has died immediately. If favourable conditions return, some corals can recover. But if heat stress lasts long, or bleaching recurs within a short span, the coral's food supply is disrupted, disease risk rises and mortality can increase.

The problem is that in many cases reefs are not getting the time they need to recover. Successive marine heatwaves are damaging corals anew, weakening the recovery capacity of the entire ecosystem.

The IUCN assessment of 22 October is the first full global assessment of coral reef ecosystems under the global Red List of Ecosystems framework. It considered data on past environmental change alongside forecasts of future climate conditions.

Under the moderate climate scenario used in the assessment, global temperatures could rise by about 2.7 degrees Celsius by 2100 compared with pre-industrial times. Analysing possible heat stress from 2026 to 2075 under this scenario, 121 reef regions were placed in the highest risk category. Including other indicators of past decline, 122 regions overall were classified as 'Critically Endangered'.

Here, 'Critically Endangered' does not mean the extinction of a species, but an extremely high risk of the ecosystem collapsing. The researchers considered both roughly 50 years of past change and future heat stress.

Considering past change alone, 30 of the 127 regions — about 24 percent — would have fallen into this highest risk category. Adding forecasts of future climate conditions made the risk picture far more serious.

The result should not, however, be read as a certain future — climate model forecasts depend on possible scenarios. It is primarily a warning, so that action can be taken now.

The crisis is not limited to climate change alone. Local pressures such as overfishing, coastal development, pollution, uncontrolled tourism and storms also put great pressure on coral reefs.

The IUCN assessment found that in 63 percent of reef regions there is pressure disrupting the balance between fish and other organisms. Parrotfish, in particular, help maintain ecological balance on many reefs by eating algae; if overfishing reduces their numbers, algae can spread and the space available for new coral settlements can shrink.

Sediment and pollutants entering the water from coastal construction also add pressure on corals. Nutrient-rich waste from farms and urban areas, untreated sewage and tourism-related damage can weaken coral health at the local level.

The researchers' conclusion is clear: just as reducing global warming is essential, so is controlling pollution, overfishing and habitat destruction locally. If action is taken in time, at least part of this colourful underwater world may still be saved.