Coral reefs are home to around 25 per cent of all marine species and provide approximately 2.7 trillion dollars a year in goods and services, of which 36 billion dollars comes from tourism alone. They protect and ensure the wellbeing of coastlines and provide food and economic support to hundreds of thousands of people. Yet they are disappearing: in the decade between 2009 and 2018, the world lost 14 per cent of this ecosystem. Although corals occupy 0.2 per cent of the ocean, their disappearance would cause catastrophic damage.

The largest analysis of corals ever conducted

An environment so rich in life and yet so fragile. The figure emerging from the report "Status of coral reefs of the world: 2020" is deeply troubling: in the last ten years we have lost around 12,000 square kilometres of coral, the equivalent of more than the entire Australian coral reef. The enormous work behind this study, which has been ongoing for around forty years, involved three hundred scientists who collected almost two million data points, observing corals at more than 12,000 sites across 73 countries. The analyses were based on live coral cover, which indicates the health of the reef, but also on the presence of algae, a highly significant indicator of coral stress. It was observed that from 2010 to 2019 algae presence increased by around twenty per cent.

Coral reefs around the world are under constant stress caused primarily by climate change. The warming of waters is one of the factors that triggers coral bleaching, which inexorably leads to their disappearance. As far back as 1998, around eight per cent of coral reefs had been destroyed by the first major bleaching event; nevertheless, in the years that followed, much of the coral managed to recover.

Why bleaching leads to coral death

Let us take a step back. Coral is formed from the calcareous skeletons of polyps, which form gigantic colonies of identical clones that secrete skeletons of widely varying shapes and sizes. Coral polyps have no colour of their own; rather, their colour is provided by the symbiotic organisms living inside their cells, the zooxanthellae. These are photosynthetic organisms that supply the polyps with the nutrients they need but cannot obtain on their own. However, when the water temperature is too warm, the zooxanthellae sustain damage to their photosynthetic system, which ceases to function. They also produce reactive oxygen molecules that damage the cells of the polyp, which, as a defence response, expels them. The result is a loss of colour — bleaching — of the corals. No longer having the nutritional support they need, the corals die.

Signs of hope are not absent

The report highlighted that although in the last decade the interval between bleaching events has not been sufficient to allow corals to recover and reform, in 2019 a recovery of coral reef cover of two per cent was observed. This indicates that coral reefs are still resilient, and so strategies to reduce pressures on this ecosystem must be put in place immediately. Perhaps, in the coming decades, they will be able to flourish once more as they did before 1998.

People are heavily dependent on coral reefs around the world. We must focus and increase our efforts to safeguard them. We must keep them functioning so that they can continue to sustain communities.

David Obura, lead author of the study