The causes of coral reef collapse - and how to save our 'rainforests of the sea'

A living kaleidoscope of colours, shapes and textures that form inspiring underwater gardens and landscapes.

A magical world of over 800 species of reef-building corals hidden beneath the waves, home to an estimated 32 per cent of all named marine species, excluding microbes and fungi.

This level of diversity is particularly impressive given that reefs cover less than 0.1 per cent of the surface area of the ocean. Coral reefs are rich in symbiotic relationships among species, honed by millions of years of evolution.

Scuba divers swimming next to a stonefish in the Similan Islands in the Andaman Sea off Thailand's Phang Nga province. Picture: Sebastien Berger/AFP via Getty Images

These ‘rainforests of the sea’ play a vital role in our existence above water. They support the lives of up to one billion people and provide ecosystem services valued at $9.9 trillion [£7.3 trillion] annually through fisheries, tourism and coastal protection.

That is why protecting and restoring coral reefs is not only a moral imperative, but also a smart economic choice. Investment in coral reef-positive businesses has the potential for phenomenal returns for impact investors. It is one where the returns far outweigh the costs, while inaction carries a steep price.

The causes of coral collapse

Corals rely on tiny algae, known as zooxanthellae, for nourishment and for their splendid colours. When stressed under warming temperatures or other environmental pressures, these algae leave, causing coral bleaching.

Prolonged or frequent separation leads to coral starvation and death. But bleached coral is not dead coral and can recover if the stressor is removed.

While coral reefs have thrived for 50 million years, most coral reefs today are on the brink of disappearing.

There are many reasons, including natural disasters and growing pressures from destructive fishing and unsustainable coastal development.

Industrial animal farming can add to these. The agricultural runoff of fertilisers and pesticides, which together with soil erosion and sediment, end up in waterways cause nutrient pollution and lead to harmful algal blooms that deplete oxygen levels and block sunlight to the reefs.

In addition, there are concerns that antibiotics and hormones, used in animal farming, could further disrupt natural marine ecosystems, negatively impacting the health of coral reefs and the species that depend on them.

There is little doubt that the rise in industrial agriculture for both crops and farmed animals has led to a massive spike in pollution from excess nitrogen and other nutrients lost to the environment.

UNEP’s new interactive briefing on beating nitrogen pollution, describes nitrogen pollution as “one of the most pressing pollution issues facing humanity, threatening our environment, health, climate and ecosystems”.

Climate change is the final blow for reefs, causing ocean temperatures to rise, leading to coral bleaching. Our food is responsible for about a third of greenhouse gas emissions; that’s more than any other sector. Animal agriculture alone is responsible for more greenhouse gas emissions than the world’s transport sector.

The ocean’s warming is now contributing to the fourth mass bleaching event, affecting an estimated 80 per cent of the world's reefs.

Wake up world

Healthy nurseries of tropical coastal fish stocks are turning into zombie ecosystems. Six years ago, the Intergovernmental Panel on Climate Change (IPCC) projected the death of over 90 per cent of all coral reefs by 2050 if average global air temperatures warm by 1.5C above pre-industrial values. A 99 per cent decline was projected at 2C of warming.

Today, even if all climate commitments by world governments are respected, we will be on an unfortunate track for almost 3C warming.

It's time to repair what we've broken and invest in what we've taken for granted. With today's scientific knowledge and technology, we have a fighting chance to do that. By mobilising resources, we can restore many of these vital reefs through positive interventions on land.

Governments and businesses, including insurance agencies, are finally waking up to this urgent challenge. We've seen a surge of initiatives in recent years to prevent coral reefs from disappearing, and many are already having a tangible impact.

One of the largest to do so is the Global Fund for Coral Reefs (GFCR), the first blended finance structure dedicated to coral reefs and related ecosystems like mangroves and seagrasses. Public, private and philanthropic capital is coming together to create a portfolio of market-based solutions spanning over 20 countries.

Private businesses benefiting from investments are those that reduce stress on reefs or actively protect, transform, restore and recover them. This includes sustainable fishing, ecotourism, waste treatment and recycling enterprises.

Yet much more would be needed to reach the ambition of protecting at least three million hectares of coral reefs globally by 2030 – about 12 per cent of remaining reefs.

Prevention is better than cure

Establishing sustainable finance mechanisms, including those linked to revenue sources from reef-positive businesses and payment for ecosystem service models, can provide long-term funding streams and incentivise better business practices in coral-dependent industries, like fisheries and tourism.

Any risks associated with such investments are dwarfed by their immense potential and the cost of inaction. Fish-based food systems and livelihoods depend on healthy coral reefs. Avoiding worse ocean-born hurricanes, which cost hundreds of billions of USD only in the past months, requires healthy coral reefs that can absorb an incredible 97 per cent of wave energy.

There is a clear business case to be made for investing in coral protection. Continued innovation, collaboration and investment will ensure these vital ecosystems survive the changing climate in the decades to come.

Our legacy to future generations must not be the demise and death of these extraordinary, magical and highly valuable coral reefs.

- Susan Gardner is director of the ecosystems division of the United Nations Environment Programme, while Philip Lymbery is global CEO of Compassion in World Farming International and a former United Nations food systems champion.