CORAL REEFS ARE THE RAINFORESTS OF THE SEA, occupying less than 1% of the ocean floor but supporting nearly 25% of all marine species. A healthy reef is like a bustling city, teeming with fish and turtles, as well as a multitude of invertebrates. Shrimps, crabs, brittlestars and worms, cohabit with slugs, snails and squid. But these marine utopias are disappearing before our very eyes. In the past three decades alone, around 50% of corals have been lost, with the latest forecasts suggesting that over 90% of reefs will be gone by 2050. Some problems are local in scope, such as dynamite fishing, or pollution (e.g. from agricultural fertilisers or sunscreens that wash off peoples’ skin). Other problems are global, such as the threats of ocean acidification and warming.


The majority of the heat trapped by greenhouse gases – a whopping 93% – is absorbed by the world’s oceans. That means the more fossil fuels we burn, the warmer our seas become. According to one study, 2019 was the hottest year on record for the world’s oceans. That may sound like a happy outcome for beachgoers, but the same cannot be said of coral. Although it thrives in warm water, it has thresholds. The Intergovernmental Panel on Climate Change warns that coral reefs will likely decline by 70-90 percent if global average temperatures reach 1.5°C above pre-industrial levels. If we overshoot that and hit 2°C, virtually all coral (more than 99 percent) will be lost. The scary part? We’re already at 1°C above pre-industrial levels and on track to hit 1.5°C around 2040.

Why does temperature change have such an adverse effect on corals? The answer lies in an ancient mutualistic alliance between corals and algae. For at least 160 million years, certain types of algae – also known as zooxanthellae – have been living inside the bodies of corals. There, they convert sunlight into nutrients, which sustain their hosts. The algae get shelter, while the coral gets food. It’s a win-win. And it’s also why we love looking at pictures of coral reefs – the algae are responsible for bestowing the corals with their pleasant pop of colour.

However, when corals become heat-stressed, they expel their photosynthetic companions. Not only does this cut off the corals’ food supply – leaving them vulnerable to starvation and disease – it also robs them of their attractive hues. The resulting white coral is said to be ‘bleached’.

Mass Bleaching

Some corals can bounce back from bleaching events, but only when given a chance to recover. This process can take 10 to 15 years, and relies on the water temperature returning to a cooler baseline. However, when bleaching is severe, with little time between episodes, the chances of recovery become sketchy at best. Reefs turn into underwater ghost towns.

Global mass bleaching events are now a source of serious concern. The most recent event, between 2014 to 2017, was the worst on record, with over 70% of the world’s reefs affected. Australia’s great barrier reef was hit especially hard, with two back-to-back marine heat waves in 2016 and 2017 killing two thirds of its coral. The latest data, released in April 2020, shows an even bleaker picture. For the first time in history, there is coral bleaching along the entire 1,500 mile length of the Great Barrier Reef.


Coral Gardening

Environmental activists and marine biologists across the world are scrambling to find ways to save our remaining reefs. One of the biggest instruments in their toolkit is “coral gardening”. It involves mass-producing live corals in nurseries and transplanting them back into degraded reefs. In the Caribbean, for example, coral nurseries play a key role in the restoration of staghorn and elkhorn corals. The fragments are taken from healthy reefs and each one grows just like a cutting from a plant. Hung from ‘propagation trees’ or laid out on tables, these cuttings are grown until they’re large enough to be ‘outplanted’. In other words, attached to damaged or over-stressed reefs, helping to speed their recovery.

Meanwhile, scientists from the Australian Institute of Marine Science (AIMS) are looking at ways coral strains can be cross-bred to produce so-called ‘super corals’ (the ‘super’ part comes from their ability to withstand higher water temperatures).

Artificial Reefs

If it’s not enough to jump-start reefs then conservationists can try building them from scratch. Artificial reefs are man-made structures that are either deliberately or unintentio­nally submerged underwater. In the right marine environment, you can pretty much sink anything solid – concrete structures, old tyres, wrecked ships and planes – and corals can form on it. Reefs have even developed on structures as unexpected as decommissioned subway cars and vintage battle tanks. The responsible creation of artifi­cial reefs serves the dual purpose of waste disposal while benefitting the environment and tou­rism industry. Over decades, these defunct objects become encrusted with life, turning human scrap into natural wonders (many examples can be viewed in our feature story about artificial reefs here).

However, the creation of artificial reefs can be a bit hit-and-miss. Which is why, in the 1970s, marine scientists Thomas Goreau and Wolf Hilbertz developed ‘biorock’ technology. By running a low-voltage current through a steel structure immersed in seawater, a hard shell of limestone – the key ingredient in coral – quickly forms. You can then attach coral fragments to it, and the limestone substrate helps the coral grow five times faster than normal. Today, biorock projects are assisting with coral conservation all over the globe.

Predator control

On the Great Barrier Reef, scientists are working to control the numbers of crown-of-thorns starfish. These marine invertebrates – which get their name from their venomous spines, have a voracious appetite for coral. Each one ingests 10 square metres of it per year. And there are more than five million of these starfish patrolling a stretch of the reef between Cairns and Cooktown. When populations reach outbreak levels, marine scientists spring into action. They either physically remove the starfish, or cull them there and then, by chemical injection. Another – more natural weapon – is to breed and introduce the rare giant triton, a large marine snail that preys on the starfish. In a new effort, robot drones have been deployed to disptach the starfish, while also monitoring coral bleaching, water quality, pest species, pollution and sediment buildup.


Reef Visions

Dutch photographer Georgette Douwma has photographed coral reefs for as long as she can remember. “I’ve always been drawn to coral reefs,” she says. “To watch them die would be a tragedy.” Looking for a way to develop her work in new directions, Douwma began experimenting with what she calls ‘coral kaleidoscopes’ – duplicating and reduplicating her images in a fashion not too dissimilar from the way the corals themselves proliferate. As well as reproducing sexually, corals can propagate by cloning themselves. Break a fragment from a coral and reattach it to the seafloor, and that fragment will mature into a new, yet genetically identical clone.

Douwma is now in the business of cloning corals herself – albeit in photographic form. Motivated primarily by aesthetic values, she creates arresting compositions with strong symmetry, texture and design. “My ultimate aim is to capture something that is greater than the sum of its parts,” she says. “Something that can communicate the vibrancy and colour of healthy reefs, before the next big bleaching event happens.” The resulting pieces bring to life in spectacular fashion the underwater edens that we stand to lose, unless we can find a way to slow global warming.

More of Douwma’s coral kaleidoscopes can be seen in our feature story here.

Coral Rainbow

The amazing diversity of colour in coral reefs is one of the main reasons we’re so drawn to them. To celebrate their beauty we’ve put together some fun facts that will take you through the whole spectrum of the coral rainbow. At the time of writing, rainbows have become a symbol of solidarity for a world weighed down by the COVID-19 pandemic. Perhaps those of you who are home schooling will find this an inspirational resource to teach your kids some cool coral facts. Take a look here.


Ocean warming is killing corals and we need solutions. Reefs support the livelihoods of half a billion people, and provide $30 billion annually in goods and services, including significant tourism revenue. They act as natural breakwaters, providing protection against storms for many coastal communities. Moreover, up to a third of all marine species rely on coral reefs for their survival. Their loss would undoubtedly ripple out into human societies that depend of these species as a source of protein. Scientists worry that the loss of reefs, and the species they support, could evolve into a humanitarian crisis.

We have tools at our disposal, and a wide range of innovative measures to help coral reefs withstand the pressures of global warming. But these measures can only go so far. If all we do is address the symptoms and not the cause, then our progress will likely be overshadowed. The scientists who conducted the latest survey of the Great Barrier Reef summed it up earlier this month:

“The Great Barrier Reef will continue to lose corals from heat stress, until global emissions of greenhouse gasses are reduced to net zero, and sea temperatures stabilise. Without urgent action to achieve this outcome, it’s clear our coral reefs will not survive business-as-usual emissions.”

Where there’s a will, there’s a way.

On 1st April 2020 an international team of the world’s leading marine scientists across 10 countries, laid out a roadmap for an ocean renaissance, that will help marine life recover to full abundance by 2050. The study identifies specific interventions, including protecting large swathes of ocean, sustainable fishing and pollution controls, and mitigating climate change. The measures would cost billions of dollars a year, the scientists say, but would bring benefits ten times as high. New innovations are being proposed all the time – including the use of satellite technology to protect coral reefs.

Tuesday, 8th June 2021 is UN World Oceans Day.  This year’s theme is “The Ocean: Life and Livelihoods”, launching  a decade of challenges to achieve Sustainable Development Goal 14 to “conserve and sustainably use the oceans, seas and marine resources” by 2030.

View our full coral reefs gallery here.