Coral reefs cover less than 0.1% of the ocean floor, but they’re home to a quarter of all the marine species on Earth. This makes them incredibly biodiverse ecosystems, supporting a complex food web of organisms that includes us humans.
Around 850 million people around the world are thought to rely on coral reefs for their food and livelihoods. Healthy reefs directly support around 30 million small-scale fishing jobs. Reef tourism is a £36 billion industry, providing work for thousands of people in some of the world’s poorest countries.
As well as helping to fill our bellies, reefs also feed our souls. They are central to the cultures of many Indigenous People, and a source of wonder for all of us who love the natural world. Coral extracts are increasingly being used to improve our physical well-being too, providing treatments for asthma, arthritis, cancer and many other diseases.
These huge living structures even provide humanity with a physical barrier from harm. Research has shown that coral reefs reduce wave energy by as much as 95%, giving coastal communities vital protection from tsunamis and storms.
In short, the importance of our coral reefs is enormous. Unfortunately, so are the threats they face.
Why should we worry?
The Earth has warmed by an average of 1.2°C since pre-industrial times, and in the last 40 years we have lost 50% of our coral reefs.
If average global temperature rises by 1.5°C, the loss will be somewhere between 70% and 90%. In a world with 2°C of warming, only 1% or our coral reefs will remain.
Most of this destruction is being done by cyclones, which become more powerful and frequent as the climate warms. Further damage comes in the form of ‘coral bleaching’. Healthy reefs get their bright colour from the microscopic algae that live in a coral's hard external structure. These algae help to produce food for their hosts but if the surrounding water gets too warm, the algae leave. This takes away the coral’s main food source, as well as its colour. Reefs can survive short periods of bleaching but, long term, the situation is fatal.
Other threats come from people drilling for oil, building ports, dredging, shipping and, of course, fishing. Discarded fish traps, nets and other debris can seriously damage coral reefs, and over-fishing certain species has a major impact too. For example, some fish eat marine algae – so if too many of these fish are taken from the reef, the algae can overwhelm the coral it lives on.
And then there’s the knock-on effect of farming. When nitrogen fertilizer runs off fields into the ocean, it causes huge increases in algae. This algae is then eaten by the larvae of crown-of-thorns starfish, causing a population explosion. Just one adult crown-of-thorns starfish can eat as much as 9.5 metres of living coral a year. During an outbreak in 2015, the Great Barrier Reef was home to somewhere between 4 and 12 million of them.
Why should we be hopeful?
So, how can we help coral reefs survive? Tackling climate change is the biggest step and that means drastically reducing our greenhouse gas emissions. At the same time, we must accept that it won’t be possible to save some reefs. Which makes it all the more important to look after those that we can.
In some parts of the ocean, cold currents rise up from the depths, cooling the surface water. As a result, reefs in these areas are more resilient to climate change. If we protect them, they could eventually regenerate reefs in other areas. This is because coral larvae are dispersed across the world on ocean currents. So, when larvae from a resilient reef arrive at a dying one, they could take hold and rebuild it.
These resilient reefs are often close to communities that face challenges of their own. For some fishers and farmers, looking after coral may feel like a secondary concern compared to the immediate pressure of making ends meet. That’s where initiatives like Coral Reef Rescue come in. It’s a partnership of scientists, organizations like WWF and communities working to improve education, opportunities and food security for these communities. The ultimate aim is to give people the tools and resources they need to protect their own natural resources.
Data is another key tool in our belt. Members of the UN Convention on Biological Diversity are now measuring their reefs’ size, live coral cover and the number of fish they support. By checking their progress against global biodiversity targets, these nations can see which interventions are really working and focus their conservation work more effectively. This approach also makes global and regional data more consistent, giving a more reliable picture of how reef systems change over time.
The next generation of coral
Florida’s Coral Restoration Foundation is taking more direct action. Here, divers are growing new coral in underwater nurseries, ready to be replanted on damaged reefs. Meanwhile, scientists at the University of Hawaiʻi at Mānoa are studying a more controversial approach, called ‘assisted evolution’. This involves finding corals that seem more resilient to warming, and bringing them into the lab for exposure to even warmer water. If they can adapt to the increased temperatures, these more resilient corals might be used to breed stronger generations of coral for the future.
So, while there’s no doubt that the threats to our coral reefs are serious, with a concerted effort, we can help to turn the tide.