A coral reef with fish swimming around

Coral reef coverage has declined significantly since the 1950s ©Mayumi.K/Shutterstock.com

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Over half of coral reef cover across the world has been lost since 1950

Coral reefs have declined by over half since the 1950s as they suffer from the effects of climate change and overfishing.

Across the world, the area that coral reefs occupy has fallen by 50% in the half century from 1957. Their ability to carry out key roles, such as food provision and locking away carbon, has fallen too.

Corals may be able to recover, but it will require a concerted effort to protect reefs from fishing and limit the impact of climate change. The research, led by the University of British Columbia, is published in the journal One Earth

Dr Tyler Eddy, the lead researcher of the study, says, 'It's a call to action - we've been hearing this time and time again from fisheries and biodiversity research.

'We know coral reefs are biodiversity hotspots. And preserving biodiversity not only protects nature, but supports the humans that use these species for cultural, subsistence and livelihood means.' 

Bleached coral

Corals bleach as a stress response, and can lead to death if too frequent. Image by Vardhan Patankar, licensed via Wikimedia Commons CC BY-SA 4.0.

Coral calamity 

Coral reefs are one of the most important underwater habitats. While tropical corals are the most well-known, coral reefs exist in a variety of places. Even the UK has cold water reefs off the coasts of Cornwall and Scotland. 

This new study focused specifically on tropical corals, which are important for both aquatic species and humanity as a source of food in the ecosystem. Corals do so by forming skeletons of calcium carbonate, which provide reefs where species can shelter and breed. 

But these skeletons make corals vulnerable to rising carbon dioxide levels in the atmosphere as the gas dissolves into seawater and makes it more acidic. This dissolves corals' calcium carbonate structures, which in turn reduces the amount of carbonate available for corals to build the skeletons back again. 

Warming temperatures are also a risk, as spikes in temperatures cause corals to eject the photosynthetic algae that live inside them. While these events, known as bleaching, are a normal stress response for corals, they are becoming more frequent. Repeated bleaching can cause corals to die. 

Studying the period between 1957 and 2007, the researchers found that the coverage of living coral on reefs had fallen by around 50%. Most countries showed a decline of up to 6.8% per decade though a few, including Japan and Malaysia, showed increases during the period. 

As coverage declined, this had impacts on the species that are supported by coral. The biodiversity of reefs was found to have declined by 63%, while the abundance of fish species fell by 60%. 

In many cases, the exact extent of the losses are unknown as historic records on the condition of reefs in the 1950s and 60s in many areas of the world are often lacking. While this has improved with time, some areas of the world still have limited records available to analyse. 

Fishermen on a boat above a coral reef.

Many people around the world depend on coral reef fishing for their survival and livelihood ©Ethan Daniels/Shutterstock.com.

Fishing falls 

While the impact on the corals themselves is severe, the impact on the people who depend on them is also is also taking a significant toll. 

Fish form a large part of the diet for many people, while it is estimated that around six million people depend on fishing coral reefs for their livelihood. 

This new analysis found that many people's diets and livelihoods are already being affected by the changes in coral reefs. Since 2002, catches have been declining year-on-year even though fishing effort has been increasing.  

Co-author Dr Andrés Cisneros-Montemayor says, 'It's heart-wrenching for us to see photos and video of wildfires or floods, and that level of destruction is happening right now, all over the world, to coral reefs. 

'It is threatening people's culture, their daily food, and their history. This isn't just an environmental issue, it's also about human rights.' 

Steps are being taken to protect coral reefs, with efforts to restore them through transplanted corals grown elsewhere, or to artificially cool them with pumps.

Work is also being undertaken to protect fisheries, with protected areas and quotas being introduced in an attempt to allow the reefs to recover. 

However, the efficacy of these steps varies, and so the researchers have called for a global effort to combat the mix of issues that affect coral reefs.

They hope to see an integrated approach between the nations of the world on climate, biodiversity and fishery policy to help turn around the declines that reefs are currently experiencing.