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Preserving corals could save billions in coastal defences – new study

In 2005, Hurricane Wilma whipped up 13-metre waves off the coast of Mexico. Yet when the waves reached the Caribbean sea’s Meso-American coral reef, the natural structure sucked 99 per cent of their power. 

This isn’t an isolated incident. Scientists have found that not only do reefs reduce wave energy by an average of 97 per cent.

Nearly 40 per cent of the world’s population lives within 100 kilometres of the coast, and that figure is set to rise. As the risk of extreme weather events like floods and tropical stormsincreases, so does the danger to populations and their livelihoods.

Protecting coastlines is big business, and the cost of building defences is expected to rise significantly by the end of the century. So natural solutions could provide cost-effective options for adapting to the effects of climate change.

In a new paper in the journal Nature Communications, scientists have collected available data on the role coral reefs could play in reducing climate risks to coastlines.

They found that reefs perform as well as artificial defences like breakwaters, reducing wave energy by an average of 97 per cent. Better still, they’re relatively cheap. The paper shows that restoring reefs costs one tenth of the outlay for building tropical breakwaters.

Collecting data

For the first time, scientists have collected all the available data on how much reefs can do to protect coastlines. Author Dr Michael Beck from The Nature Conservancy and UC Santa Cruz tells Carbon Brief:

“We looked for all available studies that measured waves before and after they passed over reefs and did a meta-analysis of these studies, just as you would say for a medical examination of a question examined by many researchers. We also gathered data on the costs of building artificial breakwaters and reef restoration. Finally we did global spatial analyses to examine how many people globally may receive risk reduction benefits from reefs – you can see maps and data here.”

The researchers pieced together data from over 250 different studies. They examined which parts of the reef do best at dissipating wave energy, finding that reef crests – the part of the reef closes to the sea – are the most effective at taking the force out of waves, absorbing around 86 per cent of a wave’s energy.

Reef flats – the shallows of the reef, which extend towards the shore – dissipate around 65 per cent of the remaining wave energy. Overall, the whole reef reduces wave energy by around 97 per cent.

In fact, the researchers found that reefs provided as much protection as manmade coastal defences, like breakwaters. But reefs far outperform breakwaters when it comes to cost-effectiveness. The median cost of building tropical breakwaters is $19,791 million. Compare that with a median of $1,290 million for restoring a coral reef.

The paper notes estimates that up to 197 million people living near reefs benefit from their protection – often in poor countries with less capacity to adapt to the effects of climate change.

That’s 197 million who could suffer if reefs are allowed to degrade. This is already a problem for some regions – the paper points to the Maldives, where the loss of corals has led to “real increases in wave energy reaching coastlines”.

Reefs

Natural capital 

The researchers are clear that there still isn’t enough research out there on coral reefs’ protective properties. But the results of their meta-analysis indicate that reefs aren’t just beautiful natural environments – they also perform an important role in protecting coastlines – performing as well as the most effective breakwaters. Healthy reefs can even fix themselves after heavy storms.

That’s all well and good, but there is plenty of research indicating the effects of climate change, from ocean warming to increased acidification, are putting corals at greater risk. However, the paper says these risks may be exaggerated. Says Beck:

“Reefs face many growing pressures from development and climate change and some question their viability in future centuries. We make the case that this is too pessimistic. There are many reasons for optimism about the future of coral reefs particularly if we manage other local stressors.”

It’s possible that factors like blast fishing and pollution are more significant threats than climate change, the paper says – stresses that can be eased with the right policy approaches.

Like mangroves, marshes and oyster reefs, corals are pre-existing protective structures that shield coastal communities from the impacts of storms and floods. They are part of the earth’s natural capital – and this new research suggests people all around the world may suffer if they are allowed to degrade.

Reposted from: http://www.carbonbrief.org/blog/2014/05/coral-reefs-cheap,-effective-coastal-defences/