Infrastructure protectionCoral reefs offer valuable protection for coastal infrastructure

Published 14 May 2014

Growing natural hazards from coastal storms, flooding, and rising sea levels are leading to major investments worldwide in coastal defense structures such as seawalls and breakwaters. A new study shows that coral reefs can provide risk reduction benefits comparable to artificial defenses, and reef restoration and enhancement is a cost-effective alternative to manmade structures. Restoring coral reefs as a way to protect coastal infrastructure is also cheaper: the typical price for a tropical breakwater project is $197 million, compared with $129 million for restoring a reef.

Growing natural hazards from coastal storms, flooding, and rising sea levels are leading to major investments worldwide in coastal defense structures such as seawalls and breakwaters. A new study shows that coral reefs can provide risk reduction benefits comparable to artificial defenses, and reef restoration and enhancement is a cost-effective alternative to manmade structures.

The study, published 13 May in Nature Communications, was co-led by Michael Beck, lead marine scientist for the Nature Conservancy and a research associate at the Institute for Marine Sciences (IMS) at UC Santa Cruz.

We show that reefs can be particularly cost-effective as a first line of defense in comparison to artificial structures,” Beck said. “We now have solid numbers to show just how important reefs are in reduction of wave energy. This is an issue that matters to hundreds of millions of people.”

A UCSC release reports that the researchers performed a systematic search of the scientific literature and analyzed published data on the contributions of coral reefs to risk reduction. The combined results showed that coral reefs dissipate 97 percent of the wave energy that would otherwise impact shorelines. Wave energy is a key factor in storm damage and coastal erosion. The researchers also found that most of the wave energy (86 percent) is attenuated by the reef crest, an important finding for guiding reef restoration efforts, Beck said.

Overall, this natural shield leads to a reduction in wave height of 64 percent on average, comparable to a reduction of 30-70 percent accomplished by a program of artificial detached breakwaters, according to the study.

USA News reports that Beck’s group also did a rough cost assessment: the typical price for a tropical breakwater project was $197 million, compared with $129 million for restoring a reef.

The UN Intergovernmental Panel on Climate Transform (IPCC) estimated last September that sea levels would rise by 26-82 centimeters (10-32 inches) by 2100, driven partly by ice melt and partly by expansion of the ocean as it warms.

Spending on dikes alone is predicted to rise to $12-71 billion by 2100, according to an estimate published in the Proceedings of the National Academy of Sciences (PNAS) earlier this year.

A 2011 report by the UN International Approach for Disaster Risk Reduction, 3.6 percent of the world’s gross domestic product (GDP) was annually exposed to tropical cyclones in the 1970s.

This rose to 4.3 percent of GDP in the first decade of the twenty-first century.

Coral reefs face many threats — such as climate change, ocean acidification, coastal development, and destructive fishing practices — but Beck said there is still cause for optimism.

People forget that coral reefs currently are in better shape than any other coastal habitat. We’ve lost more of our oyster reefs, marshes, and mangroves, so there’s still a lot of coral reef habitat to work with,” he said. “It’s time to start taking action to preserve and restore this first line of defense for coastal hazard reduction.”

The researchers estimated that there are nearly 200 million people living in coastal areas where they may benefit from the protection afforded by coral reefs, or bear the cost if reefs are lost or degraded.

Beck is currently working with a UCSC postdoctoral researcher, coastal engineer Borja Reguero, on a joint TNC-UCSC effort to design a coral reef restoration project for coastal defense in Grenada.

We can do things to rebuild the structure of a reef and help kick-start the growing of living corals on top. We think that can be a particularly cost-effective approach for rebuilding this first line of defense,” he said.

The researchers note that conservation efforts have most often been directed to more remote reefs, but the study suggests there should also be a focus on reefs closer to the people who will directly benefit from reef restoration and management. In terms of number of people who would receive risk reduction benefits from coral reefs, the top fifteen countries include:

  • Indonesia, 41 million
  • India, 36 million
  • Philippines, 23 million
  • China, 16 million
  • Vietnam, 9 million
  • Brazil, 8 million
  • United States, 7 million
  • Malaysia, 5 million
  • Sri Lanka, 4 million
  • Taiwan, 3 million
  • Singapore, 3 million
  • Cuba, 3 million
  • Hong Kong, 2 million
  • Tanzania, 2 million
  • Saudi Arabia, 2 million

— Read more in Filippo Ferrario et al., “The effectiveness of coral reefs for coastal hazard risk reduction and adaptation,” Nature Communications 5, article number: 3794 (13 May 2014) (doi:10.1038/ncomms4794); and Jochen Hinkel et al., “Global Climate Impacts: A Cross-Sector, Multi-Model Assessment Special Feature — Social Sciences — Sustainability Science — Physical Sciences — Sustainability Science,” Proceedings of the National Academy of Sciences 111, no. 9 (3 February 2014): 3292-97(doi:10.1073/pnas.1222469111)