Coral Bleaching Event Can Increase Flood Risk, Economic Losses

By Coastal and Marine Hazards and Resources Program August 9, 2023

Coral showing signs of bleaching — A colony of fire coral about 5 feet underwater in Dry Tortugas National Park in the Gulf of Mexico shows signs of bleaching from recent extreme water temperatures. Photo taken July 26, 2023, by Lauren Toth, USGS.

Coral death and loss of reef-building corals due to the 2023 heat-related coral bleaching events in Florida and elsewhere in the Caribbean and the Gulf of Mexico will have far-reaching and lasting effects. Beyond the immediate loss to a thriving ecosystem, the loss of living corals degrades the reef structure, leaving coastal communities along reef-lined coasts to face increasing risks from coastal flooding hazards. The USGS and partners have shown that projected coral reef degradation in Florida could increase the coastal flood risk to more than 7,300 people at the cost of $823.6 million annually.

These changes are being accelerated by the ongoing (2023) coral bleaching event. “Unfortunately, coral bleaching had become the new normal for many coral reefs, including the reefs in south Florida” said Lauren Toth, USGS Research Physical Scientist. "But what’s really troubling about this event is that this year, the water isn't just warmer than any year on record, but also the warming started in July rather than late August, when we typically see coral bleaching. To survive, corals will have to endure a lot more heat stress than they’re used to, and many may not make it."

Coral reefs are known for their natural beauty, biodiversity, and support of important local fisheries, but their value and importance extend even further. They provide significant social and economic benefits by reducing the impact of coastal storms and flooding on nearby communities. Reefs act as a natural buffer, absorbing and dissipating wave energy, thus reducing the force and potential damage caused by waves and storm surges.  

Coral Reefs Act as Natural Buffers for Storm Energy

Degradation of coral reef structures has led to increased erosion of the seafloor. The loss of seafloor both in volume and elevation has accelerated the rate of relative sea-level rise in Florida at the regional scale, USGS-led research shows. This coral degradation and erosion of the coral reefs, in turn, allows for larger waves and storm surges, increasing coastal flooding.

"Florida's coral reefs serve as a natural barrier against coastal flooding, shielding coastal communities from the destructive forces of storms and hurricanes,” said Curt Storlazzi, USGS Research Geologist. “Understanding the social and economic value of these reefs allows informed decisions to be made about preserving and restoring them to reduce coastal risks to, and increase the resiliency of, coastal communities."  

USGS has produced a spatially explicit and rigorous valuation of the protection provided by Florida's coral reefs. By identifying the areas where coral reef degradation would have the most substantial impact on coastal flood reduction, stakeholders and decision-makers can gain crucial insights into the urgent need for reef management, recovery, and restoration. 

Video Transcript

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Coral reefs act like submerged breakwaters by breaking waves and dissipating their energy offshore before they flood coastal properties and communities. This is an enormously valuable function: In 2017, Hurricanes Harvey, Irma and Maria alone caused over $265 billion in damage across the nation. USGS Research Geologist Curt Storlazzi explains how healthy coral reefs in places like the Caribbean and Pacific Islands serve as national, natural infrastructure. Restored reefs not only support critical biodiversity and coastal economies—they also reduce flood risks to coastal communities from storms and sea-level rise. Listen to the audio-described version.

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View audio described version. En español. Three new reports from the U.S. Geological Survey, the University of California and the National Oceanic and Atmospheric Administration quantitatively assess how coral reefs damaged by those hurricanes increased flood risk significantly, to the tune of hundreds of millions of dollars. The reports also assess how, in the absence of restoration, coral reefs in Florida and Puerto Rico will continue to decline, further increasing the risk of flooding. But the reports find reason for hope: Coral reef restoration across Florida and Puerto Rico could prevent the loss of more than $270 million annually from flooding.

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The complex, three-dimensional reefs built by corals over hundreds to thousands of years provide invaluable ecosystem services to society—contributing billions of dollars per year to the global economy through shoreline protection, tourism, and habitat for biodiversity and fisheries. The growth of these reefs is increasingly threatened by climate change and other disturbances, which have caused global-scale reductions in reef growth and increases in reef erosion. Despite unprecedented declines in reef-building corals in recent decades, new research by Dr. Lauren Toth and colleagues shows that real-world coral restoration efforts could bring coral reef growth back to historic levels—as high as they were 7,000 years ago. Listen to audio-described version.

Maintaining Valuable Natural Infrastructure

Measures to protect and restore these critical ecosystems can not only safeguard coastal communities, but also bolster their resilience against future climate-related challenges.

Efforts to restore and protect coral reefs have gained momentum in recent years. Research conducted by the USGS is helping to guide these efforts and provide specific objectives that will be most effective at reducing the effects of coastal hazards induced by a changing climate. These restoration projects, based on scientific findings and risk assessments, aim to rebuild and rehabilitate damaged or degraded reefs, allowing them to regain their protective functions while simultaneously supporting tourism, fisheries, and marine biodiversity.  

The USGS provides a wide range of coastal expertise to assess risks, understand impacts, and monitor changes. As coastal habitats, including coral reefs, face increasing threats from climate change, pollution, and human activities, these studies provide guidance and tools to evaluate and reduce risks while improving resilience for coastal communities.

USGS scientists are working with a wide range of partners to better understand and quantify the role that critical natural infrastructure provides. Not only in south Florida, but across the nation where coastal communities depend on coral reefs or other natural buffers for the protection and ecosystems services they provide.