The Value Of US Coral Reefs For Flood Risk Reduction
Coral reefs have been called the “rainforests of the sea” due to their high levels of biodiversity and productivity. Reefs are highly productive marine ecosystems that serve as a habitat for a great diversity of marine animals and plants. Reefs are also highly beneficial to humans due to the ecosystem services they provide.
Ecosystem Services Provided by Coral Reefs
Although coral reefs occupy less than 0.1% of the world’s ocean area, they support approximately 250 000 marine fauna and flora species, with a million species more indirectly associated with reefs. Each of these organisms in turn play an important role in the reef ecosystem. By supporting such a high variety of organisms, coral reefs assist with maintaining a functional ecological balance in marine ecosystems.
Corals also assist with nutrient cycling and carbon fixation. There exists a symbiotic relationship between coral polyps and photosynthetic algae called zooxanthellae that lives within the corals. The zooxanthellae feed on nitrogen waste produced by coral polyps, and provides oxygen as well as organic matter used by the corals. This process helps in carbon fixation by transforming inorganic carbon into organic carbon. Coral reefs therefore assist with regulating carbon dioxide levels in oceans.
Corals also form the backbone of regional economies, as coral reef-based tourism and the associated recreational activities provide additional sources of income to coastal communities. Due to their high levels of biodiversity, coral reefs also support the global fishing industry. It is estimated that at least 500 million people rely on coral reefs for their livelihoods.
Coral Reefs and Coastal Protection
Stony corals, the coral species that are predominantly involved in reef-building in coastal areas, serve as natural marine barriers that dissipate wave energy. This is especially important during hurricanes, storms and tidal surges, when beaches and coastal communities are protected from flooding, loss of infrastructure and erosion. Coral reefs also help stabilize mangroves and seagrass beds, which could be uprooted and destroyed by large waves.
Economic Value of Coral Reefs in the United States
In 2019, the United States Geological Survey, the University of California and the National Oceanic and Atmospheric Administration published a detailed study into the economic value of coral reefs in the United States. This study estimated that coral reefs in U.S. waters from Florida, the Caribbean, Hawaii and Guam, provide flood and coastal protection to more than 18 000 people, contributing an estimated value of $1.8 billion worth of coastal infrastructure and economic activity every year. Through mitigating the direct flood potential and subsequent risk of damage to infrastructure coral reefs provide another $800 million annually, and further help to avoid additional cost of life and livelihoods up to an estimated $1 billion. Although most people value reefs for their beauty, studies like this one that assigns an economic value to reefs assist with mobilizing resources needed for reef conservation.
Acting as Wave Breaks
Reefs behave like underwater breakwaters, by “breaking” waves and dissipating the energy offshore, away from the coast. As tropical storms are increasing and causing severe economic damage (having caused more than $265 billion of damage in the United States in 2017) governments are turning to man-made defenses, such as sea walls, however these solutions can destroy marine ecosystems and habitats. Coral reefs are able to not only protect shorelines naturally, but also promote a healthy fishing industry and provide recreational activities and eco-tourism ventures.
The study further found that losing only one meter of reef height would cause 100-year flooding zones to increase by 23%, which will impact 53 000 more people (a 62% increase) and 90% more property, increasing damages by $5.3 billion.
It is estimated that the United States has 200 miles of high-value coral reefs, worth $1.6 million per mile annually for flood protection alone. Most of these high-value reefs are found in the coastal waters of Florida and Hawaii.
How to Estimate the Value of Coral Reefs
Researchers that participated in the study combined computer models of storm events and waves with engineering, ecological, mapping, social and economic tools to create detailed estimates of the value of coral reef defenses along U.S coastlines. Flood risk and reef benefits were assessed from reefs along the coasts of Hawaii, Florida, Guam, American Samoa, Puerto Rico, the U.S. Virgin Islands and the Commonwealth of the Northern Mariana Islands.
The aim of the study was to produce information and economic estimates to be used by a wide variety of coastal managers working on flood mitigation, coastal defense, transportation, hurricane response and recovery. The study also calculated how much critical infrastructure is protected from coastal flooding due to the presence of the coral reef. Computer models were used to forecast flood damages with and without coral reefs along the shoreline to calculate these values. The same approach can also be applied to other ecosystems, and allows assessing the impacts of future changes to oceanic conditions due to climate change, such as increased storm frequency and sea level rise.
Although sea level rise is presented as an imminent threat to coastal communities and economies, the loss of coral reefs will have similar impacts in a much shorter time frame. Coral reefs are degrading world-wide, however they can still be recovered if adequate resources are invested in their management and restoration.
The study done by the U.S. Geological Survey quantifies the critical role that coral reefs play in flood mitigation, providing the evidence needed to invest in hazard management and disaster recovery. Some of the data produced by the study is already being used by the Federal Emergency Management Agency and the Nature Conservancy to inform reef restoration.
Coral Reef Restoration
New guidelines for coral reef restoration were published in Frontiers in Marine Science, aiming to optimize restoration efforts to benefit the ecosystem and the coastal communities. The study analyzed over 30 000 reef profiles across the U.S. and numerically designed reef restorations to be feasible and operational ecologically, while having a beneficial impact on coastal flooding. Such studies can assist in preventing future flood damage to coastal communities and also prevent continuous coral degradation.