Recent major hurricanes in the Caribbean have emphasized the vulnerability of coastal communities to wave energy from extreme events. Episodic extreme wave energy can not only damage corals (e.g., breakage, overturning) and reef structure (e.g., fractures to reef framework), but also can impact coastal infrastructure near degraded reefs. As coral populations have declined and reef structural complexity has degraded, efforts to implementation and scale-up coral restorations have gained in momentum. Many coral restoration efforts have focused on ecological goals, but few to date have also included the quantitative bio-physical and coastal engineering approaches needed for coastal hazard risk reduction. Successful efforts towards this goal will not only address the normal range of abiotic conditions (e.g., hydrodynamics, temperature), but also need to realistically accommodate some extent of extreme events, particularly in the context of a changing climate. A grey-green infrastructure approach may also need to be considered for implementation. We address potential applications of fluid mechanics, hydrodynamics, and multi-dimensional hydrodynamic models. Here, we provide a decision support framework to increase the potential for successful coral restorations at scales large enough to reduce risk from coastal hazards. Finally, we recommend future directions for scaling-up coral restoration efforts for coastal resilience.

Coral reefs naturally protect coasts from erosion and flooding by attenuating wave energy and supplying sediment to the adjacent beaches. Declines in reef condition coupled with increasing rates of global sea level rise are jeopardizing communities and coastal infrastructure. The typical hard engineering solution to this problem is to construct breakwaters or groins to protect high value shorelines, even in places where shallow reef crests occur. Softer solutions such as coral restoration may offer a cost-effective alternative to traditional engineered solutions in some places. It should be feasible to structurally restore degraded reefs using both biological and physical techniques including the use of structural materials. However, few reef restoration projects have been designed with coastal protection as a primary objective and guidelines are lacking. Here we discuss the process of designing a low crested breakwater structure to restore the wave breaking properties of a degraded reef crest in Grenada. Structures were designed to withstand hurricane wave forces, have a minimum 30 year lifespan, and promote coralline algae and coral growth. A total of 30 meters of pilot structures were constructed in 2015 and installed on a high energy back reef environment using local materials, community labour, and a specially built shallow water barge. Monitoring results of the pilot structures suggest they perform similar to traditional submerged breakwaters but have significantly greater ecological benefits including the potential to enhance natural reef accretionary processes.

Coral reefs play an important role in coastal protection and reduction of risks derived from climate events. Reefs dissipate wave energy, reduce storm surge and maintain shoreline elevation, protecting coasts from erosion and flooding. Several ecological, geological, and oceanographic factors contribute to the coastal protection capacity of reefs. Nevertheless, the combined impacts of climate change and some anthropogenic factors reduce this capacity. Coral reef restoration can be employed to restore key ecosystem services, such as coastal protection, especially if the physical structure of the reef has been degraded and can serve as a risk reduction solution when it is combined with a series of management approaches that can boost coastal protection values. This type of restoration can meet conservation, resource management and disaster risk reduction objectives simultaneously, and provide multiple socio-economic benefits to coastal communities. A series of recommendations for global application based on lessons learned from Mexico are presented to assess when, where, and how to apply reef restoration for risk reduction.

Long-term coral reef degradation leads to a significant coral loss and to a net decline in reef accretion, resulting in a permanent state of mediocrity. Such altered reefs have evolved into de facto novel ecosystems characterized by declining biodiversity, impaired ecological functions and services, and reef flattening, reducing its wave buffering and essential fish habitat roles. Cross-reef wave power reduction was preliminarily modeled to quantify restored reef performance and to analyze the effectiveness of idealized reef configurations in dissipating wave energy and reducing the wave power reaching the nearshore region. Preliminary analyses suggest that under highly flattened conditions wave energy and height attenuation can barely reach 14% and 3%, respectively, across reefs with a sparse fringe of Acropora palmata. But, coastal reefs with higher physical structuration can reduce more than 80% of wave power. Optimal reef centroid positioning has important implications for the design of coral reef restoration projects. If the goal is to optimize the degree of coastal protection provided by a restored reef, without seabed modification (e.g. excluding a submerged structure that decreases effective water depth), then the ideal restoration location may not be at the existing reef crest, but closer to shore, highlighting the importance of shallow coastal reefs rehabilitation. The integration of long-term projections generated by stochastic demographic models for A. palmata, A. cervicornis, and Orbicella annularis parameterized with long-term data under present environmental conditions in Puerto Rico suggests that these species might face a high extinction risk under projected climate change-related stress. Recurrent coral mortality events associated to multiple stressors result in negative population growth rates (λ) and in a threat to the long-term success of reef rehabilitation. Regardless of small spatial scale success, reef rehabilitation strategies can have very limited impacts on wave attenuation and enhancing coastal resilience unless a significant increase in the magnitude, spatial and temporal scale of interventions is achieved, and unless sources of mortality are curtailed. The integrated role of wave numerical models and demographic models is discussed as a tool to address the simulated impacts of multiple spatial designs of reef rehabilitation interventions.

Healthy coral reefs provide coastal protection and natural defenses against climatic extremes. Coral reefs provide up to $30 billion to the global economy, with $9 billion made up by the coastal protection benefits they afford. Recent numerical modelling studies have shown that reefs can reduce wave energy by 97% and wave height by 84%, limiting physical impacts to the shoreline and reducing flooding. However, as reefs decline due to disease, pollution, increased ocean temperature, and acidification, coral propagation and reef restoration have become common intervention tools to mitigate impacts and recover lost services. As restoration efforts have now expanded to ecologically meaningful scales, it is important to ascertain whether restored reefs can offer meaningful coastal protection. In this project, we validate large-scale hydrodynamic models using experiments conducted at the University of Miami’s SUSTAIN wave tank using realistic coral models and provide field validation tests using floating wave sensors deployed over healthy and degraded Florida reefs. Through these experiments, we address scale and data gaps and potential parameters of importance, such as reef height, coral density, coral community structure, and coral spatial arrangement, which may influence wave height and energy. The information gathered will help guide future reef restoration efforts aimed at providing coastal protection benefits an enhancing coastal resilience.

Near shore coral reef ecosystems provide coastal protection from storm surge and flooding, and in a changing climate with predicted increases in storm frequency and intensity, as well as rising sea levels, this protection of coastal infrastructure becomes more critical. Increased storm frequency and intensity raises the ecosystem value of these natural structures, while simultaneously increasing the threat of disturbance to them. To track changes in ecosystems services, post-disturbance assessment and triage has become a crucial component of long term restoration monitoring efforts and their success. In 2017, two category 5 hurricanes hit the islands of Puerto Rico within 2 weeks. Following that disturbance, in 2018, a large scale impact assessment was launched by FEMA with the support of NOAA's National Marine Fisheries Service (NMFS) Protected Resources, the NMFS Restoration Center and the National Centers for Coastal Ocean Science (NCCOS) to facilitate the National Disaster Recovery Framework Natural and Cultural Resources Recovery Support Function. In 39 field days, the field team visited 153 sites and assessed 80,000 corals for damage, covering an area of 414,354 m2 of coral habitat. Overall, 11% of Puerto Rico’s coral reefs sustained damage with the ESA listed species Dendrogyra cylindrus, Acropora palmata, Orbicella annularis, and Acropora cervicornis sustaining the majority of the damage. This information was used to direct triage efforts and identify 12 potential areas covering 465 km2 for large scale restoration and long term monitoring. This effort is one of the first of its kind to formally recognize corals reefs as natural infrastructure in need of federal support in the wake of disturbance. These efforts will not only increase the populations of threatened coral species in Puerto Rico, but will bolster the coastal protection ecosystem services by restoring the natural infrastructure these corals provide.

Reefs and associated ecosystems serve as barriers, buffers, and breakwaters from rising seas, swell, and storm surge. Until recently, it was not possible to put a value on the flood protection benefits from these nature based solutions. This is changing rapidly, however, and recent studies are showing surprising results. Mangroves can reduce annual flood damages to people and property by 20% percent. Without coral reefs damages from storms would double; they avert billions of dollars in flood in flood damages every year. We use insurance industry-based models to show the restoration of reefs and wetlands is cost-effective as well for reducing impacts from storms, particularly when compared to built or gray infrastructure such as seawalls or dikes. This talk will summarize high-level findings from the latest research on the ecology, engineering, and economics of nature based defenses and identify where these can inform innovative tools in insurance and policy.