Abstract
Coastal cities are becoming increasingly vulnerable to the worsening effects of climate change, including severe storm events, rising sea levels, flooding, and coastal erosion. Traditional shoreline defenses using gray (cement-based) infrastructure, such as submerged breakwaters, bulkheads, and seawalls result in the removal of natural habitat and require ongoing maintenance. In response, hybrid approaches that integrate green (nature-based) solutions, such as coral reefs and mangroves, with gray infrastructure (green-gray infrastructure), are emerging as optimal solutions by providing long-term benefits of ecosystem resilience and structural durability. However, climate-induced warming of the oceans has dramatically impacted thenature-based component, particularly coral reefs, which have suffered frequent episodes of “bleaching” in recent years. Consequently, there is a pressing need for a novel gray-green hybrid approach that offers both coastal protection and biological resilience. Here, the term “X-reef” is introduced to refer to a next-generation hybrid reef that combines green and gray infrastructure to protect coastlines from wave impacts, flooding, and erosion, while also incorporating novel interventions to enhance the resilience of the biological component to withstand future environmental changes. As a major case study, we describe the X-REEFS project funded by the U.S. Department of Defense (DARPA) in southeast Florida that is designing and testing a novel hybrid reef to be both wave-attenuating and biologically resilient with enhanced heat- and disease-resistant corals. The X-REEFS project scales up the benefits of existing state-of-the-art infrastructure and develops innovations in structures, materials, ecology, and biology to protect civilian and Department of Defense (DoD) infrastructure. We describe how the project is developing the first X-reef in Florida through efforts in five major areas: shoreline protection,field deployments and monitoring, physical and environmental enhancements, biomass production, and biological enhancements.