Sixty engineered, porous concrete structures now sit on the seafloor south of Kalaeloa Harbor, each one designed to grow live coral and blunt the ocean's force before it reaches Oahu's coastal highways. The Hawaiʻi Department of Transportation launched the deployment as the first large-scale ocean demonstration of what researchers call a hybrid reef, a living breakwater meant to reduce wave energy, strengthen shorelines and improve coastal resilience as sea levels keep climbing.
The project, first reported by Maui Now, follows four years of research and development led by the Rapid Resilient Reefs for Coastal Defense consortium, or R3D, which is headed by the University of Hawaiʻi's Applied Research Laboratory and its School of Ocean and Earth Science and Technology. The structures were manufactured in Hawaiʻi and combine an engineered concrete base built to dissipate wave energy while letting water flow through, with living coral fragments attached to accelerate long-term growth. HDOT Director Edwin Sniffen said the project is intended to build a resilient, self-sustaining ecosystem, and that success at Kalaeloa could provide a model for protecting vulnerable coastlines throughout Hawaiʻi and beyond, according to the same report.
A Defense Department Bet on Living Infrastructure
The funding trail behind Kalaeloa runs through the Pentagon. In June 2022, DARPA awarded up to $25 million over five years to the UH-led R3D consortium to design self-healing coastal protection systems, according to UH News. DARPA created the broader Reefense program after identifying more than 1,700 Department of Defense-managed coastal installations worldwide facing rising threats from sea level rise, wave-induced flooding and severe storms, per DARPA. Hawaiʻi's team was one of three regional efforts funded under Reefense that year, alongside Rutgers University's work on Gulf Coast oyster reefs and the University of Miami's work on Atlantic coral reefs, DARPA noted.
DARPA funded the hybrid reef structures themselves, and ownership will transfer to HDOT, according to Maui Now's reporting. Catherine Campbell said Reefense combines materials science with adaptive biology to protect vital infrastructure and personnel, per the same account. The engineering emphasis reflects a known weakness in conventional hard seawalls, which suppress waves immediately but frequently accelerate beach erosion and lack long-term adaptiveness, according to DARPA.
Why Highways Need a Living Shield
The stakes for Hawaiʻi's roads are steep. A 2018 state assessment reported by Honolulu Civil Beat estimated that adapting and defending Hawaiʻi's public highways against rising seas and coastal erosion will cost roughly $15 billion statewide, with corridors like Kamehameha Highway on Oahu already suffering regular shoreline loss and seawater inundation. Natural coral reefs, when healthy, can absorb up to 97 percent of incoming wave energy, effectively acting as seawalls, according to research published by UH Noelo Magazine.
That natural buffer is disappearing fast. Marine research cited by UH Noelo Magazine shows more than half of the world's coral reefs have died over the past 70 years, with projections suggesting up to 90 percent could perish within a century absent intervention. Reefs cover under one percent of the ocean floor yet harbor a quarter of all marine species, the same research notes, underscoring what is lost when reefs vanish.
Engineering the Reef, Piece by Piece
According to Maui Now's account of the Kalaeloa project, the hybrid reef aims to reduce coastal erosion, wave damage and storm surge while enhancing marine habitat, and its 60 structures rely on specially developed biomaterials that repel competing algae and accelerate coral growth. The project site itself is a degraded stretch of hard rock bottom south of Kalaeloa Harbor; coral fragments already present there are being removed and preserved on growing tables nearby before crews install the reef structures and attach live coral fragments to them, per the same reporting.
Some of the underlying components were tested well before deployment. Wave-flume tests found that model breakwaters reduced incoming wave energy by more than 80 percent and remained stable during extreme conditions, Maui Now reported. The Hawaiʻi Institute of Marine Biology developed 3D-printed ceramic coral habitat modules with spiral-shaped shelters, and helix-shaped recesses in those modules yielded an 80-fold increase in baby coral settlement and up to a 50-fold increase in coral survival rates compared with flat surfaces, according to the same account. UCSD researchers separately developed materials that reduce algae competition while letting coral grow on the structures, and UCSD-SIO researchers recorded the sounds of healthy reefs for broadcast near the living breakwater, aiming to draw algae-grazing fish to the site.
Deployment itself was engineered to limit disturbance. Makai Ocean Engineering built a shallow-water catamaran that eliminates the need for heavy crane barges, and the reef structures are being anchored using a rotary micropiling system that reduces both the anchoring footprint and sound pollution compared with traditional pile drivers, per Maui Now.
Regulatory Review and Community Input
Before any submerged construction began, DARPA prepared a federal Environmental Assessment under the National Environmental Policy Act, while HDOT conducted a parallel state environmental review under Hawaii Revised Statutes Chapter 343, according to the Applied Research Laboratory at the University of Hawaiʻi. The federal assessment underwent a public comment period in August 2025. Project researchers also conducted outreach across Oahu through 2024 and 2025, presenting plans to the Kapolei Neighborhood Board, the Kapolei Hawaiian Civic Club and the Kalaeloa Heritage and Legacy Foundation, along with local fishers working groups and cultural practitioners, per the same source.
Ben Jones said Kalaeloa will become a living laboratory for evaluating nature-based coastal engineering, Maui Now reported. Findings from the site will be shared with regulators, engineers and coastal managers, and are expected to inform future shoreline protection projects in Hawaiʻi and elsewhere, according to the same reporting. A newly formed Kalaeloa Hybrid Reef Monitoring Hui, made up of researchers, agency representatives, community organizations and cultural practitioners, will guide long-term monitoring of the reef's environmental, engineering and cultural impacts as the project team conducts continued scientific monitoring.
Who Pays to Keep It Running
Ongoing costs now shift to the state. Hawaiʻi's Green Fee, enacted through Senate Bill 1396, or Act 96, in July 2025, created a dedicated climate resilience fund financed by a 0.75 percent increase in the state's transient accommodation tax on visitors, making Hawaiʻi the first state in the nation with a dedicated visitor fee for climate and environmental resilience projects, Hoodline previously reported. That fund is now covering the Kalaeloa reef's first year of monitoring and maintenance, per Maui Now's reporting. Governor Josh Green said the Green Fee invests in innovative solutions that protect Hawaiʻi's people, natural resources and economy, according to the same account.
The project has also become a training ground for the state's next generation of transportation workers. During HDOT's summer 2025 internship program, participants presented a project titled Under the Sea, Under Construction: A Reef's New Beginnings, examining the Kalaeloa Reef Laboratory's role in protecting state infrastructure, as Hoodline detailed in its coverage of the 12-week internship program that engaged more than 120 high school and graduate students across HDOT divisions.
Whether the living breakwater performs as well against a real hurricane as it did in wave-flume tests, and whether the transplanted coral can survive as ocean temperatures keep rising, remain open questions the monitoring hui will be watching in the years ahead.
