Cement tiles with two percent sodium carbonate increase water alkalinity around newly settled coral larvae. In experiments at the University of Miami, the survival rate of the reef-building coral Orbicella faveolata rose from 12 to 52 percent, more than four times the baseline. The method, published April 20, 2026 in Communications Earth and Environment, could eliminate one of the largest bottlenecks in global coral restoration.
The Silent Death of Reefs
Coral reefs cover less than one percent of the seafloor but house approximately one quarter of all marine species and provide millions of people on tropical coasts protection from storm surge. Since the 1950s, Earth has lost roughly half its reefs. In the Atlantic, losses since the 1980s amount to approximately 80 percent according to NOAA, caused by coral disease and repeated bleaching events from rising ocean temperatures. At 1.5 degrees of global warming, IPCC projections warn that 70 to 90 percent of all reefs face disappearance.
The core restoration problem lies not with adult corals but earlier in the lifecycle: coral larvae swim freely in water and must settle on suitable substrate. Under natural conditions, fewer than 15 percent survive this phase. Even in well-controlled breeding programs, this transition remained barely controllable. Without improvement at this point, even ambitious restoration programs cannot keep pace with reef loss.
The Sodium Carbonate Solution
Melissa Ruszczyk, then at the Rosenstiel School of Marine, Atmospheric, and Earth Science at the University of Miami, tested various cement tiles as settlement substrate for the reef-building coral Orbicella faveolata with marine biology professors Chris Langdon and Andrew Baker and physics professor Vivek Prakash. Over five months they varied shape and sodium carbonate content: none, one percent, or two percent, flat or textured. Cooperating partner was the international conservation organization SECORE International, specializing in coral restoration.
Results were unambiguous: flat tiles with two percent sodium carbonate performed far best. The mechanism is direct: the material releases carbonate ions when exposed to seawater, elevates pH in the immediate vicinity, and creates an alkaline microenvironment. Coral larvae require a specific pH range for skeleton formation, increasingly impaired by ocean acidification from CO2 inputs. The sodium carbonate tiles counteract this effect locally. The team notes its own limitation: the study includes only one coral species. Whether the method works similarly with other reef builders requires additional testing.
Comparable Restoration Approaches
Coral restoration is an active research field with several parallel approaches. Coral Vita, based in Grand Bahama, employs accelerated fragmentation in land farms claimed to enable coral growth 50 times faster than in nature. The Australian Institute of Marine Science (AIMS) breeds heat-tolerant coral strains that grow more resilient through repeated selection. Australia's Coral Nurture Program focuses on directly planting fragments on degraded reef areas.
None of these approaches directly improves survival rates during the critical early settlement phase when larvae must transition from free-swimming to firmly settled. The sodium carbonate tiles target exactly this point. They are relatively inexpensive to manufacture, deployable without high-tech infrastructure, and transferable to various reef regions according to researchers.
From American Samoa to the Coral Triangle: Open Questions
A parallel project shows how scaling could work. The University of Hawaii coordinates with the University of Miami, American Samoa Community College, and American Samoa's Department of Marine Resources with NOAA, the US coastal agency, funding 4.6 million dollars. American Samoa was chosen because its reefs rank among the healthiest and heat-tolerant in US waters and host the world's longest continuously monitored coral transect. Three doctoral fellowships go to applicants from American Samoa.
The actual test occurs elsewhere. The so-called Coral Triangle, encompassing Indonesia, the Philippines, Papua New Guinea, the Solomon Islands, Malaysia and East Timor, harbors 76 percent of all known coral species worldwide according to the WWF. It is simultaneously the region where state conservation budgets are tightest and reefs suffer most from overfishing, coastal development, and climate change. Most coastal residents there depend directly on reef ecosystems for food and fishing.
For the sodium carbonate method to arrive there, field trials would first need to demonstrate efficacy under variable water temperatures and wave conditions and with additional coral species. Then come questions of mass manufacturing, logistics, and financing. Miami researchers proved the biological problem solvable. Whether it is also solvable at large scale and in resource-limited regions remains primarily a political question.