Soterium Earth · Ocean Restoration
Biorock Accretion
Growing living rock on steel with a gentle electric current, and what the evidence really says.
Run a small, safe electric current through a steel frame in seawater, and something remarkable happens: a layer of limestone begins to grow on the metal, built from minerals already dissolved in the sea. It is the same material that makes up shells and coral skeletons, and it keeps growing for as long as the power stays on.
The process is called mineral accretion, and Biorock is its best-known form. Its supporters see it as a way to build living reefs and self-repairing sea walls. Recent independent studies are more cautious. This page covers how it works, what the evidence actually shows, and how Soterium Earth would use it.
Early-stage concept. Biorock is one of the supporting technologies of Project Halogrove. We would only use it alongside untreated controls, and only where the evidence supports it.
- Developed
- 1976, by architect Wolf Hilbertz
- Method
- Low-voltage direct current through steel in seawater
- Main mineral
- Aragonite, a hard form of limestone
- Also called
- Mineral accretion technology (MAT), electric reefs
- Evidence
- Strong for building material; weak or negative for coral health
The chemistry
How it works
A steel frame becomes the negative electrode (cathode), and a separate metal piece becomes the positive one (anode). A low-voltage direct current flows between them through the seawater, splitting water at each end.
Rock grows
Splitting water here releases hydrogen and hydroxide. The hydroxide makes the water right at the surface more alkaline, and calcium and magnesium minerals settle out of the seawater onto the steel.
Oxygen and acid
The other end releases oxygen and a little acid. Above about 1.36 volts it can also make small amounts of chlorine, which proponents say seawater quickly neutralizes.
Slow is strong
Low current builds hard aragonite. High current builds soft, flaky brucite instead, which slowly converts. Growth of about 1–2 cm a year gives the strongest rock, and lower voltages use electricity more efficiently.
Origins
From building material to reef
Wolf Hilbertz, an architect, saw seawater minerals as a building resource in 1976: a way to grow construction material in the sea instead of quarrying it. Its developers report the resulting rock at roughly three times the strength of ordinary concrete, and it can regrow where damaged as long as power flows.
Working with marine scientist Thomas Goreau and the Global Coral Reef Alliance, Hilbertz turned the process toward reef restoration. One of their best-known projects began in 2000 at Pemuteran, Bali: within a year, 28 structures stretched about 300 meters across a community marine protected area, with local hotels donating the electricity and fishers, divers and welders helping build them.
The honest picture
What the evidence says
Much of the early evidence for Biorock comes from its developers, and some of it is unpublished. Recent independent studies tell a more mixed story.
| Study | What it found |
|---|---|
| Developers' reports | Coral growth 2–6 times faster than controls, and far better survival during bleaching. Much of this has not been independently confirmed. |
| Great Barrier Reef, Australia (2023) | The current grew plenty of mineral on the steel, but did nothing for the survival or growth of transplanted corals. The authors saw value in it for new hard surfaces and rubble stabilization. |
| Kenya (PLoS One, 2024) | During a marine heatwave, corals on powered structures bleached more severely. After a year, unpowered controls had 34 new coral recruits; powered structures had none. The authors noted it does help prevent the steel from corroding. |
| Lombok, Indonesia (2025) | Corals grew faster, but one species produced about 40% fewer larvae, and skeletons were less dense and more fragile. |
| Miami lab study (Coral Reefs, 2026) | Very small coral fragments within 5 mm of the cathode calcified about 43% faster. Taller fragments gained nothing beyond the mineral growing on its own. |
The pattern: mineral accretion reliably grows rock and protects steel. Whether it makes corals healthier is, at best, unproven, and fast growth can come at the cost of reproduction and strength.
Our use for it
Where it fits in Project Halogrove
We see Biorock first as an engineering tool, not a coral booster. In Halogrove, its job is to armor steel in the sea: the legs of retired platforms used as rig reefs, and the anchors of floating mangrove platforms.
Growing a limestone skin on that steel protects it from corrosion and can regrow where damaged. Power could come from the platforms' own wave energy, so the system feeds itself. The living reef would grow on that rock the natural way, judged by its own health, not by how fast the current makes it grow.
- Best-supported uses
- Growing hard substrate
- Stabilizing rubble
- Protecting steel from corrosion
- Not proven for
- Coral health, heat resilience or recruitment
Our approach
How Soterium Earth would test it
Always with controls
Every powered structure gets an identical unpowered twin nearby, so any effect can be measured, not assumed.
Measure more than growth
Track reproduction, skeleton density, bleaching, new recruits and biodiversity, not just how fast things grow.
Low current, hard rock
Run at low voltage for strong aragonite and efficient power use.
Power from the site
Use wave or solar energy generated on site, so the system adds no fossil fuel load.
Know when to switch off
If powered structures do worse, as in the Kenya study, turn the power off. The rock already grown stays.
Publish everything
Share results, positive or negative, so others can learn from them.
Still to solve
Open questions
Corals or just rock?
Why do some studies show faster coral growth and others show harm? Distance from the cathode, current and species may all matter.
Life on the anode side
How do the oxygen, acid and trace chlorine affect nearby animals over years, not months?
Scale and power
How much energy does it take to armor a full platform leg, and can wave power supply it reliably through storms?
After the power stops
How long does the grown rock last once the current is gone, and does it keep protecting the steel?
Keep exploring
Related pages
Sources
- Marine electrolysis for building materials and environmental restoration (Goreau, InTech)
- Pemuteran Coral Reef Restoration Project (Global Coral Reef Alliance)
- Lessons learned implementing mineral accretion and coral gardening at Agincourt Reef (Ecological Management & Restoration, 2023)
- Negative effects by mineral accretion technique on the heat resilience, growth and recruitment of corals (Knoester et al., PLoS One, 2024)
- The hidden trade-off of growing corals quickly (Blue Corner, on Taylor 2025)
- Electrochemically induced alkalinity enhancement increases coral growth rates in the local microenvironment (Kiel et al., Coral Reefs, 2026)