Biorock, also known as Seacrete or Seament, is a trademark name used by Biorock, Inc. to refer to the substance formed by electro-accumulation of minerals dissolved in seawater. Prof. Wolf Hilbertz developed the process and patented it in 1979. The building process, popularly called accretion, is not to be confused with Biorock sewage treatment. The biorock building process grows cement-like engineering structures and marine ecosystems, often for mariculture of corals, oysters, clams, lobsters and fish in salt water. It works by passing a small electrical current through electrodes in the water. The structure grows more or less without limit as long as current flows.
In an attempt to slow the damage done to the world’s coral, artificial reefs have been built since the 1950s out of materials ranging from concrete blocks to discarded tires. However, most of these plans have failed to provide a new coral habitat. Most notoriously, the attempt using tires off the shore of Fort Lauderdale has become an environmental disaster. There have been some successes with artificial reefs, but most remain relatively barren compared with natural reefs. The one notable exception is the work of architect/marine scientist Prof. Wolf Hilbertz (born 1938, died 2007) and marine biologist Dr. Thomas J. Goreau (born 1950).
Biorock technology arose from experiments in the 1970s when Hilbertz was studying how seashells and reefs grow, by passing electrical currents through salt water. In 1974, he found that as the salt water electrolyzes, calcium carbonate (aragonite) combines with magnesium, chloride and hydroxyl ions to slowly form around the cathode, eventually coating the electrode with a material similar in composition to complex magnesium oxychloride cements and as strong as concrete. Over time cathodic protection replaces the negative chloride (Cl-)ion with dissolved bicarbonate (HCO3-) to harden the coating to a hydromagnesite-aragonite mixture with gaseous oxygen being evolved through the porous structure. Later experiments showed that the coatings can thicken at the rate of 5 cm per year. As long as current flows, the structure continues to get larger and stronger. It can also heal itself if damaged, making it particularly useful as a replacement for concrete in hard-to-access locations. High levels of dissolved oxygen make it particularly attractive to marine organisms, particularly fin fish.
Hilbertz originally called his invention, on which he had several patents, underwater mineral accretion or accretion for short. The term biorock wasn't coined until later. Hilbertz’s original plan was to use this technology to grow low-cost structures in the ocean for developing countries. He also envisioned accreting large aquadynamic OTEC ocean thermal energy conversion plants, both for generating power and for producing hydrogen, ammonia, and magnesium hydroxide. This appeared to result in a building process largely independent of land-based resources.
His focus shifted to coral reefs after meeting Dr. Thomas J. Goreau in the 1980s. They formed a long-standing partnership, with Goreau continuing work on biorock technologies and coral reef restoration after Hilbertz' death in 2007. Because the biorock process uses such simple materials, electrode forms can be constructed in a variety of shapes to mimic natural reefs. Since the combined hydrated magnesium oxychloride, brucite (magnesium hydroxide) - later hydromagnesite (magnesium chlorocarbonate) and aragonite (calcium carbonate) coating that forms is so similar to natural reef substrate, corals take to biorock reefs very readily. Countless projects over the years have demonstrated that coral thrive on the electrified and oxygenated reef environment. One prominent example was in the Maldives during the 1998 warming, during which fewer than 5% of the natural reef corals survived. On biorock reefs in the area, 80% of corals not only survived, they flourished.
With others, Hilbertz and Goreau made two expeditions to the Saya de Malha bank in 1997 and 2002. Using Biorock technology, they attempted to grow an artificial island around steel structures that were anchored to the sea floor. As "Seacrete" the process was substantially publicised in a 1992 book of futurology, The Millennial Project. The author, Marshall Savage, reiterated Hilbertz' earlier proposal that the conductive metal magnesium be extracted from ocean water, and that the process use electricity from ocean thermal energy conversion. In 2012, both Dr. Goreau and Robert K. Trench, writing together with Goreau, published works on how Biorock technologies could be implemented for generating building materials as well as restoring damaged ecosystems. 
Applying a low voltage electrical current (completely safe for swimmers and marine life) to a submerged conductive structure causes dissolved minerals in seawater, principally calcium, magnesium and bicarbonate to precipitate and adhere to that structure. The result is a composite of brucite hydromagnesite and limestone with mechanical strength similar to concrete. Derived from seawater, this material is similar to the composition of natural coral reefs and tropical sand beaches.
Biorock structures can be built in any size or shape depending only on the physical makeup of the sea bottom, wave, current energies and construction materials. They are well suited for remote, third world sites where exotic building materials, construction equipment and highly skilled labor are non-existent.
Constructing a new reef
To build a biorock reef, a welded, electrically conductive frame, often made from construction grade rebar or wire mesh, is submerged and anchored to the sea bottom. A low voltage direct current is applied using an anode. This initiates an electrolytic reaction causing mineral crystals naturally found in seawater, mainly calcium carbonate and magnesium hydroxide, to grow on the structure.
Within days, the structure takes on a whitish hue as it becomes encrusted with precipitated minerals adding rigidity and strength. Electrical fields, plus the shade and protection offered by the metal/limestone frame, attract a wide range of colonizing marine life including fish, crabs, clams, octopus, lobster, and sea urchins.
Once the reef structure is in place and minerals begin to coat the surface, the next phase of reef construction begins. Divers transplant coral fragments from other reefs, attaching them to the ark’s frame. Immediately, these coral pieces begin to bond to the accreted mineral substrate and because of evolved oxygen and the electrochemically facilitated accretion of dissolved ions, such as bicarbonate - start to grow—typically three to five times faster than normal. Soon the reef takes on the appearance and utility of a natural reef ecosystem rather than a man-made one.
Electrolysis of biorock reefs enhances coral growth, reproduction and ability to resist environmental stress. Coral species typically found on healthy reefs gain a major advantage over the weedy organisms that often overgrow them on reefs stressed by eutrophication. In tests where the electrical current is interrupted, mineral accretion stops and weeds begin to cover the corals. But, if the current is maintained, coral reef habitats can often be restored even in areas where water quality would prevent their recovery by any other method.
Biorock reefs grow rapidly and strengthen as they age. They thus have great potential for many applications, such as making breakwaters. If waves or colliding ships cause damage, renewed accretion makes them, to an extent, self-repairing. Unlike some other types of artificial reefs made from cars or tires, biorock reefs don't leach harmful pollutants into the sea.
Biorock accelerates growth on coral reefs by as much as fivefold and increases coral survival. Biorock can enable coral growth and regrowth even in the presence of environmental stress such as thermal pollution, i.e. increasing water temperatures. When mixed with construction aggregates, it can build components on the sea floor or on land. Biorock represents the only known method that can sustain and grow natural coral species using only basic conducting elements, typically of a common metal such as steel.
Biorock samples range in compressive strength from 3720 to 5350 lbf/in² (26 to 37MPa) – for comparison, the concrete typically used in sidewalks has a strength of about 3500 lbf/in² (24 MPa). One of the main component of biorock is magnesium hydroxide, another is calcium carbonate. This composition is chiefly the result of the ionic composition of seawater. Over three decades of practical experience with biorock have shown that one kilowatt hour of electricity will result in the accretion of about 0.4 to 1.5 kg (0.9 to 3.3 lb) of biorock, depending on various parameters such as depth, electrical current, salinity and water temperature. 
Biorock is cost-effective, requiring only metal bars or equivalent and a small amount of electricity. While electricity provided from fossil fuels generates CO2, biorock projects have often used solar power, wind power, tidal power, and wave power, which don't produce CO2. The resulting material is cheaper than concrete blocks in many places, depending on local electricity and cement transport costs.
As of 2011, biorock coral reef projects exist in over 20 countries in the Caribbean, Indian Ocean, Pacific, and Southeast Asia. One project is located on one of the most remote and unexplored reef areas of the world, the Saya de Malha Bank in the Indian Ocean. Other biorock projects are located in Indonesia, Maldives, Mexico, Panama, Papua New Guinea, Seychelles, the Philippines and Thailand. The most biorock projects are currently located in Indonesia, with sites in over half a dozen islands, including the two largest reef restoration projects in the world: Pemuteran with the Karang Lestari and the Gili islands with the Gili Eco Trust. Non-coral biorock projects have been conducted in other places such as Barataria Bay, Galveston, seagrasses in the Mediterranean, oyster reefs and salt marshes in New York City, in Port Aransas, and in St. Croix.
- US patent 4246075, issued 1981-01-20
- Skoloff, Brian (2007) Tire reef off Florida proves a disaster USA Today 2/17/2007
- Hilbertz, W. H. et al., "Electrodeposition of Minerals in Sea Water: Experiments and Applications", IEEE, Journal of Oceanic Engineering, Vol. 4, No. 3, pp. 94-113, July 1979
- Goreau, T. J, A Solution for Corals in Peril, A GCRA Overview, GCRA website, April 2002
- PDF of the Saya de Malha expedition 2002, rev. 1
- Goreau T.J., 2012, Marine Electrolysis for Building Materials and Environmental Restoration, http://www.intechopen.com/books/electrolysis/marine-electrolysis-for-building-materials-and-environmental-restoration
- T. J. Goreau & R. K. Trench (Editors), 2012, Innovative Methods of Marine Ecosystem Restoration; http://click.bsftransmit1.com/ViewInBrowser.aspx?pubids=9009%7C8804%7C617373%7C65313&digest=Trwjk8HjfBU2iCoETuPkbA&sysid=1
- Ortega, Alvaro, "Basic Technology: Mineral Accretion for Shelter. Seawater as a Source for Building", MIMAR 32: Architecture in Development, No. 32, pp. 60-63, Concept Media Ltd. 1989
- Balbosa, Enrique Amat, Revista Arquitectura y Urbanismo, Vol. 15, no. 243, 1994
- Goreau, T. J. + Hilbertz, W. H., "Marine Ecosystem Restoration: Costs and benefits for coral reefs", World Resource Review, Vol. 17, No. 3, pp. 375-409, 2005
- Gutzeit, Frank + Hilbertz, W. H. + Goreau, T. J., Saya de Malha Expedition, March 2002, Sun&Sea e.V. Hamburg, August 2002
- Goreau, T. J, comments quoted in Independent Study Project on Biorock, GCRA website, February 2011
- Hilbertz, W. H., Marine architecture: an alternative, in: Arch. Sci. Rev., 1976
- Hilbertz, W. H., Mineral accretion technology: applications for architecture and aquaculture with D. Fletcher und C. Krausse, Industrial Forum, 1977
- Hilbertz, W. H., Building Environments That Grow, in: The Futurist (June 1977): 148-49
- Hilbertz, W. H. et al., Electrodeposition of Minerals in Sea Water: Experiments and Applications, in: IEEE Journal on Oceanic Engineering, Vol. OE-4, No. 3, pp. 94–113, 1979
- Ortega, Alvaro, Basic Technology: Mineral Accretion for Shelter. Seawater as a Source for Building, MIMAR 32: Architecture in Development, No. 32, pp. 60–63, 1989
- Hilbertz, W. H., Solar-generated construction material from sea water to mitigate global warming, in: Building Research & Information, Volume 19, Issue 4 July 1991, pages 242 - 255
- Hilbertz, W. H., Solar-generated building material from seawater as a sink for carbon, Ambio 1992
- Balbosa, Enrique Amat, Revista Arquitectura y Urbanismo, Vol. 15, no. 243, 1994
- Goreau, T. J. + Hilbertz, W. H. + Evans, S. + Goreau, P. + Gutzeit, F. + Despaigne, C. + Henderson, C. + Mekie, C. + Obrist, R. + Kubitza, H., Saya de Malha Expedition, March 2002, 101 p., Sun&Sea e.V. Hamburg, Germany, August 2002
- Cervino, J.M. + Hayes, R.L. + Honovich, M. + Goreau, T.J. + Jones, S. + Rubec, P.J., Changes in zooxanthellae density, morphology, and mitotic index in hermatypic corals and anemones exposed to cyanide, In: Marine Pollution Bulletin 46, 573–586, May 2003
- Goreau, T. J. + Hilbertz, W. H., Marine Ecosystem Restoration: Costs and benefits for coral reefs, in: World Resource Review Vol. 17, No. 3, pp. 375–409, 2005
- R. Vaccarella + T. J. Goreau, Applicazione della elettrodeposizione nel recupero die mattes di Posidonia oceanica, in: Posidonia Oceanica, pp. 93–105, Protezione ripopolazione di praterie ed utilazzione dei residui in agricoltora, Editoriale a Cura della Provincia di Bari, Servizio Politiche Comunitarie, Assessorato Risorse del Mare, Bari, Italy, 2008
- Goreau, T. J. + Hilbertz, W. H., Bottom-Up Community-Based Coral Reef and Fisheries Restoration in Indonesia, Panama, and Palau, August 2008
- Goreau, T. J. + Hilbertz, W. H., Reef Restoration as a Fisheries Management Tool, In: Thomas J. Goreau, Raymond L. Hayes, (2008), Fisheries and Aquaculture, [Ed. Patrick Safran], in Encyclopedia of Life Support Systems (EOLSS), Developed under the Auspices of the UNESCO, Eolss Publishers, Oxford, United Kingdom, 2008
- Strömberg, Susanna M. + Lundälv, Tomas + Goreau, T. J., Suitability of Mineral Accretion as a Rehabilitation Method for Cold-Water Coral Reefs, Journal of Experimental Marine Biology and Ecology, no. 395, pp. 153–161, 2010
- Wells, Lucy + Perez, Fernando + Hibbert, Marlon + Clerveaux, Luc + Johnson, Jodi + Goreau, T. J., Effect of severe hurricanes on Biorock Coral Reef Restoration Projects in Grand Turk, Turks and Caicos Islands, Department of Environment and Coastal Resources (DECR), Grand Turk, Turks and Caicos Islands, 12-VII-2010
- Goreau, T. J., Coral Reef and Fisheries Habitat Restoration in the Coral Triangle : The Key to Sustainable Reef Management, Proceeding of Coral Reef Management Symposium on Coral Triangle Area, pp. 244–253, Coral Reef Rehabilitation and Management Program Phase II, Jakarta Selatan, Indonesia, 2010
- GlobalCoral.org: website of Dr. Thomas Goreau and the Global Coral Reef Alliance
- GCRA biorock overviews
- GCRA White Papers
- WolfHilbertz.com: website of Prof. Wolf Hilbertz with various articles
- WolfHilbertz.com: Wolf Hilbertz' seminal 1979 IEEE paper as PDF download
- Youtube video of "Coral reef restoration methods that don't work - 3"
- Youtube video of biorock coral reef restoration
- Biorock.net: website about Biorock and accretion as developed by Wolf Hilbertz and Thomas Goreau
- Biorock-Workshop.org: information on Biorock workshops
- Biorock-Thailand.com: coral reef restoration in South East Asia
- "Changes in zooxanthellae density, morphology, and mitotic index in hermatypic corals and anemones exposed to cyanide", 2003, as PDF download
- Goreau + Hilbertz: "Marine Ecosystem Restoration: Costs and benefits for coral reefs", World Resource Review, 2005, as PDF download
- Vaccarella, R. + Goreau: "Applicazione della elettrodeposizione nel recupero die mattes di Posidonia oceanica", 2008, as PDF download
- Goreau + Hilbertz, "Bottom-Up Community-Based Coral Reef and Fisheries Restoration in Indonesia, Panama, and Palau", 2008, as PDF download
- Goreau + Hilbertz, "Reef Restoration as a Fisheries Management Tool", UK 2008, on GCRA website
- Strömberg + Lundälv + Goreau: "Suitability of Mineral Accretion as a Rehabilitation Method for Cold-Water Coral Reefs", 2010, as PDF download
- "Effect of severe hurricanes on Biorock Coral Reef Restoration Projects in Grand Turk, Turks and Caicos Islands", 2010, as PDF download
- Goreau, T. J.: "Coral Reef and Fisheries Habitat Restoration in the Coral Triangle", Indonesia 2010, as PDF download