Restoration of Coral Reefs at Ihuru Island
North Male Atoll, Maldives

June 11 1998


This project by Wolf Hilbertz & Thomas J. Goreau was nominated for the 1998 Society for Ecological Restoration Awards:


This project has generated healthy and diverse coral reefs in areas of the Maldives where corals were absent, using a unique new technology which uses solar panels to grow large limestone structures in the sea, speed up the growth of corals, and provide new habitat for fish and other coral reef creatures. This project demonstrates for the first time the possibility to economically restore damaged coral reefs to vitality and create new ones to protect beaches and shorelines from erosion on a large scale. It pioneers the use of sustainable energy to rejuvenate the most complex marine ecosystems and establishes a remarkable new method which will be needed on a large scale in coming years to restore coral reefs damaged by global warming, pollution, sedimentation, and natural or human physical destruction, and to protect whole islands from erosion and rising sea level.

Global Needs for Reef Restoration:

Coral reefs are the most species-rich, complex, and beautiful marine ecosystems. They are also the most economically important due to the ecosystem services they provide by supplying seafood, beach sand, tourism, limestone rock and sand for construction, and protection of the shore against waves. Coral reefs around the world are dying back due to human-caused changes in water quality which increase water temperatures, nutrients, and sediments, as well as from direct physical damage from dredging, anchoring, destructive fishing techniques, and other intensifying human stresses. Most  reefs near populated areas or tourism resorts are dying or dead. High temperatures related to global warming and the outbreak of coral diseases are taking severe tolls in all reefs, especially in remote reefs which have not been previously directly affected by humans. In the first half of 1998 there has been massive death of corals due to unprecedented hot water conditions across the southern Pacific, Atlantic, and Indian Oceans. This is causing severe declines in catches, stocks, sizes, and diversity of fishes, greatly increased erosion of beaches and coastal structures, and loss of tourism revenues. If coral reefs continue to deteriorate the economies of over 100 coral reef countries will be severely affected, and several could vanish entirely due to rising sea level. Limitations of previous approaches: Many projects have claimed to "restore" reefs. These generally consist of transplanting coral fragments, but most of these soon die either due to being inadequately secured against rolling or physical impact, or because corals at the site originally died due to inadequate water quality, which also kills any new transplants. Although discarded cars, ships, airplanes, concrete blocks, rubber tires, fly ash, and other trash have been called "artificial reefs" these structures are found to have few hard corals or a normal diversity of reef organisms: instead they are sparsely covered with a limited variety of sponges, soft corals, and other weedy organisms. Such structures may provide hiding spaces for fish, but they steadily deteriorate as they rust, corrode, and leach toxic chemicals, crack, crumble, and eventually collapse, turning into projectiles which damage real reefs in storms. Despite ambitious claims made on short term results, such projects show very high mortality of transplanted corals within a year, and none are known to have increased the abundance of living corals over significant areas or to have created habitat for a normal reef ecosystem. In addition their high cost makes them unfeasible on a large scale.


Mineral Accretion Technology:

A new technology, mineral accretion, uses safe low voltage electrical currents to precipitate dissolved limestone minerals from seawater by creating chemical conditions causing mineral deposition, which would not happen by itself. Rock-like limestone minerals crystallize out of the water, generating a solid growing structure. By creating conditions allowing mineral accretion,  mineral accretion causes corals and all organisms with limestone skeletons (such as clams, oysters, etc.) to grow much more rapidly. Because local water quality conditions have been created favoring limestone deposition, these organisms can grow their calcareous skeletons without having to spend large parts of their metabolic energy on mineralization, thus freeing energy for more rapid tissue growth. Mineral accretion technology, developed originally in the 1970s by architect Wolf Hilbertz to generate alternative construction materials, has been improved and applied to coral reef restoration by Hilbertz and coral reef scientist Dr. Thomas J. Goreau over the last ten years.


Results to Date:

Pilot work on reef restoration using mineral accretion has been carried out at sites in the Indian Ocean, Caribbean, and Pacific. Corals transplanted onto mineral accretion cement themselves solidly to it and proceed to grow at extraordinary rates. Young corals settle and grow on mineral accretion, and all other reef organisms are attracted. Results showed that corals were able to grow at record rates even in areas where coral reefs had been killed by pollution, since the limestone-producing organisms receive a boost which their soft weedy competitors do not. Heavy recruitment of young corals was stimulated in an area where no natural settlement was taking place. Since 1996 the major focus has been on projects in the Maldives, one of the countries most threatened by sea level rise, where the very existence and persistence of the islands and islanders depends on healthy coral reefs. Many Maldivian reefs have been damaged by mining of corals, the only locally available building material, with the result that serious erosion problems are requiring large-scale seawall construction. Projects in the Maldives successfully completed to date include the creation of a 15 foot high artificial reef to create a new coral community on a sloping bottom, a 130 foot long breakwater reef to protect a beach, and stimulation of coral communities in situ to speed up their growth. These are powered by a variety of power sources, including used solar panels recycled from the world's largest solar power plant (dismantled) and battery chargers. Coral transplants have nearly all survived, and are growing at very rapid rates. For example a young coral which settled spontaneously grew to a diameter of 13 centimetres in less than a year, although the normal growth rate of this species is 2.5 centimetres per year. Corals are rapidly covering the structures and have created habitats whose diversity rivals that of natural reefs.


Large numbers of fish forage, school, or sleep in new artificial reefs that have cemented themselves solidly to the bottom are slowing down waves, reducing erosive forces at the shoreline. The cost of these natural and growing breakwaters is around one fiftieth of conventional seawalls.


Advantages of Mineral Accretion for Coral Reef Restoration:

Mineral accretion avoids the drawbacks of all other methods of reef restoration and provides many unique benefits. Because it is the only method which increases the growth rate of corals, both transplanted and in-situ, it is capable of stimulating existing reef growth and of creating new reefs. As it is the only method which produces the natural materials that make up coral skeletons, the reef structure, and reef sand, young corals settle and grow preferentially on it. By creating conditions of healthy coral growth, all other types of reef organisms migrate into such structures. Because the structure is solid and attached to hard bottom, it is capable of providing the wave absorbing services provided by healthy coral reefs. Because it is growing upwards at several centimeters per year it is capable of keeping up with sea level rise. Steel wires, mesh, or frameworks in mineral accretion structures do not rust because they are electrically protected from corrosion, so they do not undergo the deterioration characteristic of all other materials. Not only do mineral accretion structures become steadily stronger with age, they are also self-repairing: any cracks or breaks caused by severe storm waves are preferentially filled in. The cost of mineral accretion coral reefs is a fraction of seawalls, and the degree of protection constantly increases, while seawalls progressively deteriorate and eventually collapse. Mineral accretion reefs can be made in any size or shape. They can be powered purely by renewable energy from solar panels, windmills, or tidal current electrical generators.


Implications for Global Reef Restoration, Shore Protection, and Renewable Energy Development:

These results show for the first time that it is possible to restore coral reef diversity, function, and ecosystem services in a cost-effective manner. It is now possible to grow coral reefs and breakwaters in places where reefs have been destroyed, and to rejuvenate degrading reefs. Whole shorelines can be protected from erosion and rising sea levels. Goreau and Hilbertz are currently  working with the Maldivian Government to expand applications of mineral accretion to protecting entire islands from erosion and to generate alternative construction materials. Pilot projects in the Union Territory of Lakshadweep (India), Seychelles, and Bali (Indonesia) are underway and will be expanded as soon as funding can be found. A project is in development with the Cuna Indians of Panama to grow artificial islands from mineral accretion to replace traditional islands built from mined corals. Projects are planned with the atoll nations of the Pacific (Tuvalu, Kiribati, Marshall Islands, Micronesia, Palau). A new development involves use of the newly invented Gorlov turbine to develop tidal current flows as a major untapped renewable energy resource. Introduction of such radically novel technology has many hurdles to overcome unless people can see for themselves that it works. Existing projects have clearly demonstrated its unique value, but lack of awareness of its potential has inhibited funding for its large scale application. Recognition by the Society for Ecological Restoration will emphasize that marine ecosystems need to be restored as much as terrestrial ones and greatly increase the chances that reef restoration can be carried out on a scale which matches the increasing global demand before it is too late.



Results of preliminary work was presented at the 8th International Coral Reef Symposium in Panama in 1996. An illustrated article will appear in the summer 1998 issue of Ocean Realm. A detailed article is in preparation for submission to Ambio. Short magazine, newspaper, and television pieces have come out in Germany, Britain, France, Japan, Denmark, the United States, the Maldives, and the Seychelles.

The projects can be seen by arranging permission from the Maldivian partners in the project, Azeez Hakeem and Ahmed Mujuthaba of Ihuru Tourist Resort, North Male Atoll, the Maldives ( tel: (960)-44-5932; fax: (960)-44-5933;   email: ihuru@dhivehinet.net.mv ).

For further information please contact Dr. Goreau or Prof. Hilbertz.