Reef Restoration And Shore Protection Projects
 At Ihuru Tourist Resort, Republic Of Maldives, Using Mineral Accretion
Preliminary Results


Thomas J. Goreau, Wolf Hilbertz, A. Azeez A. Hakeem, & Shahul Hameed


January 18 2000




Global warming and sea level rise are exceptional threats to the future of the Maldives.

Most attention has focused on the long term impacts of gradual sea level rise, but global warming is a more severe threat because it imminently threatens the integrity of the coral reefs which protect the coastlines from erosion and provides new sand supplies that create beaches and islands. If global warming damages the reefs, the impacts of sea level rise will be greatly accentuated.

During 1998 almost all branching corals in the Maldives died from high temperature, and the dead coral framework is starting to collapse from the destructive activities of internal boring organisms and the heavy grazing of parrotfish, whose populations have exploded as algae have overgrown the dead corals.

The branching corals were the fastest growing and fastest reproducing species, the fastest to colonize damaged habitat, and provided the major shelter for reef fish populations while absorbing the major fraction of wave energy before it reached the shoreline. Prospects for coral reef recovery are severely limited by the massive mortality experienced in all potential Indian Ocean source areas of new coral larvae, and the fact that temperature rise will make bleaching an annual phenomenon in the near future.

There is therefore a critical need to develop methods to protect coastlines from erosion, restore damaged reef structures, and maintain biodiversity, if the Maldivian islands and people are to survive global climate change that is out of control.

New technologies first developed on a large scale at Ihuru Tourist Resort, North Male Atoll, in the Maldives allow this to be done in a way that provides far superior results than applications of traditional technologies, at considerably lower cost, and provides additional benefits by utilizing sustainable and environmentally sound sources of renewable energy to produce building materials and mineral substrates for marine life support and enhancement.

This preliminary report outlines the results of three years work at Ihuru Tourist Resort applying Mineral Accretion Technology to restore reefs, grow shore protection structures, and maintain biodiversity. Mineral Accretion uses low voltage direct currents that can be generated by solar and tidal energy sources, to grow solid limestone on conductive materials like iron in the sea. These can be used to grow artificial reefs, breakwaters, or construction materials, to greatly accelerate coral growth and reproduction, and to create habitat for other reef organisms (Hilbertz & Goreau, 1996, US Patent).



Mineral Accretion structures can be built in any size or shape. The key factors affecting their size are the physical structure of the sea bottom, wave energies, materials available, and the source of power used.

Five structures have been built at Ihuru out of welded construction reinforcing bar. These include:

1)       A volcano-shaped artificial reef structure about 12 feet tall and 20 feet across, located in around 20 feet depth ("the Ihuru Barnacle")

2)       2) A submerged breakwater about 125 feet long, 13-20 feet wide, and 3-4 feet high, in 5 feet depth ("the Necklace")

3)       3) Three identical truncated square pyramids in around 30 feet depth ("the Trinity")

These structures were built at intervals from November 1996 through April 1998 and are powered either by solar panels or by battery chargers. In addition the steel pilings of the Ihuru pier have been wired to become another mineral accretion structure. Smaller experimental structures are attached to these larger structures.

All construction was carried out at Ihuru largely using locally available materials and skills. Solar panels were donated by the Global Coral Reef Alliance and loaned by Wolf Hilbertz, and Prof. Hilbertz and Dr. Goreau donated the special anode material.

Itemization of all the material and labor costs involved in constructing the Necklace showed a cost around 20 times less than a conventional concrete breakwater of similar dimensions.

Corals were transplanted onto these structures and attached with wires or wedged between steel bars. These corals were quickly cemented into place by the growing mineral accretion limestone forming all over the structure's surfaces. All corals and structures are periodically filmed with digital video to provide images to determine the rate of growth of both the mineral accretion frameworks and the growth rate of corals on them.



  1. MINERAL ACCRETION GROWTH. Mineral Accretion growth on the structures to date has varied from around 1 to more than 20 centimeters of thickness, depending on the local electrical field (a function of the power applied and geometry of the electrodes). This material is almost entirely rock hard limestone, similar in strength to concrete or beach rock. However selected portions that receive much higher charge, or early during the process, may form softer magnesium minerals, which grow much faster but are structurally weak. With age these convert to harder limestone.

  2. CORAL GROWTH RATES. Coral growth rates were greatly accelerated in comparison with corals of the same species on nearby reefs. The increase of growth rate caused by mineral accretion is a function of the electrical conditions at the site of attachment and of the species, but is typically around 3 to 5 times faster than normal, and can be as high as 10 times faster. Growth rates of branching Acropora corals on the structure were exceptionally high, with corals quickly filling in all available space.
    For example one colony of the branching coral Pocillopora verrucosa, which normally grows no more than 2.5 cm per year under the best conditions, grew 13 cm across in a year. Massive corals, which are slow growing, also show greatly elevated rates. Since bleaching killed portions of these colonies in 1998, we have been able to measure growth rates since bleaching in surviving portions.
    On the mineral accretion structures there has typically been 1 to 2 cm of growth since recovery from bleaching, while massive surviving corals on nearby reefs show only around 0.1 to 1 cm of growth. We are monitoring corals on and off the structures to determine long-term growth rates as a function of coral species. We will publish detailed scientific papers once the thousands of images taken over the last few years have been quantitatively analyzed using special new software to reconstruct each coral's three dimensional shape changes from stereo image pairs.

  3. CORAL SURVIVAL FROM BLEACHING. Almost all the branching corals died during the severe heat that killed most of the corals in the Indian Ocean during 1998. In sharp contrast, the survival of massive corals after bleaching was many times higher on the mineral accretion structures than on surrounding reefs. Most of the massive corals survived on the mineral accretion structures, while most of them died in the reef. Surviving corals were largely killed on the uppermost surfaces, especially those on top of the Necklace that were subjected to aerial exposure at low tide.
    Higher survival is due to the better energy status of corals benefiting from mineral accretion, which allowed them to survive the starvation and physiological stress that killed most bleached corals. A few branching coral species that did survive have since shown exceptionally rapid growth rate on mineral accretion. Quantitative counts of surviving and dead corals are being prepared from videos of the mineral accretion structures and the surrounding reef taken before and after bleaching.
    Dead branching corals on the Barnacle were replaced with head corals, but they were left in place on the other structures. The Barnacle is now almost completely covered with live corals, and may have the highest concentration of live corals now to be seen in the Maldives.
    Because the artificial reefs have much higher density of live corals than surrounding reef, they unfortunately also serve as an oasis in the desert for starving coral-eating snails and starfish (Drupella and Acanthaster), which can do a lot of damage to corals in a short while if not controlled. The best results will be gained from regularly maintained structures, like weeding a garden to get the greatest crop growth.

  4. BIODIVERSITY CONSERVATION. Biodiversity maintenance functions of the mineral accretion structures became starkly clear in the aftermath of bleaching. Due to the higher coral survival and higher growth rates the mineral accretion structures now have much higher live coral cover than surrounding reefs, and as the result many fish and other marine organisms dependent on live coral for either food or habitat have concentrated their populations in them.
    A sharp contrast can be seen in fish diversity and abundance between the structures and the surrounding reef. Since most dead corals on the reef have been overgrown by algae, there has been a population explosion of the algae-eating fish, primarily parrotfish, surgeonfish, damselfish, and rabbit fish, and large schools of these now roam the reef, giving the impression of a vibrant and healthy fish population.
    However most of the other reef fish have severely declined. One of the most attractive of all reef fish families, the butterfly fish, which suck mucus from the surface of living corals, is greatly reduced on the reef, but small permanent populations are always found on the mineral accretion structures. Large schools of brightly colored Pseudanthias and other fish that feed on plankton in the water, and hide between the branches of live coral, were a special feature of Maldivian reefs, but they have been greatly reduced since they will not shelter in dead coral.
    Nevertheless on the mineral accretion structures one can find permanent populations of these fishes. Several very attractive families of "normal" reef fish, including oriental sweetlips, giant moray eel, and triggerfish now migrate between the mineral accretion structures, and are rarely found outside of them. Further changes in design, by changing the sizes and shapes of mineral accretion structures could be used to promote colonization of certain groups of fish, lobster, and octopus, by providing holes of the size they prefer.
    All of the mineral accretion structures have become major cleaning stations, sites where cleaner wrasses and cleaner shrimps remove parasites from reef fish. These are exceptional places to observe reef fish because they peacefully line up to be cleaned, and high diversity and relaxed behavior is best seen at such locations.
    Despite their small size in comparison to the natural reef, the mineral accretion structures have become major refuges of reef organisms that are now rarely seen on the reef, and are serving as an oasis of high biodiversity, maintaining habitat for many reef species until the surrounding reef can recover.
    Corals on the mineral accretion structure, because of their higher growth rate and healthier metabolism, will reproduce sooner and more, and so play a key role in restocking the surrounding reefs. Several coral nurseries have been established to rapidly propagate the few species of high temperature tolerant branching coral species that survived bleaching.
    Several small mineral accretion structures have been built that receive low current, in order to provide clean limestone substrate that is far more suitable for baby corals to settle and grow than the surrounding algae-covered dead corals. Although numerous new corals have been observed on them, it is still too soon to statistically compare their numbers with that on surrounding reef (because they are still few and small). However we are confident that within a year or two the much higher rate of baby coral settlement on them will be clear.

  5. 5. SHORE PROTECTION. Shore protection breakwaters built from mineral accretion are steadily growing in size and strength as the solid rock layer gets thicker and absorbs more wave energy.
    The structures are permanently anchoring themselves by cementing bedrock and sand around their bases and steel rods driven into the sea floor. Damage to the accreting layers of limestone (by anchors, boats, or drifting tree trunks) is readily repaired by renewed mineral accretion, which preferentially fills any cracks. This feature of self-repair is unique to Mineral Accretion structures.
    Mineral Accretion structures, if sufficiently large, are capable of reducing wave energy at the shoreline and hence reducing coastal erosion rates. Waves passing through the Necklace are being noticeably slowed down as they lose energy by friction with the structure, and sand is beginning to accumulate beneath them. Its efficiency as a wave energy absorber will greatly increase by piling more dead coral rubble inside to make it a more solid wave barrier, now that the framework is strong enough. The steel dock pilings are growing a layer of limestone on top of them,
    The rusting of the submerged pilings has been completely halted, and in fact previous rust has been converted back to metallic iron by the protective cathodic action of the electrical currents. As a result, these pilings are completely protected from corrosion, and are now permanent. They will never need to be replaced again. Only the portions above the high tide mark that are not protected are rusting, and will eventually need to be replaced.
    Steel bulkheads used at Male and Hulhule could be similarly protected. The large areas of coral rubble seawalls in the Maldives, which generally need to be rebuilt after a few years due to storm damage, could similarly be made into permanent structures by cementing them together with accretion materials. These structures would get stronger with age, rather than weaker, and would need little rebuilding as long as low levels of electrical current are applied.

  6.  CONSTRUCTION MATERIALS. Experimental work at Ihuru has shown that limestone structures can be grown in any size or shape, allowing the production of prefabricated construction panels that could be used as building materials. In addition we have had excellent success with making bricks and building blocks in molds, using a mixture of reef sand and ground up mineral accretion, which cements the sand together into solid blocks.

  7.  RENEWABLE ENERGY PRODUCTION. Energy for mineral accretion at Ihuru is provided using solar panels and fossil fuel generated electricity. However at many sites in the Maldives, wherever currents significantly exceed 1-2 knots, Gorlov turbines could be used to generate electricity.
    Every atoll in the Maldives has tidal passes which could supply much of the energy needed for both large scale shore protection, reef restoration, construction materials, and energy supplies, using completely untapped, sustainable, non-polluting, and indigenous tidal energy resources. Mineral accretion and Gorlov turbines can be used to produce hydrogen, a non-polluting fuel, which could be exported.



The work done at Ihuru has proven that Mineral Accretion can resolve major environmental problems in a cost-effective way that no other technology can. Visitors have come from around the world to observe the Ihuru structures, and they have been featured on television programs by the BBC, German, Japanese, and Italian networks, diving magazines, and newspaper articles worldwide as a unique new approach to sustainable ecological engineering.

These projects received international recognition by restoration ecologists when the top award of the Society for Ecological Restoration, the Theodore M. Sperry Award for "pioneers and innovators in restoration", was awarded to Wolf Hilbertz and Tom Goreau at the 1998 annual conference in Austin, Texas. These new technologies could be readily applied on a much larger scale to help resolve the critical environmental problems the Maldives will face in coming years from global warming and sea level rise. They are simple to learn and apply.

Although new concepts must be learned, the skills possessed by any village electrician and welder can be readily applied. Maldivians have already demonstrated their mastery of these methods at Ihuru. The inventors and patent holders of Mineral Accretion, Wolf Hilbertz and Tom Goreau, are prepared to transfer their knowledge to Maldivians at cost, without seeking royalties or profits on the technology, because of the great significance and urgency that they have for the Maldives and for all low-lying tropical island nations.

The new technologies can be applied on any scale, and are applicable to even the smallest and most remote communities as well as the largest. The skills for maintaining and repairing mineral accretion structures are quickly acquired locally, following which no expensive foreign experts are needed to maintain them.

Decisions to try innovative new approaches must be made by Maldivians based on choosing the best available technology for their needs, and recognizing that foreign funding agencies and expensive "experts" are simply blindly copying the failures of the past and inhibiting development of new endogenous skills.

While growing large scale mineral accretion seawalls may seem grandiose, the real question is not whether more seawalls will be needed in the Maldives in coming years but whether mineral accretion is a more cost-effective and sustainable alternative to concrete and rock walls.


  1. Maldivian environmental policy makers should compare the mineral accretion structures and surrounding reefs for themselves. The results are hard to believe without seeing it for oneself.


  1. A workshop should be held to train all interested Maldivians in the methods, design, construction, maintenance, and repair of Mineral Accretion structures. This workshop should be held in Dhivehi, and taught by the staff at Ihuru Tourist Resort who has worked on these projects. Funding should be sought to provide the necessary materials so that each participant can conduct a pilot project on their own island.


  1. Large-scale Mineral Accretion coral nurseries should be constructed to greatly accelerate the growth, reproduction, and settlement of new corals in bleaching damaged reefs, and to maintain diverse reef fish populations. Rare surviving coral species should be sought and propagated. The next few years will be the most critical for accelerating ecosystem recovery.


  1. Pilot projects in the production of construction materials should be started. Many of these projects could be designed to allow the hydrogen produced by Mineral Accretion to be trapped and used as a non-polluting fuel.


  1. Large scale submerged breakwaters should be grown to protect the coastlines of inhabited and tourist islands from erosion. These will be especially needed in the next few years as the dead coral breaks up and as sea level rise continues. These should use a new modular construction system that is far more rapid to construct than the welded structures used previously. A major focus should be development of new approaches to baffle waves and cause them to lose their coherence and strength in situ instead of reflecting them with a solid sea wall, as this will be far more efficient in terms of materials.


  1. Existing seawalls and dock pilings, whether of steel bulkheads, concrete, or rock rubble should be protected by using Mineral Accretion to halt corrosion, cement them together, and virtually eliminate repair and replacement costs. These should use renewable energy sources such as photovoltaics and ocean currents.


  1. Artificial islands should be protected using mineral accretion breakwaters and seawalls. The obvious place to start is to protect the greatly expanded new dredgefill at Hulhule, which is highly vulnerable to sea level rise.


  1. Pilot projects should be rapidly initiated using Gorlov turbines to create potentially almost unlimited energy supplies from the intense tidal currents in the major tidal passes of all Maldivian atolls. Such projects should begin in the pass between Male and Hulhule, where Gorlov turbines can be used to generate the energy to protect the coastline of the new artificial island at Hulhule and to provide electricity.



We thank Ahmed Mujuthaba for supporting these pilot projects and helpful advice, and Hassan Maniku for initial contacts.