Pemuteran Coral Reef Restoration Project
Progress Report: May 29 2001

Wolf Hilbertz and Tom Goreau

New photos of the Pemuteran project:

Additional photos  of Bali's reef restoration project.  

Additional Bali Reef photos One

Additional Bali Pictures Two

Twenty eight Biorock™ coral nursery structures have recently been installed in the Pemuteran Village Marine Protected Area in Northwest Bali, Indonesia, in cooperation with the Municipality of Pemuteran, Gahawisri (the Balinese Watersports Federation), local dive shops and hotels, and other local stakeholders.  With a total length of 300 metres situated in an area of 2 hectares, this is the largest Biorock coral reef nursery and restoration project worldwide, exceeding the combined sizes of all other ongoing projects in the Pacific, Caribbean, and Indian Ocean.

The project, although still in the early stages, already has the majority of local coral species in cultivation. Their enhanced growth rate, reproduction, and resistance to environmental stress provides a critical reservoir of healthy corals to resist future hot periods caused by global warming and to restore damaged reefs and vital fishing areas once destructive human practices can be halted.

Bali’s coral reefs have been severely damaged in recent years due to use of bombs and cyanide by fishermen, excessively high water temperatures linked to global warming, and other stresses.

The Pemuteran area is unique because no other part of Bali has such large areas of shallow reef, and these are accessible to divers and snorkellers because the region lacks the extremely strong currents and waves that characterize other coastal areas of Bali. However, Pemuteran reefs have suffered greatly from damage by destructive fishing because the low currents make it far easier for fishermen to retrieve fish killed by bombs or paralyzed by cyanide. Pemuteran village residents have taken action to prevent use of these destructive methods in their reefs, whether by locals or by outsiders.

However, the amount of damage is so great that action is urgently needed to restore reef habitat for tourism and fisheries. Because of mounting local concerns about reef deterioration, Yos Amerta, President of Gahawisri (the Bali Branch of the Indonesian Watersports Federation), invited Wolf Hilbertz and Tom Goreau to start restoration projects in Bali, following a workshop in coral reef restoration sponsored by Action Asia Magazine at the Asian Dive Exposition in Bangkok in May 2000. 

Coral nurseries built using the Electrolytic Mineral Accretion Technology (Biorock™) of Hilbertz and Goreau provide unique advantages for restoring coral reefs. Corals grown on mineral accretion are exceptionally brightly coloured and rapidly growing, support dense fish populations, and are more resistant to all environmental stresses except bombs and poisons. The first projects in Indonesia were built in the Pemuteran Marine Protected Area in June 2000 by Hilbertz and Goreau, working with Yos Amerta and Gahawisri, in front of the Yos Dive Shop at Pondok Sari, and in front of Reef Seen Aquatics. Three more structures were added in October 2000 in front of the Village Sea Temple, during an international training workshop on coral nursery construction (see Workshop Report for details). The Workshop was funded by a grant from the Leslie Jones Foundation to the Global Coral Reef Alliance’s coral reef restoration program, and donations in kind from Yos Dive Shop and Pondok Sari Hotel. The success of these structures in stimulating rapid coral growth was apparent within months, leading to requests to greatly expand the project. Taman Sari Hotel donated further funds to support the construction of new projects in March 2001. The initial results of this phase are discussed in this progress report. The earlier structures are described in the previous workshop report.   

18 new coral nursery structures were built and installed in March 2001 along the length of the Pemuteran Protected Area, in front of Taman Sari Hotel. These structures are located in an area parallel to the shore, about 50-80 metres from the coastline, in waters ranging from about 3 to 7 metres deep. They are roughly lined up, forming a natural snorkelling and diving trail.  

The new coral nursery structures are made of welded construction steel bars, mainly of 1 centimeter and 1.3 centimeter diameter. They are built in a variety of shapes. One structure, called the Nautilus, is 3.5 m high 3 m wide, and 11 m long, in the form of an ellipsoidal pyramid. Six structures, called the Flowers, consist of funnels of about 2.5 m high and 3-5 m diameter. These structures have numerous arc-like pockets along their sides. Another set of 7 structures, called the Caterpillars, are 12 m long, about 2 m wide and 2 m high, and consist of open downward and upward pointing arcs. Two structures are bamboo-steel composites, composed of 12 m horizontal bamboo logs, with steel bars driven through their length, supported by steel arc legs. One structure has a single length of bamboo, while the other consists of two such units end to end. Another structure, the Big Bamboo, is built only of bamboo, wrapped with 2 mm copper wire. Following application of electrical current, the steel structures proceed to grow a white limestone layer, providing a substrate for coral growth. While the bamboo elements are not electrically conductive, the steel bars inside them or the copper wire around them grow limestone on their surfaces, which is expected to mineralize the adjacent bamboo wood over time. Another project consists of mesh, 1.2 m wide and 25 m long, laid over the bottom. An additional project on the other side of the bay in front of Reef Seen Aquatics uses wires directly attached to corals.

All structures are charged by power supplies located on the adjacent land. They are located in two enclosures at Taman Sari Hotel, in Archipelago Dive shop at Taman Sari, in the Pemuteran Village Barong Art Shop, in Yos Dive Shop at Pondok Sari Hotel, and at Reef Seen Aquatics. Electricity is donated by the operators of these facilities. The cathodic structures and anodes are connected to the power supplies by cables which are buried in the beach and laid on the sea floor. All the structures combined receive up to about 4.5 kilowatts of power. Many structures receive power through several cables, and all are wired to each other so that power is shared throughout, allowing them to continue operating even if their direct power cables are severed. The power supplies are wired in parallel through common buses, so that if one fails the others will take up the load. As a result of this redundant design, the system is highly robust to failure of any particular cable or power supply.

Because Bali lies close to the centre of the world’s coral reef species diversity, most of the world’s coral species are found in the Pemuteran area. Corals were collected for tranplantation onto the structures from sites in the Pemuteran area, including sites within the protected area and nearby fringing and offshore reefs. Corals were transported in large plastic buckets filled with seawater and attached to the structures as soon as possible. Most corals were simply wedged into specially designed spaces between the structural elements of the structures, and needed no further attachment. Other corals were attached by wires, or placed on or next to the structures.

 Coral selected for transplantation consisted almost entirely of naturally broken fragments that were found lying on reef slopes or buried in mud below them. Large numbers of corals were found loose, often having had their bases undermined by boring worms, clams, and sponges. Many of these corals were previously severely damaged by abrasion or burial, often with significant fractions dead. The purpose of choosing these damaged fragments was to rescue corals that would have almost surely soon died as the result of physical injury, and to avoid damaging healthy corals whenever possible. Often only a very small fraction of the coral was left alive as a result of previous injuries, but in almost all cases these living portions proceeded to grow well after attachment. A few totally dead corals were attached because some divers involved in collection were insufficiently experienced at identifying live corals. Although the focus was on stony reef-building corals, some soft corals, sponges, tunicates, and anemones were also transplanted.

 Because the naturally generated coral fragments most likely to be found by divers tended to be the most abundant branching corals (primarily Acroporas, Pocilloporas, Porites, and Seriatoporas) these species tended to be over-represented in the collected transplants. A special search was made for rarer coral species unlikely to be found as natural fragments, such as massive or encrusting corals. Where these could not be found loose, small fragments were broken off and transplanted to ensure that the maximum species diversity of the area was represented. These were often taken from colonies growing near to the structures. Some massive and cryptic encrusting corals found in the area were never found in sizes or shapes that could easily be broken off and transplanted, and are under-represented on the structures.  

Indonesia has 581 of the world’s 793 known reef building coral species, i.e. 73.3% (Veron, 2000). At least 66 of the 82  reef building coral  genera in Indonesia (80.5%) and of the 111 genera worldwide (59.5%) are already being cultivated on the Pemuteran Coral Arks (see appended list of genera). It is likely that several more genera are also found on the nurseries but were not identified, especially cryptic encrusting species on the undersides of other coral colonies. 

Coral nurseries receiving adequate power quickly turned white as mineral accretion grew on them, and began to cement themselves to the reef bedrock. Almost all live coral fragments were quickly cemented in place by mineral accretion, and proceeded to grow rapidly over it. New coral skeleton growth was clearly visible in as little as a few days. Because these corals have only recently been transplanted and the power applied, it is too soon to compare detailed differences in growth rates between species, but even in the first few weeks some trends became apparent. The Acroporas and Montiporas seem to be most responsive, quickly overgrowing the mineral accretion, often completely growing around it, and rapidly forming dense arrays of new branches. Some Acropora colonies formed hundreds of new branches that grew about a centimeter in less than a month, and many corals show clear changes in growth orientation and unusually dense and compact branching after transplantation. These corals are also distinguished by very bright colors, but on some structures on which connections failed due to faulty cables, these color and growth form changes were not apparent until after the cables were replaced and power restored.  

Only very low levels of coral mortality were observed. Some was due to corals that were dislodged from the structures by waves, divers, or fish before they were fully attached. Some corals were so severely damaged before transplantation that they died of their injuries. Other corals were infested with the coral-eating snail Drupella, which can quickly kill colonies if they are not removed. These were found in swarms of plague proportions on the reef, and are currently the major cause of coral mortality. Some coral species appeared to have minimum sizes for successful transplantation. While most pieces as small as a few millimeters across were successfully transplanted, some of the larger polyped corals appear to need larger areas of tissue to be successfully transplanted. Certain species of thin leafy corals or delicate branching corals proved to be hard to transplant because they tended to break while being attached. Some corals that were collected in deeper areas or on walls bleached when transplanted into shallow water, but most recovered in a few weeks. Only a tiny handful of corals were observed to die for no obvious reason, and it is possible that these were diseased. There was no species of which at least some fragments did not succesfully attach and  grow.   

Following the establishment of new coral growth on the structures, fish and marine invertebrates began to be rapidly attracted wherever the corals were sufficiently dense. Large populations of many small reef fish that live only around living corals quickly found the coral transplants and established themselves. The presence of many juveniles and rapidly increasing populations of these species indicate that they have become self-sustaining populations. Dense schools of young fishes of many species were observed to be attracted to the mineral accretion corals, apparently choosing them as sites to metamorphose from larval stages into juveniles. Snappers quickly found the structures an attractive place to hide in the day time, forming schools so dense that it was often impossible to see the other sides of the structures. Batfish became regular inhabitants. Damsel fish and cleaning fishes quickly established territories on the structures. Other species of reef fish come to graze on the thin coating of algae growing on the less charged structures, and many other species simply pass through them in their search for food. Most fish species appear to be attracted, and none to be repelled, by the electrical currents. In addition many invertebrates, including attached tunicates and mobile squid, cuttlefish, sea urchins, and starfish, have established themselves.        

These projects are largely at the very earliest stages. Due to the need to replace faulty cables, coral transplantation was greatly slowed down, and most structures have far too little coral on them. Because of faulty cables, many of the structures were receiving insufficient power until this problem was corrected. The corals on these structures were notably less vigorously growing and brightly coloured than those structures receiving full power, and the mineral accretion on these structures tended to build up a dark surface layer of algal growth that was not apparent on those fully charged, which were white in appearance. Some of the structures only began to show good rates of mineral accretion and coral growth immediately after the cable problems were corrected, but beneficial results should be dramatically apparent in the coming weeks and months.  

The more dense the coral transplantation on the Coral Arks, the more rapidly they will build up permanent reef fish populations and look like natural reefs. Intensive continuing transplantation is needed on those structures with few corals so far. While the percentage of each structure covered with lving coral varies between structures, being highest on some of the flowers, the overall average is less than 5%. There needs to be a concerted effort to increase the amount of coral fragments transplanted, especially onto the Caterpillar structures. The lower portions of the Nautilus need much more coral, as do many of the flower structures and the steel portions of the bamboo structures and the mesh. The corals and their growth need to be periodically monitored by video, at least twice a year, and if possible four times a year, to get a handle on seasonal changes.  

The stimulation of coral growth is likely to vary strongly between different coral species and between structures receiving different amounts of current. Therefore it will be especially important to monitor the growth of all the corals on all the structures in order to determine which species do best under different rates of charging. Growth rates should be monitored from time to time using video images. Many of the coral fragments transplanted came from known nearby colonies, and both the transplants and the mother colonies need to have their growth monitored to allow determination of the amount of growth enhancement from mineral accretion. In addition it will be important to try to transplant and cultivate the fullest range of local species, including those that are still under-represented or absent from the structures. 

The best results will come with periodic maintenance. Power supplies need to be checked and faulty capacitors and fuses replaced as needed. Cables need to be kept buried in the ground where they cannot be damaged by people, horses, or boats, and cables in the wave breaking zone should be sheathed in PVC pipe to prevent the cables rubbing on rocks and breaking during storms. Anodes need to be checked from time to time to determine if they are still functioning, and new connections made if needed. Corals that are broken or dislodged by waves, divers, or fish should be promptly repositioned or they will die from burial or abrasion. Coral eating pests, such as crown of thorns starfish or Drupella snails need to removed and buried on land. Algae should be removed where it may overgrow coral. Structures should be periodically inspected to ensure that they are growing well. A decrease in the formation of bubbles on them, slow growth, pale corals, or dark excess algae on the mineral accretion substrate instead of a white colour, indicate that power is insufficient, and probably that a cable needs to be repaired. 

Even in the earliest stages, these projects show dramatic results in increasing coral growth and fish populations. The projects are a major attraction for divers and snorkellers. They show great promise for restoring damaged coral reefs, and need to be applied on a large scale wherever coral reef deterioration has been seen, especially across Indonesia, the centre of tropical marine biodiversity, to maintain coral reef ecosystems in the face of accelerating threats from global warming.  


A project of this magnitude was only possible because of the large number of people who helped at every level. We thank the entire staff of Taman Sari, who provided a congenial and helpful atmosphere for the hard and sustained work needed during the installation of this project. We would also especially like to thank the following:

Welders: Pemuteran Welding Shop

Electricians: Ma Danis, Gusti Ngurah, Moyo

Divers, nursery installers, cable layers:  Seno Suwarno, Ketut Santika, Komang Astika, Wayan Kantra, Kadek Alo, Wayan Sutama, Kadek Surata, Suryono, Ketut Dastra, Herman, Gede Riasta, Wayan Suantara, Ayok Asongko, Wayan Sutama, Gede Kartika, Putu Budiyasa, Wayan Galang, Lars Withen, Andy Taylor

Coral collection and transplantation: Seno Suwarno, Ketut Santika, Rani, Narayana, Prem, Gandhi, Lars Withen, Antoine Guivarch

Community support: Yos Amerta (Gahawisri), Wayan Werta (Pemuteran Kepala Desa), Ketut Sudarma (Pemuteran Fishermen’s Cooperative),             Agung Prana

Filming: Michael Balson, Maria Masta, Rani

Funding:   Taman Sari Hotel, Leslie Jones Foundation


PHOTOGRAPH PLATES (all by Rani E. Morrow-Wuigk) 


Plates 1 through 4 show all of the coral nursery structures.

Plates 5 through 6 show close up views of corals and fish on the nurseries.



(following the order of J. E. N. Veron, 2000, Corals of the World)

Many species (especially Acropora, Montipora, Fungia, Goniopora) cannot easily be identified without detailed microscopic examination of the skeleton. We have limit listing to genera. The Arks are growing many corals that cannot be clearly identified from Veron’s book because they differ greatly in colour patterns and forms from those described. These could either be locally variant populations of known species or species that have not yet been described.


Montipora (dozens of encrusting, foliose, and branching species)


Acropora (perhaps a hundred distinct types)

Astreopora (several species)




Pocillopora (several species and morphotypes)

Seriatopora (half a dozen species)

Stylophora (several)

Euphyllia (several)



Galaxea (several)




Pavona (several)

Leptoseris (several)



Pachyseris (several)

Cycloseris (several)




Fungia (many)








Echinophyllia (several)

Oxypora (several)


Pectinia (several)

Hydnophora (several)


Merulina (several)


Turbinaria (several)


Acanthastrea (several)

Lobophyllia (several)

Symphyllia (several)


Favia (several)


Favites (several)

Goniastrea (several)




Montastrea (several)



Cyphastrea (several)

Echinopora (several)


Porites (dozens of branching and massive species)

Goniopora (several)