ABSTRACT

Introduction ��������������������������������������������������������������������������������������������������������������������������������������48 Methods �������������������������������������������������������������������������������������������������������������������������������������������48

Study Sites �����������������������������������������������������������������������������������������������������������������������������������48 Barrang Lompo Island ����������������������������������������������������������������������������������������������������������� 49 Samalona Island ��������������������������������������������������������������������������������������������������������������������� 49 Pemuteran Village ������������������������������������������������������������������������������������������������������������������ 49 Gili Trawangan ����������������������������������������������������������������������������������������������������������������������� 49

Materials ������������������������������������������������������������������������������������������������������������������������������������������ 49 Results ���������������������������������������������������������������������������������������������������������������������������������������������� 52

Barrang Lompo Experiment ������������������������������������������������������������������������������������������������������� 52 Survival Rates ������������������������������������������������������������������������������������������������������������������������ 52 Coral Growth Rates ���������������������������������������������������������������������������������������������������������������� 52

Samalona Experiments ��������������������������������������������������������������������������������������������������������������� 53 Water Quality �������������������������������������������������������������������������������������������������������������������������54

Pemuteran Experiment ����������������������������������������������������������������������������������������������������������������54 Gili Trawangan Experiments ������������������������������������������������������������������������������������������������������ 55

Coral Growth �������������������������������������������������������������������������������������������������������������������������� 55 Fish Populations ��������������������������������������������������������������������������������������������������������������������� 55

Discussion ���������������������������������������������������������������������������������������������������������������������������������������� 57 Conclusion and Recommendation ��������������������������������������������������������������������������������������������������� 57 Acknowledgments ���������������������������������������������������������������������������������������������������������������������������� 58 References ���������������������������������������������������������������������������������������������������������������������������������������� 58

INTRODUCTION

Coral reefs are an invaluable coastal ecosystem in tropical areas, because they provide not only significant amount of food for humans but also offer important physical protection for coastal areas� The hard structure of coral reefs is mainly formed or constructed by scleractinian corals (Class Anthozoa), by precipitating calcium carbonate into their skeleton (Veron 1993)�

Indonesia has the largest area and highest biodiversity of coral reefs of any country in the world� In spite of their high economic value, Indonesian coral reefs face serious problems from heavy reef degradation mainly due to anthropogenic factors, such as destructive coral reef fishing (dynamite, cyanide, and overfishing), coral mining, pollution, and sedimentation� In addition, phenomena such as bleaching, Acanthaster outbreaks, and diseases also have been additionally threatening the future of coral reefs� These multiple stressors may cause serious effects on the sustainability of coral-reef fisheries as the sources of income for small-scale fishermen all over Indonesia, who provide most of Indonesia’s food protein� In addition, many other ecosystem functions of coral reefs disappear or get worse, such as for coastal protection from erosion, habitat for spawning and nursery grounds of many valuable marine organisms, and source of medicine (Supriharyono 2000), as well as their use for marine ecotourism�

In response to these degraded coral-reef ecosystems, there have been significant efforts to introduce many different ways of rehabilitating the ecosystem by means of coral transplantation, artificial reefs, and Biorock� Many sunk reef structures made of concrete, shipwreck, old cars, and tires can sometimes function as artificial reefs, but become broken due to deterioration and wave action� Those structures that remain are usually dominated by algae, sponges, hydroids, soft corals, tunicates, and so on, while hard corals are rarely found to dominate (Goreau and Hilbertz 1996, 1998)�

One method that has been developed for more advanced coral-reef rehabilitation is the mineral accretion (Biorock) method� This technique works by electrolysis using low-voltage electric current Hilbertz 1979; (Hilbertz and Goreau 1999; Lee 1997; Van Treeck and Schuhmacher 1997)� Experiments by Hilbertz (1979) and Goreau and Hilbertz (Chapter 4) showed that minerals (mainly calcium carbonate or magnesium hydroxide) deposited on the substrate can grow up to 20 cm in two years, and corals transplanted onto them also grew faster; for example, Acropora cervicornis grew 5-8 cm in 10 weeks (Goreau and Hilbertz, Chapter 4)� An additional advantage of the Biorock approach is that transplanted corals can better tolerate relatively poor water quality�

The amount of mineral deposited onto the substrate depends on the current and voltage� High voltage and current result in faster mineral precipitation, but it is less hard because the deposited mineral is dominated by brucite (Mg(OH)2)� With lower voltage and current, the electrolysis process is slower, resulting in slower mineral precipitation on the cathodes, but it is harder because the dominant mineral is aragonite limestone (CaCO3)� These mineral deposits are similar to those being made by coral skeleton (Hilbertz and Goreau 1998)�

This research quantified the effect of different electric voltages on the growth and survival of various species of acroporid corals including Acropora nobilis, Acropora formosa, and Acropora valenciennesi (Wallace and Wolstenholme 1998) transplanted onto the Biorock structures at various places under different conditions� It is expected that this result will contribute in improving coral restoration, especially in specific areas where this technique is visible and strategic, such as close to resorts, hotels, or tourism sites�

METHODS

Study Sites

Studies to compare the growth rate of corals on the Biorock structures with genetically and environmentally identical controls not receiving electricity were conducted from 2002-2008 at several sites in Indonesia, including Pemuteran, Bali, the Spermonde Archipelago near Makassar,

Sulawesi, and Gili Trawangan, Lombok� The experiments were conducted at various depths on the reef flat or the reef slope� The following are the short descriptions of the main study sites:

Barrang Lompo Island

Barrang Lompo Island is a small, inhabited island around 15 km from Makassar city� The source of power was from a battery charger placed in a small house next to the beach� The Biorock structures were placed around 10 m from the house down to 4 m depth� The sea floor around this area is mainly soft sand and some seagrass and macroalgae� Coral reef patches develop only around 20 m from this site� The water transparency was relatively good in the study sites during this experiment�

Samalona Island

Samalona Island is a small, uninhabited island around eight km from Makassar city� The island has been a famous recreation destination, especially for local visitors� The Biorock structures were placed at around 5-9 m depth� The reefs around this island were in moderate condition with live coral cover around 30%� The water transparency was relatively good during dry season but becomes a bit turbid during rainy season, and it is affected by green water due to the proximity to Makassar, the largest city in Sulawesi�

Pemuteran Village

The location of this research site is in the Karang Lestari Reef Restoration Project in the Pemuteran Village Marine Protected Area, Gerokgak subdistrict, Buleleng Regency, Bali� The experimental units were placed around 4-6 m depth with relatively low visibility during the rainy season due to sediment runoff from the land�

Gili Trawangan

Details on the Gili Trawangan sites are provided in Arifin et al� (Chapter 6)�

MATERIALS

There were two main components of this experiment at Samalona and at Barrang Lompo: the power supply and the Biorock transplantation structure� Electricity on this island is supplied by gasoline power generator, which runs only during nighttime� Therefore, we used a charger with battery unit to supply power to the electrodes (Figure 5�1) during the day, whereas during the night, we used power adaptors to supply the electrodes with lower-voltage electricity from charged batteries� To test the effects of different voltages, we used 6 and 12 V batteries during nighttime� These power supplies were connected to the electrodes using cables� On Bali and on Gili Trawangan, the projects were powered for 24 h a day from shore-based chargers running at 12 V at the source, although the actual delivered voltage at the end of the cables is less�

The second main part of the experiment is the transplantation unit, which was made of a standard steel frame for coral (A. nobilis) transplantation (Figure 5�2)� The frame was made of reinforcing bar steel rods and wire mesh (cathode) on which the transplanted corals were attached, and the anode was positioned below the cathode (Figure 5�3)� Both the cathode and anode were connected to the power supplies placed on the land (Figure 5�4)� The coral fragments (around 10 cm) were attached to the cathode substrate using cable ties�

RESULTS

Barrang Lompo Experiment

Survival Rates

In general, both transplanted corals and those living in the vicinity (control corals) survived throughout the period of experiment (3 months)� However, there was a relatively low mortality (11%) on the 6 V treatment, due to external factors such as being eaten or removed by parrot fishes or entangled and removed by fish hooks� Therefore, this method at both voltage levels resulted in very good coral survival rates� The transplanted corals using this mineral-accretion method appear to survive better from algal overgrowth that usually invades transplanted corals, especially in a relatively low grazing level (Goreau and Hilbertz 1998; Jompa and McCook 2002a)�

Coral Growth Rates

The growth rates of minerals at Barrang Lompo are presented in Figure 5�5, and the coral growth rates of each treatment are presented in Figures 5�6 and 5�7� About three times faster growth of minerals was found on the higher voltage structure, which is due to the higher electrical current caused by Ohm’s law� The graphs show that all corals grew continuously� The total increase of coral length was measured every two weeks� Although there was a reduction of coral growth in the 6 V treatment, it was not due to the treatment but because some corals had their tips chewed off, possibly by parrot fishes� The average coral growth rates around 8 mm/2 weeks for 12 V treatment, 4 mm/2 weeks for 6 V, and 2 mm/2 weeks for control�

Coral transplants at this site without electrolysis had highest growth rates of 2�56 mm/2 weeks and lowest rate of 1�04 mm/2 weeks (Yuliantri et al� 2006)� This result is lower than transplants using the electrolysis method� It was interesting that the coral fragments bitten off by the fish recovered very quickly and started to grow faster again in the following weeks� This is in line with the experience of Goreau and Hilbertz (1996) that corals transplanted using the electrolysis method tend to develop faster with better reproduction and more resistance to the natural disturbances�

Statistical analyses showed that the treatment (different voltages) resulted in significant differences (P < �05) in coral growth rates� The t-test demonstrates that the 12 V treatment gave the highest coral growth rate, whereas coral growth between the 6 V was intermediate and the controls were lowest� The 6 V treatment was affected by mortality from fish biting during the eighth week� Therefore, the effect of this mineral accretion method at both voltages resulted in a much better performance in terms of better growth rates�

Samalona Experiments

The results of this experiment show that coral growth rate at 5 m depth with electric power is significantly higher compared to other treatments (Figures 5�8 and 5�9)� The electrified corals at

9 m depth were also significantly higher compared to those at nonelectrified corals (controls)� These data indicate that all electrified corals (5 and 9 m depth) grew significantly faster than the controls (Figure 5�10)�

Water Quality

The results of water quality measurements at all study sites showed that most of the parameters including temperature, pH, salinity, and water transparency were within a relatively normal range for seawater on coral reefs� Moreover, there were no significant fluctuations detected during study periods� Therefore, it can be assumed that the changes on coral growth rates observed here were mostly attributed to the effects of Biorock mechanism (Goreau and Hilbertz 1996)�

Pemuteran Experiment

The results from Pemuteran experiments, (Figure 5�11) show that both at 4 and 6 m depth, corals on Biorock grew four times faster than controls� At this site, no difference with depth was

observed for either electrified or control corals� We also observed that corals on electrical substrate had darker color, and new branches emerged more rapidly than on the controls� This indicated clearly that the electrified corals significantly benefited from the electrolytic process�

Gili Trawangan Experiments

Coral Growth

Coral growth was measured for different corals, staghorn and table Acropora species, at different sites and at different depths, and compared to growth of undisturbed natural reef colonies as well as transplants to substrates that were not electrified� All electrified corals grew much faster than controls, up to around eight times faster, and both electrified and control corals grew faster in shallower depths (Figures 5�12 through 5�14)�

Fish Populations

Fish populations were 6�25 times denser, 1�84 times more diverse, and 15�75 times more evenly distributed by species on Biorock structures than on surrounding natural reef areas (Figure 5�15)� The control area had 3�6 times greater dominance of the most abundant species than the Biorock reef�

DISCUSSION

The consistent results of all these different experiments conducted at different places and times under different conditions with different species strongly indicated that coral growth or coral skeleton deposition was significantly stimulated by low-voltage electricity using the Biorock method� These support the arguments and results previously described by Goreau and Hilbertz 1998� They suggested that increased pH around electrified cathodic frameworks resulting from electrolysis of seawater caused faster calcification and skeleton growth of electrically stimulated corals�

Another aspect that shows the well-being of electrified corals was their relatively high survival rates� The electrified structures not only provided the transplanted corals with better substrate to be strongly cemented onto but also increased the pH, which probably reduced the probability that the corals would be overgrown by macroalgae� Many species of macroalgae are detrimental to coral growth and survival, especially in areas of low herbivore and high nutrient levels (Jompa and McCook 2002b)�

It is interesting to notice that although Samalona and Pemuteran experiments used the same species (A. nobilis) and also similar electric voltage, the results showed different growth rates� The electrified corals at Samalona Islands grew at slower rate (0�2 cm/week) compared to those at Pemuteran (0�3 cm/week)� This could possibly be attributed to the different methods where the electrified corals in Pemuteran used a battery charger, while the source of the electricity at Samalona experiment came from a solar cell, which could be sometimes unstable due to cloud cover�

The fact that many Indonesian reefs (e�g�, in the Spermonde Archipelago) have been seriously degraded (Jompa 2007) makes it urgent to seek alternative solutions to restore coral reefs and fisheries habitat� The Biorock method appears to be especially relevant to the degraded reefs where natural recovery is unlikely to occur or very slow due to recruitment failure�

CONCLUSION AND RECOMMENDATION

Corals of different reef-building species were grown on electrically stimulated Biorock reefs at different locations in Southwest Sulawesi and Northwest Bali, Indonesia� All species of corals were found to grow significantly faster on Biorock at all sites than nearby controls� This increase ranged from (1) two to three times faster growth of A. nobilis at Biorock sites compared to controls in Southwest Sulawesi at different voltages, (2) two to four times faster growth of A. formosa on Biorock than controls at another Southwest Sulawesi site at depths of 5 and 9 m, (3) Up to 4�01 times faster growth for Biorock A. nobilis versus controls in Bali at 4 and 6 m depth, and (4) more than six times faster growth in Gili Trawangan� These results show clearly that coral growth rates can

be greatly increased with electrical trickle currents for habitat restoration� The responses appear to depend on species, local environmental conditions, and the amount of power received�

The Biorock method shows clear utility for restoring coral reefs and fisheries habitat in degraded reef areas� Therefore, this method could be used especially at those degraded reefs close to tourist destinations where electricity can be readily available� Because the specific benefits differ between species, location, and charging conditions, further work is needed to optimize the method for different species�

ACKNOWLEDGMENTS

We would like to thank very much Dr� Tom Goreau and Prof� Hilbertz for helping us applying the methods and providing us the anodes� Thanks also to the Center for Coral Reef Research at Hasanuddin University for the funding support� We also thank Agung Prana and the people of Pemuteran for their support to the Karang Lestari Project and the Gili Eco Trust for support to the Gili Trawangan projects�

REFERENCES