ABSTRACT

Coral reefs are biologically diverse ecosystems built by the accumulation of calcium carbonate (CaCO3) produced by reef-building Scleractinian corals and calcareous algae (Nybakken 1988)� Corals consist of two different groups, hermatypic (or reef building) with special symbiotic relationship between polyps and zooxanthellae dinoflagellates (Symbiodinium) (Veron 2000; Castro and Michael 2003)� Coral reefs serve as the venue for the cycle of biological, chemical, and physical as well as for wave-surge protection (Winarso et al� 1999)�

According to Suharsono (1998), the percentages that cover live coral of the western part of Indonesia is 3�93% excellent, 19�10% good, 28�09% fair, and 48�88% poor� The central part is 7�09% excellent, 22�70% good, 33�33% fair, and 36�88% poor� The eastern part is 9�80% excellent, 35�29% good, 25�49% fair, and 29�42% poor� There are five main threats leading to coral reef deterioration

CONTENTS

Introduction �������������������������������������������������������������������������������������������������������������������������������������� 81 Materials and Methods �������������������������������������������������������������������������������������������������������������������� 82

Study Area����������������������������������������������������������������������������������������������������������������������������������� 82 Environmental Parameters ���������������������������������������������������������������������������������������������������������� 83 Experimental Design ������������������������������������������������������������������������������������������������������������������� 83 In Situ Biological Observations��������������������������������������������������������������������������������������������������� 83 Data Analysis ������������������������������������������������������������������������������������������������������������������������������ 83

Environmental Parameters ����������������������������������������������������������������������������������������������������� 83 Survival Rate �������������������������������������������������������������������������������������������������������������������������� 83 Test of Significance ����������������������������������������������������������������������������������������������������������������84

Results and Discussion���������������������������������������������������������������������������������������������������������������������84 Environmental Parameters ����������������������������������������������������������������������������������������������������������84 Growth Rate and Branch Number of Coral Fragments �������������������������������������������������������������� 85 Survival Rate �������������������������������������������������������������������������������������������������������������������������������86

Conclusion ����������������������������������������������������������������������������������������������������������������������������������������88 References ����������������������������������������������������������������������������������������������������������������������������������������88

in Indonesia: (1) poison fishing: cyanide is squirted on coral heads not only to stun and capture live aquarium and food fish but also for killing the polyps; (2) blast fishing: small bombs are detonated in shallow reef areas, not only killing targeted schools of fish but also killing larvae, juveniles, and corals; (3) coral mining: corals are collected and smashed for house construction and live sale for the aquarium trade; (4) sedimentation and pollution from logging, erosion, untreated sewage, and industrial discharges, which kill the corals; and (5) overfishing, which does not destroy corals directly but reduces an abundance and diversity of fish and invertebrates (Tomascik et al� 1993)�

Because of its close proximity to Jakarta, a metropolitan city of about 12 million people, Seribu Islands Marine National Park serves as a holiday destination for people in Jakarta and vicinity (Fauzi and Buchary 2002)� The islands are subjected to considerable pressure from human use and pollution, which make the coral reefs in Seribu Islands increasingly vulnerable to domestic sewage, industrial wastes, and destructive fishing, including cyanide bombing and toxic materials (Bryant et al� 1998; Erdmann 1996)�

An artificial reef is one or more objects, natural or man-made, deployed purposefully on the seafloor to influence, physical, biological, or socioeconomic processes related to living marine resources� Artificial reefs are defined physically by the design and arrangement of materials according to their purpose (Bohnsack and Sutherland 1985; Carr and Hixon 1997; Seaman and Jensen 2000)�

The Biorock method, invented, developed, and patented by the late Prof� Wolf Hilbertz and Dr� Thomas J� Goreau, uses low-voltage direct current (between 1�2 and 12 V) to grow solid limestone minerals on conductive substrates� The minerals grown are naturally present in large amounts in seawater but do not crystallize by themselves� These current are safe to humans and all marine organisms� There is no limit in principle to the size and shape of Biorock structures�

Hard coral typically grow 2-6 times faster on Biorock structures than on controls (depending on species and conditions), show dense branching, have 16-50 times higher survival rates after severe high temperature stress, and show rates of new coral recruitment hundreds to thousands of times higher per unit area per unit time than recorded in the literature (Goreau 2008)�

The hypothesis of this study is that the Biorock process can increase the health, growth, and survival rates of hard corals and also can influence the growth forms of corals� The main purpose of this study was to (1) estimate the growth and survival rates of corals (Acropora sp�) on Biorock artificial structures, (2) compare them with survival and growth rates on the non-Biorock artificial reef, and (3) ascertain the effect of limestone deposited on corals’ growth morphology� The main aim of this study is to assess Biorock artificial reef as an alternative way for reef rehabilitation in Jakarta Bay by providing a natural limestone substrate produced in situ� This kind of artificial reef will be used for a variety of purposes, such as for aquaculture and breakwaters, to support conservation of biodiversity, to test ecological theories, to make available to the public as alternative diving sites, and may reduce human pressure on nearby natural reefs and therefore facilitate their rehabilitation�

MATERIALS AND METHODS

Study Area

This study was conducted for seven months (April through November 2009) as a field experiment at depth of −6 m at Pramuka Island in the Seribu Islands (Jakarta Bay, Indonesia)� The Seribu Islands (5°24′–5°45′ South, 106°25′–106°40′ East) are scattered around the northern part of the Jakarta Bay in the southwest Java Sea and consist of 78 small islands� Because of its close proximity to Jakarta, Indonesia’s major population center, the islands are subjected to considerable pressure from human use and pollution�

Environmental Parameters

The in situ environmental parameters measured monthly were temperature, pH, salinity, water current speed, and dissolved oxygen� Water samples were collected (underwater sampling at a depth of −6 m) from each study site� For long storage, water samples were preserved with 2 mL H2SO4/L and stored at 4°C (APHA 2005)� Other parameters measured in Proling Laboratory (Bogor Agricultural University, Faculty of Marine Science and Fisheries) were turbidity, total suspended solids (TSS), nitrate (NO3-N), and phosphate (PO4-P) using the nephelometric method, gravimetric method, colorimetric method, and ascorbic acid method, respectively (APHA 2005)� The purpose was to check whether the changes in growth and survival rates were due to the experimental treatment or changes in the environmental conditions�

Experimental Design

Biorock submerged structures were constructed from welded steel cathodes with a positively charged anode (titanium mesh)� A low electric direct current (3 V and 6 A) flows between them provided by a DC power supply� Calcium ions combine with carbonate ions and adhere to the structure (cathode), resulting in the growth of calcium carbonate over the steel� Coral fragments adhered to CaCO3 and grew quickly� Two species, namely, Acropora tenuis (branching) and A. cytherea (tabulate) were used for the experiment� Corals fragments collected from study area reef were cut as a thumb-sized tips and then attached to iron structures, both electrically charged Biorock structures, and identical uncharged control structures� Sixty coral fragments of each species were attached to the Biorock and control structures� The study was divided in two phases: the first phase of three months and then continued for the next 4 months (this is still in progress, to be published in details by Abdallah and coworkers) as the second phase�

In Situ Biological Observations

The submerged Biorock structures were observed every month; coral colony branch lengths were measured using a caliper with 0�05 mm scales, and other biological parameters were also noted� SCUBA diving gear and documentation equipment (writing board, underwater digital camera) were used (Figures 7�1 and 7�2)�

Data Analysis

Environmental Parameters

To test the significant effect on coral growth and branch numbers of the environmental parameters, analysis of covariance was computed using alpha 0�05 (Zar 1984), where the electrical current was the main variable, the environmental parameters were the covariates, and mean growth and increase of branch numbers were dependent variables�

Survival Rate

In biostatistics, survival rate is a part of survival analysis, indicating the percentage of samples in a study or treatment group that are alive at a given period of time� Survival rate in this study was determined by dividing the number of live coral colonies at the end of the study with the number of coral colonies at beginning of the study, multiplying by 100�

Test of Significance

To investigate the statistical significance of the difference between Biorock and control (μ1 and μ2), means of coral growth rates, increase in branch number rates, and survival rates (t-test) have been used (Kanji 2006)�

SPSS release 11�5�0 (September 6, 2002) and Microsoft Office Excel 2007 statistical software were used for collection, management, and analysis of the data� Textbooks were used for the identification of corals (Suharsono 1996; Veron 2000)�

RESULTS AND DISCUSSION

Environmental Parameters

In general, water quality at the study site was suitable for coral growth� Water temperatures ranged from 23-30°C, salinity 30-35‰, pH 7�6-8�3, turbidity 0�50-1�18 NTU, TSS 4-7 mg/L, dissolved oxygen 6�4-7�4 mg/L, current speed 0�05-0�09 m/S, PO4-P 0�02-0�09 mg/L, and NO3-N 0�002-0�022 mg/L�

Analysis of covariance on the effect of the environmental parameters showed that none of the environmental parameters had a significant effect on coral (A. tenuis and A. cytherea) growth rates or branch numbers� Differences in growth rates and branch numbers were due to the electricity�

Covariance analysis showed that there is no statistically significant effect of environmental parameters, and electricity (p = �548) helped in increasing the branch numbers of A. cytherea� This makes sense, because A. tenuis has three-dimensional open branching, while A. cytherea is tabulate and adds new polyps only at the periphery�

The deposition of minerals onto a cathode substrate through seawater electrolysis presumably enabled the increase in the concentration of mineral ions in a small boundary layer above the cathode that could be utilized by the coral for skeleton formation (Hilbertz and Goreau 1996)�

Growth Rate and Branch Number of Coral Fragments

By the end of the first three-month duration, our results estimated the mean growth rates for A. tenuis as 1�8 cm on Biorock and 2�4 cm on control, and for A. cytherea as 0�57 cm on Biorock and 0�74 cm on control, while for the second phase (next four months), the mean growth rates for A. tenuis were estimated as 5 cm on Biorock and 3 cm on control, and for A. cytherea as 1 cm on Biorock and 0�3 cm on control (Figure 7�3)�

The lower growth rates of fragments transplanted in Biorock structure compared with those transplanted in uncharged control structure (Figure 7�3a) was apparently due to the electrical power stability problem and irregular charging during the first three months, but when the power supply was stabilized during the second phase, this resulted in higher growth rates of corals transplanted on Biorock compared to controls (Figure 7�3b)� This could indicate that the main key for success of mineral-accretion artificial reefs is the electrical current stability� Electric fields allows accretion of carbonate because a low current causes elevation of pH in the immediate vicinity of the coral, increasing natural calcification, and from excess production and release of electrons, because the electrochemical processes at the cathode may affect the electron transport chain for ATP production, where excess energy can be used for growth promotion (Hilbertz and Goreau 1996; Sabater and Yap 2004; Schuhmacher et al� 2002; Tambutte et al� 1995, 1996)�

The growth rate reported in our study reflects a particular level of voltage and current (3 V and 6 A)� Growth rates may differ under different electrical regimes� Previous studies that used this method had voltages varying from 18 V and 4�16 A (Sabater and Yap 2002, 2004), 1 to 24 V (van Treeck and Schuhmacher 1997), 8 to 12 V (Schuhmacher and Schillak 1994), and 6 to 12 V (Hilbertz and Goreau 1996)� Our observations showed a large variation of increase of coral branches during two different phases� In the first phase, the mean increase in branches for A. tenuis was four branches on Biorock and three branches on control, and for A. cytherea it was six branches on Biorock and nine branches on control� During the second phase, the mean of increasing branch number for A. tenuis was eight branches on Biorock and five branches on control, and for A. cytherea it was 14 branches on Biorock and 11 branches on control (Figure 7�4)�

Fragments of corals transplanted on Biorock had unstable electrical power during the experimental first phase and this resulted in no significant difference in increasing branch numbers (Figure 7�4a), while during the second experimental phase with stable power, the coral fragments on the charged structure showed a significant increase in branch numbers compared with those transplanted on uncharged control structures (Figure 7�4b)�

Increasing pH in the vicinity of Biorock transplants may create a higher concentration gradient between the water outside the coral polyp and coelenteric cavity� This can lead to diffusional influx of mineral ions into the coelenteron via the “leaky” nature/permeability of cnidarian epithelium (Benazet-Tambutte et al� 1996; Tambutte et al� 1995, 1996)� This could increase the availability of ions for active uptake via transcellular route of calcification and would explain the significant increase in the number of branches and growth rates (Hilbertz and Goreau 1996)� The higher rates of increase in branch numbers than in the linear coral fragment growth implies that the coral’s tissue growth is benefitting more than the skeleton growth�

Survival Rate

Survival rate of corals reflects their ability to adapt/adjust to the new environment� All transplanted fragments were collected from around the experiment site and are influenced by transplantation techniques� Fragment size plays a role in transplantation success, where large fragments have a higher chance to survive more than small ones�

The data presented refer to survival rate as numbers of fragments found in original position and alive on the respective structures� Figure 7�5 shows the higher survival rates on Biorock (100%) than on control (73�3% and 83�3%) of the two transplanted corals species (A. tenuis and A. cytherea)� The difference between Biorock and control may be due to the influence of electrical field that inhibited the settlement of red filamentous and fleshy (Caulerpa racemosa and Padina sp�) algae� Losses were probably due to wave action, grazing activities, predation, and death caused by intrinsic factors�

We found some of the missing nubbins on the seabed close to the structures� Transplanted fragments were not all found dead on the structures but some of them disappeared due to wave action

or biogenic disturbances such as fish grazing� Van Treeck and Schuhmacher (1997) observed fishes (Labrids, e�g�, Thalassoma spp�, Cheilinus abudjubbe) moving some coral fragments while searching for invertebrates living in the skeletons of fresh fragments�

CONCLUSION

Electrical stimulation appeared to increase budding and branching of corals even faster than growth, suggesting that the positive effects of the electrical field on tissue-cell growth and division are greater than on the skeleton growth� The effects were greater on corals with three-dimensional branching than on table corals, where new polyps are limited to the periphery� By increasing the growth and survival rates of hard corals by stimulating coral branching and fragment length, Biorock reef restoration could be introduced as an alternative way for reef rehabilitation by providing a natural-like substrate with limestone character generated in situ, which will be useful for a wide variety of coastal management purposes�

REFERENCES

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