Corals are marine organisms from the class Anthozoa and exist as small sea
anemone-like polyps, typically in colonies of many identical individuals. The
group includes the important reef builders that are found in tropical oceans,
which secrete calcium carbonate to form a hard skeleton (Darwin,
1889). The development of these structures is aided by algae that are symbiotic
with reef-building corals, known as zooxanthellae. The reef is topographically
complex and because of that, thousands of species of fish and invertebrates
live in association with reefs, which are by far the richest marine habitats
In recent days, coral reefs are under threat from the climate change and ocean
acidification. However, human activities may represent the greatest threat to
coral reefs. Pollution especially agricultural runoff, over-fishing, blast fishing
and the digging of canals threaten reefs by reducing the water quality. Experts
have found a new way to save and to restore the population of coral reef by
creating high-quality artificial habitat for marine organisms and helps jump-start
the establishment of coral community (Goreau and Hilbertz,
2005). The solution is to develop artificial reefs made from certain substances
such as concrete and ceramic.
An Artificial Reef (AR) is a structure that is deliberately or accidentally
introduced to the seabed and is performing the function of attracting marine
life. The creation of manmade structures to enhance marine resources is the
basis of a specialized branch of marine technology known as artificial
reef development and is widely considered as a tool for protecting the
natural ecosystem and enhancing fisheries production. An AR provides shelter
from predation and surfaces for larvae to settle on; the organisms that are
attracted create new food sources and attract other species, thus a matured
AR site (3-5 years) may also play a role in increasing biodiversity in and around
the AR site (Goldberg, 1973). Coastal communities in
some countries have traditionally used ARs to increase their catches. They are
now established with the involvement of governments, the private sector and
NGOs for various reasons, using a diverse range of materials from disused oilrigs,
ships, vehicles and railway tracks, to purpose made concrete blocks and bamboo
structures. AR construction has different purposes in different countries, for
example, in the United States ARs are constructed mainly to improve recreational
fisheries; in Japan, to benefit commercial fisheries; and in some European countries,
to control inshore trawling and to increase fish production for rural fishing
communities (Wilkinson, 2008).
Artificial reefs have potentials as a positive management tool that can be
used to allow the stressed natural site to recover and to develop a new habitat
on the seafloor for reef creatures like corals, fishes and other marine invertebrates.
One of the high priorities of marine organisms is a safe sanctuary and artificial
reef offers many hiding places from the surroundings and once corals are present
its even better (Clark and Edwards, 1999). Hard coral
is the core of a coral reefs ecosystem; therefore a restoration structure has
to promote coral growth in an area where it would otherwise not occur (Clark
and Edwards, 1999).
Upon considering the importance of artificial coral reef ecosystem, present study was conducted to determine the propagation and biodiversity of corals on artificial reefs at Teluk Kalong and Pasir Akar, Malaysia.
MATERIALS AND METHODS
Study area: This study was carried out at Redang Island which is located 45 km off the coast of Kuala Terengganu, Malaysia. Two locations were chosen as the study area since the artificial reefs were deployed there (Fig. 1). The first location is Pasir Akar (Lat: 5.75°, Long: 103°) which is situated approximately 3 km off from the jetty and submerged at 15 m of depth. In this area, around 15 units of Dome Reefs and 70 units of EnviroReefs were deployed. The second location was Teluk Kalong (Lat: 5.7666667°, Long: 103.0166667°) which was about 1 km off from the jetty. The water was shallower with mean depth of about 5 m. In this area, a total of 15 units of Dome Reefs, 56 units of EnviroReefs and 10 units of Cheese Reefs were deployed.
These artificial reefs were developed by the Dorken Company. Dome Reef was
built mainly from concrete. It has holes that not only go into the module but
also between the walls. The large open area in the center was designed to provide
fish shelter. EnviroReef was made from ceramic with selective mixture of oxide
minerals which naturally occurred in the environment. It was built to mimic
branching corals which increases it stability (Fig. 2a, b).
|| Location of the study area
||(a) Dome Reef structure and (b) EnviroReef structure were
deployed at the sampling stations
The sampling was carried out at two different stations during a sunny day (between
9 am to 3 pm). This period received optimum sunlight and provided the best visibility
to identify the corals, capture pictures and record data. Ambient environmental
parameters such as temperature, conductivity, total suspended solid, salinity,
dissolved oxygen, pH and turbidity of the study area were measured using a multiprobe
parameter. The sampling process was carried out by capturing photo and video
recording using underwater camera. Underwater slate was used to record data
such as characteristic (e.g., shape, colour, size etc.) and identified using
standard reference (Humann and De Loach, 2002). These
data were obtained after several diving at the sampling sites during 2009. Collected
data were analyzed using Shannon Wiever Diversity Index and Pielou Evenness
Coral distribution on artificial reefs at Teluk Kalong and Pasir Akar:
Based on the observations, coral distribution on artificial reefs at Teluk Kalong
was relatively low (Table 1). In the EnviroReefs structure,
Seriatopora hystrix was the only coral growth observed. 40% of the reefs
surface was occupied by Seriatopora hystrix on the dome reefs structure,
followed with Macrodactyla doreensis. Pasir Akar had recruited greater
abundance and diversity of corals compared to Teluk Kalong (Table
2). In this area, 3 species were identified on EnviroReefs structure. However,
Seriatopora hystrix was still the dominant species with other coral species
such as Favia stelligera and Platygyra sinensis were growing on
certain part of the branching structures. Interestingly, on the dome reefs 8
species were identified with Oulophyllia crispa being the most abundant
Index analysis: In general, the diversity index of both locations was relatively low. The Shannon diversity index of corals at Teluk Kalong and Pasir Akar was 0.6425 and 1.7410, respectively. The Pielou Evenness Index of Teluk Kalong and Pasir Akar was 0.1766 and 0.3247, respectively.
Diversity of corals on different reef structure: The Shannon diversity index of corals on EnviroReefs and dome reef structures were 0.5359 and 2.2192, respectively while the evenness index showed the value of 0.1284 and 0.4247, respectively (Table 3). Overall, the diversity index showed that the diversity of corals on dome reefs was higher than the EnviroReefs structure.
|| The abundance and diversity of corals samples at Teluk Kalong
|| The abundance and diversity of corals samples at Pasir Akar
||Species diversity and evenness index of corals observed on
selected artificial reef structures
Coral distribution on artificial reefs: The low abundance and diversity of corals on artificial reefs at Teluk Kalong might be due to the fact that the area had no natural coral reefs which could propagate the coral larval to initiate the restoration process. The location itself was situated only 1km away from the jetty where it was exposed to the daily movement of tourist boats and fishing ships. As a result, water turbidity of this area might act as a limiting factor on the coral propagation. These factors made the establishment of coral community in that area becomes a time-consuming process. Existing natural coral reef ecosystem would provide the home to various coral species that ultimately result in coral larvae to spread along the surrounding environment at Pasir Akar. Moreover, it is also a protected area where human influence is strictly restricted. Therefore the natural habitat is conserved with suitable water quality. This condition provides a suitable environment that promotes a better growth of coral colonies in this area.
Corals diversity and distribution on dome reefs were higher than on EnviroReefs structure. This might be due to the structure of EnviroReefs which has branching-like arrangement which is more suitable in recruiting branching coral such as Seriatopora hystrix. It was also observed that dome reef provided a more stable medium for the recruitment of slow-growing corals such as Oulophyllia crispa. Most of them grew on the wall of the dome reefs which provided a large amount of surface area for the attachment.
The installation of artificial reefs was expected to foster the creation of
new suitable and stable surfaces in order to assist coral recruitment (Abelson,
2006; Walsh, 1985). Artificial reefs at Teluk Kalong
and Pasir Akar were designed to restore natural coral reefs community. Both
EnviroReefs and dome reefs were designed to mimic the natural reefs in order
to meet the ecological needs of corals and fishes in this area.
EnviroReefs were designed with a structure similar to the branching corals.
Small reef fish inhabits in EnviroReefs installations naturally keep algal and
soft coral overgrowth under control, creating favorable conditions for rapid
coral colonization. The modules in these Reefs have features to help facilitate
the successful settlement of microscopic coral larvae, including fluted surfaces
to generate turbulence and a microporous surface texture for improved coral
adhesion. In addition, when installed in large, close-packed arrays of modules,
the turbulence generated by the module branches slows water flow over the site,
stabilizing sediment and creating conditions conducive for fish nursery area
Dome reefs had been engineered to withstand against sea forces (chemical and
physical) and shaped with ecological uses. Ecologically, dome reefs were built
to optimize protective void spaces for fishes and include features such as rough
surface textures to enhance coral settlement. Holes were designed to create
whirlpools that help bring nutrients to corals and animals living on the dome
reefs surface. Therefore, dome reefs were an excellent shelter and feeding area
of fishes and other coral related organisms (Han et al.,
1994; McGurrin et al., 1989).
In conclusion, diversity indices showed that Pasir Akar had better coral establishment when compared with Teluk Kalong. It was also clear that dome reefs were better in promoting the propagation of coral communities in this area. However, when comparing the two types of artificial reef structures in term of ecological role in restoring the coral reefs ecosystem it was proven that both were efficient in providing a medium for coral establishment as well as other coral associated organisms.
The authors are grateful to Dorken Reef Corporation Sdn. Bhd. No. 33B, Jalan SG 3/19, Pusat Bandar Taman Sri Gombak, 68100 Batu Caves, Selangor for sponsoring the sampling session at Pulau Redang Island.