Preliminary Investigation on the factors
affecting the growth of coral reefs in
Singapore
Matthew Cho Lai Liang
Benjamin Chew Xuan Zheng
Tan Shi Qi
Yishun Junior College
Little Green Dot Student Research Grant
PROJECT REPORT
submitted to
Nature Society (Singapore)
Junior College Category 2011
3041 words
ABSTRACT
This project aims to investigate the effects of two factors, temperature and the
concentration of dissolved oxygen, on the growth of coral reefs in Singapore.
Coral reefs provide many benefits to coastal cities like Singapore for reasons
like the protection of coastal regions or to boost tourism. Thus it will be
beneficial to investigate the factors that might affect coral growth. Through
experiments conducted with the dissolved oxygen probe with the help of grid
transects at Pulau Hantu and Sembawang Beach, the results collected showed
that there are greater fluctuations in dissolved oxygen concentrations between
the two sites as compared to temperature readings. Temperatures taken at the
Sembawang region are also more constant and higher than the optimal
temperature for coral growth while temperatures at Pulau Hantu are optimal.
Further analysis done concluded that in this study, the effects of temperature
may be more significant than concentration of dissolved oxygen. However, this
experiment is unable to deduce if other factors affect growth of corals. Thus for
further investigation, the scope of this project could be increased to encompass
a greater study on other factors that affect the growth of coral reefs so as to
complete the picture of coral growth in Singapore.
INTRODUCTION
In recent years, many factors have led to the endangerment of coral reefs both
locally and abroad. Coral reefs bring about a great span of benefits. Coral reefs
serve not only to beautify one's country's landscape; it also provides natural
protection of the coast by serving as a natural barrier protecting beaches or
coastal cities such as Singapore from the effects of wave erosion (Coral Reef
Alliance, 2010). Most of all, it would provide an environment to trap sand and
other sediments, therefore widening our coasts.
Furthermore, they have medicinal value and are used to treat many illnesses
and diseases such as cancer and cardiovascular diseases (WWF, 2011). In
addition, coral reefs help in the carbon fixation process to absorb greenhouse
gases and this helps in mediating global warming (O'Dea. A, 2010). Fixation of
carbon dioxide by the algae causes an increase in the concentration of
carbonate ions in the cells of the coral polyp, leading to fluid of cells being more
alkaline.
Coral reefs are also home to thousands of fish species (Coral Reef Alliance,
2010) and this biodiversity translates directly into food security, income, and a
multitude of other benefits to people in the form of tourism dollars for Singapore.
Although Singapore is not well known for her coral reefs currently, this option
can be explored in the future. Hence, maintaining the growth of coral reefs is
important. This however, is seen to be a difficult task as reports have shown
that many reefs in Southeast Asia are now threatened or even endangered. The
Bleach Watch Singapore (Bleach Water Singapore, 2010) organisation has
stated “Most corals around Singapore were in danger because of sediment
released during land reclamation work”.
Based on current studies into the growth of coral reefs, the known factors that
would perturb the healthy growth of coral reefs are namely temperature, pH,
dissolved oxygen, light transmission, sedimentation, salinity and lastly, turbidity
(Cutler. J, 2010). Firstly, temperature is seen as a key factor. Coral reefs, like
enzymes, are unable to withstand high temperatures and at high temperatures,
corals will bleach and this will threaten the survival of the coral reefs from the
entire region. Therefore, when there is an anomaly in sea surface water
temperature, the extent of coral bleaching is huge. This was seen in Singapore
during the 1998 coral bleaching event whereby an increase in 1 to 2°C in the
sea temperatures around Pulau Hantu and St John's islands affected 50-90% of
all reef organisms in Singapore (Reef Ecology Study Team, 2010). The effects
of temperature were supported by more evidence when 10 out of 35 coral
colonies died from the stress during a study, with the genera Sinularia and
Euphyllia being most affected (Reef Ecology Study Team, 2010).
Secondly, coral reefs are affected by concentration of dissolved oxygen as
coral reefs are marine animals which require oxygen to respire. Low oxygen
levels might also lead to high bacterial concentrations which will affect growth of
coral reefs (Falkowski, 1984). According to the Jaubert Method,
chemoautotrophic bacterial growth will occur in the absence of oxygen. This will
affect the growth of coral reefs as there is a higher chance that the bacteria will
infect the corals and the coral reefs will die off massively. Studies also show
that at least two groups of bacteria are consistently associated with astreoides
against a complex microbial background, indicating that it may impact coral
reefs’ health and survival (Falkowski, 1984).
However, as there is not much study on the effects of concentration of
dissolved oxygen on growth of coral reefs in Singapore, we feel that such a
study would prove to be useful. Thus our project focused on investigating the
concentration of dissolved oxygen and temperature in two coastal regions of
Singapore to determine if these two factors will affect the distribution of coral
reefs in Singapore.
METHODOLOGY & MATERIALS
Two sites were chosen to contrast between areas where more coral reefs
can be found (Pulau Hantu) and areas where not many coral reefs can be found
(Sembawang Park). As seen from Figure 1.1, Pulau Hantu has a high
distribution of patch reefs in islands south of mainland Singapore; hence, we
decided to choose this to represent the site for high number of coral reefs and
Sembawang Park, where the pollution level of seawater is high (STOMP, 2009),
to represent the site for low or no presence of coral reefs. The blue section
represents coral reefs distribution.
Figure 1.1 shows the distribution of coral reefs around islands south of mainland Singapore, which
comprise fringing and patch reefs. (Reef Ecology Study Team, NUS. (n.d.). Coral reefs of Singapore.
Retrieved from http://coralreef.nus.edu.sg/)
If any significant differences in concentration of dissolved oxygen or
temperature were observed between the two sites, it may suggest the level of
importance of that factor in sustaining the healthy growth of coral reefs.
A twelve metre by twelve metre grid transect was used to locate the points for
the taking of readings (Fig1.2). This grid transect can be formed by using raffia
strings and a frame which is the outer border of the grid transect. For Pulau
Hantu, 4 sets of readings are obtained with each set taken at 4 metre intervals
from 4 metre to 12 metre while for Sembawang beach, four sets of readings are
obtained per transect with each set taken at four metres. Due to safety reasons,
each set was taken at 4 metre only in Sembawang beach. Transects were
deployed from 3 random sites each at Pulau Hantu (Fig 1.3) and Sembawang
beach.
As seen in Fig 1.2, the intersection point of the string is where we take our
readings. Under each intersection point of the grid transect, the dissolved
oxygen probe was lowered to a fixed depth of one metre to measure for the
concentration of dissolved oxygen in the sea water and the sea surface water
temperature (refer to Fig 1.3).
1 set 4m Dry Land 8m
12m Fig 1.2 shows the intersection points of the grid transect placed at position where seawater touches dry
land.
The four green dots represent one set of data collected at a specific distance
from shore.
Fig 1.3 shows the locations of transects laid out in the coastal region of Pulau Hantu.
Fig 1.4 is a diagrammatic representation of the grid transect
Fig 1.4 is a cross sectional view of the grid transects that were constructed. It
is made up of different coloured strings which were four metres in length each.
The purpose for the different coloured strings is to easily identify the points to
take readings. The spots that the readings were taken are shown by the yellow
dots and at the intersection between the different coloured strings, a knot was
tied to make it easier to attach the probe sensor.
RESULTS
The data collected are presented in the tables below.
Table 1: Readings obtained at Sembawang beach
Site Sets
no.
1
1
2
3
4
2
1
2
3
4
3
1
2
3
4
Distance from
shore/m
4
4
4
4
4
4
4
4
4
4
4
4
Temperature/°C
30.3
30.3
30.2
31.0
30.2
30.1
30.3
30.2
30.2
30.3
30.5
30.5
% of dissolved oxygen
concentration
74.2
74.7
75.5
77.3
80.1
80.7
81.0
81.8
71.6
74.3
74.8
75.3
Table 2: Readings obtained at Pulau Hantu
Site Sets
no.
1
1
2
3
4
2
1
2
3
4
Distance from
shore/m
4
8
12
4
8
12
4
8
12
4
8
12
4
8
12
4
8
12
4
8
12
4
8
Temperature/°C
28.9
28.6
28.5
28.5
28.5
28.5
28.4
28.5
28.6
28.3
28.6
28.6
28.5
28.5
28.7
28.7
30.4
29.5
29.5
29.3
29.3
29.6
29.6
% of dissolved oxygen
concentration
76.1
68.6
74.0
68.3
73.8
74.5
82.2
77.1
75.6
85.1
82.1
75.4
80.2
79.5
77.0
93.2
86.1
88.3
84.6
85.3
83.7
92.5
84.6
3
12
4
8
12
4
8
12
4
8
12
4
8
12
1
2
3
4
29.4
29.8
29.9
29.3
29.4
29.4
29.3
29.4
29.4
29.4
29.5
29.4
29.4
86.2
93.2
88.8
84.3
80.4
76.9
74.6
82.8
77.7
76.4
79.6
78.2
61.8
Table 3: Comparison of temperature readings of seawater between Pulau
Hantu
and Sembawang Beach
Site
no.
Distance from
shore/m
Temperature of the
waters in
Pulau Hantu/°C
Temperature of the
waters in
Sembawang/°C
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
4
4
4
4
4
4
4
4
28.9
28.5
28.4
28.3
28.5
28.7
29.5
29.6
29.8
29.4
29.4
29.5
30.3
30.3
30.2
31.0
30.2
30.1
30.3
30.2
30.2
30.3
30.5
30.5
Table 4: Comparison of concentration of dissolved oxygen in seawater
between Pulau Hantu and Sembawang Beach
Site
no.
Distance from
shore/m
% of dissolved oxygen
concentration
Pulau Hantu
% of dissolved oxygen
concentration
Sembawang
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
4
4
4
4
4
4
4
4
76.1
68.3
82.2
85.1
80.2
93.2
84.6
92.5
93.2
80.4
82.8
79.6
74.2
74.7
75.5
77.3
80.1
80.7
81.0
81.8
71.6
74.3
74.8
75.3
DISCUSSION
Based on Table 3, the temperature of the seawater at Pulau Hantu, which
range from 28.3°C to 29.8°C, is lower than that of Sembawang Beach, which
range from 30.1°C to 31.0°C. This indicates that the temperature of the
seawater may be a contributing factor to the growth of coral reefs in Singapore.
This can be supported research that has shown that photosynthesis pathways
in zooxanthallae are impaired at temperatures above 30°C, this effect could
activate the disassociation of coral / algal symbiosis (Jason Buchheim, 1998).
Hence, it proves that no coral reefs can survive above temperatures of 30°C
and above and the optimum temperature range from 28°C to 29°C.
Another difference found in this investigation is dissolved oxygen concentration.
As shown in Table 4, there are fluctuations in the dissolved oxygen
concentration for both sites, especially the readings for Pulau Hantu. However,
the dissolved oxygen concentration of Pulau Hantu is relatively higher than that
of Sembawang Beach. This shows that dissolved oxygen concentration may
affect the growth of coral reefs but not to a large extent.
AVERAGE
STDEV
88.16666667
5.352631751
T-test
0.002048362
Based on the t-test value, it is less than 0.05 which is the significance level. This
implies that there is significant difference in concentration of dissolved oxygen
and hence, we can suggest that dissolved oxygen might be a factor that will
affect the growth of coral reefs.
According to research, the loss of oxygen affects the respiration of fish and
bottom-dwelling animals that cannot survive when levels of dissolved oxygen
drop below two to five parts per million. When this occurs, aquatic organisms
die in large numbers, which leads to a decrease in animal and plant diversity
and a disruption in the food chain. Once the herbivorous fish that kept harmful
algae in check are eliminated, algae will overgrow and smother the coral reefs.
(John Gary Recyclers, 2011)
This is a preliminary analysis based on the limited data collected. More data
needs to be collected from different parts of Singapore in order to conduct a
more accurate analysis.
From the data collected, it already can be seen that temperature seems to
affect growth of coral reefs. On the other hand, there is insufficient data from
our study to show that dissolved oxygen levels affect coral growth.
Other factors may contribute to the growth of coral reefs. One possible factor
that can be investigated further is light transmission in Singapore waters. When
proper environmental conditions are present, such as good lighting conditions,
corals thrive and multiply naturally. Light transmission affects photosynthetic
rates of the Zooxanthellae, indirectly impacting coral growth and survival.
Studies have found that the sun provides up to 95 percent of a coral’s daily
energy budget. [Falkowski, 1984]
Although the differences of concentration of dissolved oxygen in seawaters
might not be sufficient to tell us that it is the main contributing factor that will
affect growth of coral reefs, the fact that coral reefs grow in shallow waters
suggests that high light transmission may ensure the healthy growth of coral
reefs.
Another factor that can be further investigated is the salinity of the sea waters.
High salinity will reduce the percentage of light transmission to coral reefs and
this will indirectly hinder coral reef growth and may lead to coral bleaching.
[Jordan West, 2011] Thus it will be invaluable to determine if the salinity of
waters in Singapore can affect the coral reef distribution as well.
Another key factor that can be investigated in Singapore will be sedimentation
as it is identified as one of the key contributing factors that reduce coral growth.
Sedimentation reduces available light for coral growth, inhibiting photosynthesis
by symbiotic algae. Sedimentation can cause coral bleaching as particles that
settle on coral surfaces interfere with photosynthesis and feeding. The coral
reefs of Singapore suffer from heavy sedimentation, the result of extensive
reclamation of Singapore’s coastline. A number of islands which include Pulau
Hantu have been reclaimed which will affect the growth of coral reefs. Thus, it
will be an interesting study to investigate the level of sedimentation at the sites
surveyed in this project to find out if temperature or sedimentation plays a
bigger role.
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ACKNOWLEDGMENTS
Our group would like to thank Madam Tay Woon Ping for guiding us
along our project as well as to get the permit to Pulau Hantu to conduct
our field work. Secondly, we would like to thank Mr Chua Chee Siang,
who aided us in our data collection by joining us for our field work.
Thirdly, I would like to thank Lim Xin Yi, an ex-student of Madam Tay, for
sharing some of her tips and experiences for our fieldwork. Next, I would
like to thank Yishun Junior College’s Laboratory Technicians for being
there and providing us with the laboratory equipment for the recalibration
of the dissolved oxygen probe. Lastly, I would like to thank Nature
Society (Singapore) for giving us this opportunity to gain enriching
experience during the process of our project. Without all the respective
people or organisation stated above, we would not have completed this
project successfully.