Feb 10, 2012 ... transects at Pulau Hantu and Sembawang Beach, the results ... temperature for
coral growth while temperatures at Pulau Hantu are optimal.
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.
