coral reef
Tuesday, 6. May 2008, 07:07:48
Depleting coral reef off Singapore shore
Introduction
Southeast Asia is undergoing rapid economic and population growth. Many Southeast Asians are economically dependent on the sea and the coral reefs. The seas are being polluted by organic and inorganic wastes from sewage, from agricultural and industrial wastes, and from run-off containing oil, hydrocarbons, and heavy metals. All of these contribute to sediment run-off and increased turbidity. Siltation of coral regions is also caused by excessive deforestation and land clearing for commercial crops. Construction and land reclamation has caused changes in water circulation and has increased sedimentation. On the coral reefs, there has been extensive overexploitation of resources by heavy fishing pressure, including very destructive methods such as blasting, coral mining, and cyanide poisoning for live fish collection.
Coral Reefs in Singapore
There were once over 60 offshore islands and patch reefs around Singapore, most of which were situated south of mainland Singapore. However, since the mid 1970s, major land reclamation was carried out on the mainland as well as the offshore southern islands. Most of the southern islands were reclaimed, adding 1695 ha to Singapore's total land area. Some islands were merged as a result. The reef flats of many islands e.g. Pulau Sudong, Pulau Hantu and Kusu Island were reclaimed right up to the reef slope. Many of the coral reef organisms were smothered by the reclamation, while others were severely affected by the resulting increase in water turbidity. Since 1986, most coral reefs in Singapore have lost up to 65% of their live coral cover.
Threats to Singapore reefs
The most significant cause of reef degradation in Singapore is sedimentation. Land reclamation, dredging of shipping channels and dumping of earth spoils, have increased the sediment load. Loss of coral reefs to land reclamation occurred along the southwest coast of the mainland and on some of the offshore southern islands. Increased sedimentation affected the remaining reefs in two ways
1) By causing a slow but steady reduction in live coral cover
2) By reducing the lower depth limit of coral growth on reef slopes.
Surveys since 1986 indicated that live coral cover decreased by up to 20% on some reefs, although other reefs registered no impact. The reduction in sunlight penetration reduced the lower depth limit of coral growth. In the 1970s, coral growth extended to 10m down the reef slope. Today, growth is restricted to 6m although some coral species still occur at the 8m depth.
Accidental oil spills remain as an ever-present threat. However the 1997 Evoikos oil spill (27,000 tonnes) did not seriously affect coral reefs, although oil contaminated the upper parts of some reef flats.
Other activities that also have an impact on the reefs include recreational and tourist-related use. Negligent or inexperienced divers without proper buoyancy control, leave a trail of broken corals. Anchor damage is caused by fishing boats and pleasure craft. At Pulau Hantu, a popular dive spot, courtesy mooring buoys were previously installed to prevent anchor damage.
As with coral reefs around the world, Singapore reefs suffered a mass bleaching event in June 1998. Sea temperatures around Pulau Hantu and St John's were elevated by 1-2 deg C from March to June 1998. 50-90% of all reef organisms in Singapore were affected, particularly the hard corals, soft corals and anemones. The bleaching effect extended till 6m, the lower growth depth limit for coral growth locally. Sea temperatures returned to normal in August 1998.
Introduction
Southeast Asia is undergoing rapid economic and population growth. Many Southeast Asians are economically dependent on the sea and the coral reefs. The seas are being polluted by organic and inorganic wastes from sewage, from agricultural and industrial wastes, and from run-off containing oil, hydrocarbons, and heavy metals. All of these contribute to sediment run-off and increased turbidity. Siltation of coral regions is also caused by excessive deforestation and land clearing for commercial crops. Construction and land reclamation has caused changes in water circulation and has increased sedimentation. On the coral reefs, there has been extensive overexploitation of resources by heavy fishing pressure, including very destructive methods such as blasting, coral mining, and cyanide poisoning for live fish collection.
Coral Reefs in Singapore
There were once over 60 offshore islands and patch reefs around Singapore, most of which were situated south of mainland Singapore. However, since the mid 1970s, major land reclamation was carried out on the mainland as well as the offshore southern islands. Most of the southern islands were reclaimed, adding 1695 ha to Singapore's total land area. Some islands were merged as a result. The reef flats of many islands e.g. Pulau Sudong, Pulau Hantu and Kusu Island were reclaimed right up to the reef slope. Many of the coral reef organisms were smothered by the reclamation, while others were severely affected by the resulting increase in water turbidity. Since 1986, most coral reefs in Singapore have lost up to 65% of their live coral cover.
Threats to Singapore reefs
The most significant cause of reef degradation in Singapore is sedimentation. Land reclamation, dredging of shipping channels and dumping of earth spoils, have increased the sediment load. Loss of coral reefs to land reclamation occurred along the southwest coast of the mainland and on some of the offshore southern islands. Increased sedimentation affected the remaining reefs in two ways
1) By causing a slow but steady reduction in live coral cover
2) By reducing the lower depth limit of coral growth on reef slopes.
Surveys since 1986 indicated that live coral cover decreased by up to 20% on some reefs, although other reefs registered no impact. The reduction in sunlight penetration reduced the lower depth limit of coral growth. In the 1970s, coral growth extended to 10m down the reef slope. Today, growth is restricted to 6m although some coral species still occur at the 8m depth.
Accidental oil spills remain as an ever-present threat. However the 1997 Evoikos oil spill (27,000 tonnes) did not seriously affect coral reefs, although oil contaminated the upper parts of some reef flats.
Other activities that also have an impact on the reefs include recreational and tourist-related use. Negligent or inexperienced divers without proper buoyancy control, leave a trail of broken corals. Anchor damage is caused by fishing boats and pleasure craft. At Pulau Hantu, a popular dive spot, courtesy mooring buoys were previously installed to prevent anchor damage.
As with coral reefs around the world, Singapore reefs suffered a mass bleaching event in June 1998. Sea temperatures around Pulau Hantu and St John's were elevated by 1-2 deg C from March to June 1998. 50-90% of all reef organisms in Singapore were affected, particularly the hard corals, soft corals and anemones. The bleaching effect extended till 6m, the lower growth depth limit for coral growth locally. Sea temperatures returned to normal in August 1998.
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