coral reefs Singapore’s reefs fringe the Southern Islands and consist of almost 200 species of hard coral. Dr John Crawfurd described the beauty of these islands in 1830: ‘We made an excursion yesterday to some coral banks lying among the islands which form the western boundary of the harbour of Singapore. These banks exhibit the strangest and most fantastic forms of organic life that can be imagined, in the various shapes of corallines, madrepores (both corals), asteria (starfish) and sponges. In still deeper water, and off the southern extremity of the island, there are found those gigantic sponges, which are peculiar to the coast of Singapore, and which Europeans have called Neptunian Cups’.
From the 19th century, these reefs were exploited for building materials, based on the evidence of coral fragments retrieved from archaeological excavations. These were probably from reefs fringing the mainland between the Singapore River and Tuas. This early exploitation, and development until the 1960s, did not contribute heavily to reef degradation.
However, this changed from the 1970s, as development accelerated sharply. Land reclamation buried close to 60 per cent of Singapore’s reefs, including those along the mainland coast. Reefs that escaped reclamation were subjected to the impact of heavy sedimentation resulting from reclamation, dredging of shipping channels and dumping of dredged spoils. Average underwater visibility was reduced from 10 m in the 1960s to 1 m in the early 21st century. Sedimentation retards coral growth by smothering and reducing sunlight penetration. Since the 1970s, sedimentation resulted in the loss of coral from below 6 m of the reef slope, and an average 34 per cent reduction in live coral cover from the upper slope.
Further pressure was added by the collection of reef animals for the aquarium trade, which started in the 1960s. Public concern was expressed in the media in the late 1970s when it became known that Korean construction workers were collecting large quantities of coral from the reefs and shipping them home, where the specimens fetched high prices. Harvesting of corals and reef animals decreased when Singapore ratified the Convention on International Trade of Endangered Species, but the damage was evident from the drop in the numbers of many reef species, particularly fishes.
Reefs along Singapore’s mainland coast have been totally eliminated, except for a small reef community at Labrador. There are some reef communities in the northeast islands of Pulau Tekong and Pulau Ubin (see Chek Jawa). However, most of Singapore’s reefs fringe the Southern Islands. Although the abundance of many species has been depressed, species’ elimination is not evident. Of the 200 species of hard coral recorded in these reefs, only two have been confirmed as lost. Other reef- associated animals, such as seashells, giant clams, sea cucumbers and sea stars, are also less common due to habitat loss, degradation and earlier unregulated exploitation.
Singapore’s reefs have become dominated by foliose growth forms (flowery corals), which have a large surface area with which to capture the reduced sunlight energy. Branching Acropora coral, which dominates other reefs in the region, is now uncommon in Singapore. However, Singapore’s reefs have been spared the coral- eating crown- of- thorns starfish. It is not known why this starfish has not established itself in Singapore, when outbreaks have occurred on reefs in nearby Bintan and Tioman.
In September 1997, a collision between the Eviokos and the Orapin Global, two tankers, resulted in the spillage of 28,000 tons of crude oil. This threatened the marine environment, but had little impact on the reefs as containment measures diverted the slick. However, in early 1998, elevated sea temperature resulted in mass bleaching of Singapore’s corals on a scale previously unknown. More than 90 per cent of all corals were bleached, and 20 per cent failed to recover after the sea temperature returned to normal.
Reef development and growth depends on successful spawning, and the availability of a suitable substrate for larval settlement and growth. Mass spawning, where many coral species release eggs and sperm or fertilized egg bundles, takes place over a few nights during the full moon in March or April. This major event is followed by a smaller one in September or October. These spawning events coincide with the inter- monsoon lull.
Photo credit: Chou Loke Ming