Coral Reefs of Singapore
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|The coral reefs in Singapore are found skirting many of the islands south of mainland Singapore. These comprise fringing and patch reefs. See coral cover by island.|
St. John's Island
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 (Chou 2006, 2008).
The high turbidity
of our waters restrict light penetration and reef life ends at a depth
of only 12m, marking the lower growth limit for hermatypic corals. Sedimentation
rates ranged from 3-6mg/sq-cm/day in 1979. In 1994, these increased to 5-45mg/sq-cm/day
(the higher value obtained from localised areas close to reclamation projects).
This reduced visibility from 10m in
the 1960s to 2m or less today. As a consequence, the reef is very compact,
as opposed to reefs in clear waters, which can be found at depths of 20m
on our reefs
The reef can be subdivided into several zones: the reef flat, the reef crest and the reef slope. The shoreline gives way to the shallow reef flat that may vary in width and depth - at very low tides, some parts of the reef flat are exposed to air and direct sunlight. Here, scattered about are small colonies of boulder-shaped knob corals (Favia), maze coral (Platygyra sp.) and sponges of different colours. Pockets of sandy areas may be surrounded by lawns of large brown algae Sargassum sp. Bands of black sea urchins gather in large numbers. This level also marks the outer edge of the reef flat, which gives way to the reef crest.
Marine life on the reef crest is usually the richest - almost every type of coral is represented: the brain corals (Family Mussidae), bubble-corals (Family Caryophyllidae), pore corals (Family Poritidae), mushroom corals (Family Fungidae), cauliflower coral (Pocillopora sp), cave corals and disc coral (Family Dendrophyllidae), the table and staghorn corals (Acropora sp.), anemone corals (Goniopora sp)and many others. Living among these corals are many other marine animals. Deep purple-coloured sea anemones, with their symbiotic clownfish are a common sight. Crinoids (feather stars) are cryptic by day, and hide in coral crevices. Attached on the reef substrata are the sponges, sea squirts (tunicates), feather-duster worms and stinging hydroids. The other more mobile reef residents are the cowries, cone shells, nudibranchs, shrimps and crabs may be found in the crevices of the reef.
No other marine habitat supports such numbers or diversity of fishes as coral reefs. Most reef fishes adopt bright colouration, curious body shapes and habits. They not only add much vibrancy to the reef, but also are important contributors in almost all levels of the coral reef ecosystem. The most diverse and abundant fishes in Singapore reefs are the damselfishes (Family Pomacentridae) and wrasses (Family Labridae). Other common reef fishes are the copperband butterflyfish (Chelomon rostratus) and vermiculated angelfish (Chaetodontoplus mesoleucus). Some of the reef fishes are economically important as food fish. These include the groupers (Family Serranidae), snappers (Family Lutjanidae), scads and trevallies (Family Carangidae).
As the upper reef slope gives way to the lower reef slope at about 7 to 8m depth, the density of marine organisms decreases. Coral boulders are scattered, separated by coral rubble, sand and silt. Occasionally, one comes across some sea urchins, crinoids, gobies, goatfishes and mushroom corals, the Neptune-cup sponges and brilliantly coloured sea-fans.
The sea floor of
many reefs in Singapore is usually silty. Long sea whips and smaller sea
fans are common. A few isolated colonies of corals still grow at these
depths, but most of these are ahermatypic (do not possess symbiotic zooxanthellae),
and hence able to colonise the darker parts of the reef.
to Singapore reefs
Acknowledgements: Many thanks to Ria Tan for help with web design and photos, Jeffrey Low, who helped with initial design, plus past and present members of the Reef Ecology Study Team.