If you know where to look, you can actually discover some quite fascinating aspects of the marine ecosystems in the waters around Singapore.

Did you know that there are about a hundred-and-eighty species of hard coral in Singapore's waters, which is more than at Pulau Tioman or Hawaii?

Hard corals form the main components of the reef ecosystem. Reefs are structures made of calcium carbonate, derived from the exoskeletons of animals called polyps. A coral consists of a thin layer of living tissue covering the hard skeleton. Each polyp has a mouth which is surrounded by tentacles which trap food particles.

The reefs in Singapore's waters are mainly fringing reefs, which means that they are connected to the shoreline, as opposed to being separated by a lagoon. These reefs are located around the southern islands such as Pulau Semakau.

In addition, there are patch reefs, which are not connected to any visible landmass but are exposed at low tide. An example of a patch reef is the Cyrene Reef.

Sadly, the land reclamation programme of the mid-sixties saw about sixty percent of good fringing reefs on the west, southwest and southeast coasts being obliterated.

The sandy beaches stretching from Changi to the Kallang Basin have been reclaimed. The reefs of Pulau Sudong, Pulau Hantu, Kusu Island and the Ayer Chawan group of islands have also been affected by reclamation. Visibility underwater is now less than two metres on a clear day, compared to as far as ten metres in the early sixties.

Reclamation is significant because it results in turbid sea water. This in turn reduces light penetration, inhibiting plankton growth. The coral polyps feed on the plankton.

Other environmental conditions are more favourable to coral growth. For example, sea surface temperatures around the Southern Islands range between 27 oC and 31 oC throughout the year, and pH lies between 8.0 and 8.2 (Chou, 1986).

Wherever they may be found, Singapore's fringing and patch reefs share certain similar characteristics. The intertidal reef flat, regardless of its width, has a gentle gradient of around 1:600. It is exposed to varying amounts during low tide.

About five to ten metres before the sudden plunge of the reef slope is the reef crest, where coral cover is very dense. It is in this area, together with the upper five metres or so of the reef slope, where vigorous growth and a healthy species diversity are still maintained.

The reef slope itself can be almost vertical and levels off to a sandy bottom at a depth of between fourteen to thirty metres, where sunlight can no longer penetrate because of the turbid water. In fact, according to Chuang (1977), at a depth of fourteen metres, ninety-nine percent of surface light is blocked off, resulting in a light intensity there of only two hundred lux. It is here that the leathery, white, soft corals are found.

Part 2: Why are corals found on reef slopes rather than reef flats?

Part 3: What is the government doing to protect our coral reefs?

Reproduced with permission from the site formerly known as 'No Place Like Home', © Kenneth Y T Lim 1995-9