What are Corals?

Found in warm, shallow seas across tropical and subtropical regions, corals are living animals that build some of the most diverse ecosystems on Earth. Although they may look like rocks or plants, each coral is made up of hundreds, sometimes thousands, of tiny animals called coral polyps. These polyps are distant relatives of jellyfish and sea anemones. Each has a simple body, with a mouth surrounded by tentacles that help it capture food from the water.

Every polyp lives within a hard skeleton made of calcium carbonate. Through a process known as calcification, corals take in dissolved minerals from seawater and slowly build these rock-like structures beneath their bodies. Over time, as polyps grow, divide, and remain connected to one another, they form large colonies. These colonies gradually create the complex, three-dimensional structures we know as coral reefs.

Corals are active feeders. Their tentacles are equipped with tiny stinging cells that allow them to catch plankton and other small organisms. However, much of their energy comes from a close partnership with microscopic algae, known as zooxanthellae, which live inside their tissues. These algae use sunlight to produce sugars through photosynthesis, providing food for the coral. In return, the coral gives the algae nutrients and a protected place to live. This mutually beneficial exchange is known as symbiosis. This relationship also gives many corals their vibrant colours. When corals are stressed by heat, pollution, or other changing conditions, they may expel these algae and turn white, a process known as coral bleaching.

A wide variety of marine life depends on coral reefs. Fish, crabs, shrimps, molluscs, worms, sponges, and countless other organisms use reefs as places to feed, hide, breed, and grow. Although coral reefs cover less than one percent of the ocean floor, they support around a quarter of all marine species. This makes them one of the most biodiverse habitats in the world.

Coral reefs are also important for people living along the coast. Their hard, layered structures help reduce the force of waves before they reach the shore, protecting coastal areas from erosion, flooding, storms, and other forms of damage. In Southeast Asia, where many communities live close to the sea, reefs can act as a first line of defence against increasingly unpredictable coastal conditions.

Beyond their ecological role, coral reefs also support human livelihoods and ways of life. They provide food and income through fishing, attract visitors through diving and tourism, and contribute to scientific and medical research. For many coastal communities, reefs are also tied to local knowledge, memory, stories, and everyday practices at sea. In this sense, coral reefs are not only natural habitats, but also living cultural landscapes.

Common Coral Species

Coral reefs in Singapore and the Riau Archipelago, including Bintan, are home to a wide variety of coral species. While many of the same coral genera can be found across both regions, differences in water clarity, sedimentation, coastal development, and reef conditions shape which corals are most common in each place.

There are a few simple ways to recognise common corals. One is through their growth form, or the shape in which they grow. Some corals form branching structures (branching corals), others grow as large rounded boulders (massive corals), while others spread out in thin plates, leafy layers (plating corals), or even live as single, free-living individuals on the seabed. Together, these different coral forms create the structure of the reef, offering shelter, surfaces, and feeding grounds for a wide range of marine life.

In Singapore’s reefs, commonly recorded coral genera include Goniopora, Merulina, Pachyseris, and Pectinia. Long-term studies have also shown that Merulina, Pectinia, Montipora, and Pachyseris are among the dominant genera on Singapore’s shallow reefs. In Bintan, clearer waters in some reef areas support a greater presence of branching corals, including Acropora, which are often less dominant in Singapore’s more turbid and sedimented waters. In Singapore, due to pressures of coastal urbanization, Stylophora, has become a critically endangered genus, while Seriatopora hystrix has even become locally extinct.