One of a Kind: The Coral That Doesn't Need Sunlight

If you have ever dived beneath a reef overhang or looked closely at a shaded reef wall, you may have come across a brightly coloured coral growing where very little light reaches.

At first glance, this seems unusual. Most people associate corals with clear tropical water and bright sunlight, so finding a coral thriving in caves, beneath ledges, or on steep reef walls naturally raises a question: how does it survive with so little light?

For carnation corals the answer is surprisingly simple. Unlike many corals, sunlight is not their primary source of energy.

Carnation corals belong to the genus Dendronephthya, a group of soft corals found throughout the Indo-Pacific region.

Unlike hard corals, they do not build large limestone skeletons. Instead, they form colourful, tree-like colonies that can appear red, pink, orange, yellow, or purple. Their bright colours often make them stand out against the reef, particularly when large colonies are growing together.

At first glance, they can look more like underwater flowers than corals, which is where their common name comes from.

Most reef-building corals live alongside microscopic algae that provide energy through photosynthesis. This partnership allows corals to make use of sunlight and is one of the reasons many reefs are found in clear, shallow water.

Carnation corals have taken a different approach. They do not depend on photosynthetic algae and instead obtain all of their food directly from the water around them. Tiny plankton and other suspended particles drifting past become their primary source of energy, allowing them to live successfully in habitats where light is limited but food carried by currents remains abundant.

This makes carnation corals an example of non-photosynthetic corals, often shortened to NPS corals.

Their shape reflects this lifestyle. Each colony is covered in hundreds of tiny feeding structures that extend into the water, increasing the chances of intercepting passing food. Strong currents continuously deliver plankton and other suspended particles, providing the constant supply of food these corals require.

This dependence on water movement explains why carnation corals are often found on exposed reef slopes, vertical walls, beneath overhangs, and in deeper habitats where food-rich currents are common.

One of the most striking things about these corals is that the vibrant reds, oranges, pinks, and yellows we associate with them are not produced by photosynthetic algae. Even without relying on sunlight for energy, carnation corals remain some of the most colourful organisms found on a reef.