Soft Corals

Soft coral showing sclerites in white tissues. Photo: V. Harriott

While soft corals contribute in only a small way to the formation of the limestone structure of the reef, they play an important role in reef ecology. They are also a beautiful, diverse and colourful element of the reefscape.

Soft corals, along with hard corals, are in the Phylum Cnidaria, having in common a very simple body plan and polyp structure.

Soft coral is the common name for a group with the scientific name Alcyonacea. The soft corals can be distinguished from the hard corals by the fact that soft coral polyps always have eight tentacles, while hard coral polyps have multiples of six tentacles.

Researcher examines soft coral beds. Photo: K. Fabricius

Most soft corals also lack a hard external skeleton, although a few species, such as the red organ-pie coral (Tubipora) and the blue coral (Heliopora) have a skeleton that differs from that in a hard coral. In the shallow waters of the tropical Indo-Pacific, there are 90 genera of soft corals. In many parts of the world, the soft coral group is the dominant element of the coral reef landscape.

Despite their lack of reef-building capacity, soft corals form an important part of the coral ecosystem. They occur commonly in all reef habitats. They display a dazzling array of colours, including bright yellows, red, oranges and purples, and a wide range of colony shapes.

Soft coral tissue contains small hard sclerites. These can strengthen the base of the soft coral and are used by scientists to assist in the identification of the soft coral species.

Like hard corals, most soft coral species contain small single-celled algae (zooxanthellae) that live inside their tissues. The algae transfer food to the host coral. Most species are also able to feed on small plankton in the water.

Gorgonian corals are soft corals commonly found on drop-offs Photo: CRC Reef

Many soft corals exude mucus with traces of chemicals that repel other organisms such as sponges and algae, which might otherwise growth too close or over the top of the soft coral. The potential exists for soft corals to be a source for useful chemicals, such as antibiotics or other drugs.

For more information on identification and distribution of soft corals on the Great Barrier Reef, go to the soft coral atlas.

Ecology and biochemistry of soft corals