FACT SHEET 16
SOFT CORAL
• Soft corals are soft bodies made up of a large number of polyps connected by fleshy tissue. They lack the limestone skeleton found on their relatives, the hard coral. Instead they contain minute, spiney skeletal elements called sclerites. Aside from their scientific utility in species identification, sclerites give these corals some degree of support and give their flesh a spiky, grainy texture that deters predators.
• 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.
• 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 corals contain powerful toxins (terpenes). Underwater, these toxins make the tissues of soft corals either distasteful or toxic to fish. They are also put to use in the constant battle for space. Soft corals introduce them into the water around them where they can kill neighbouring hard corals and repel other soft corals, sponges and algae which might otherwise grow too close or over the top of the soft coral.
• Soft corals move, very slowly, by extending the tissues at their base. When their route crosses hard coral colonies they kill the polyps, leaving a white, dead path behind them.
• Like hard corals, most soft coral species contain small single-celled algae (zooxanthellae) that live inside their tissues. They provide a very significant source of nutrition by leaking energy rich sugars into their hosts. Most species are also able to feed on small plankton in the water. Unlike hard corals, most soft corals thrive in nutrient-rich waters with less light intensity.
• Soft corals grow relatively quickly and can double or triple the size of their colonies over a year. They clone themselves repeatedly until a large colony of identical polyps has been formed. They also reproduce by spawning their eggs and sperm up into the water column. In Australia, soft corals on the Great Barrier Reef do all of this in the big mass spawning event that occurs on the Great Barrier Reef each year. The larva of a soft coral looks almost identical to that of a hard coral and is also called a planula. The larvae of soft Coral remain in the water column for 5-10 days before settling down on
the bottom of the sea and forming a new colony. They find the right spot by light and chemical (smell) clues.
• 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.
• Reef Check Australia identify and monitor soft coral. We record the following types of soft coral; Leathery Soft Coral (SCL), Zoanthids (SCZ) and Bleached Soft Coral (SCB).
Interesting Fact: The potential exists for soft corals to be a source for useful chemicals, such as antibiotics or other drugs.
Further Links:
• Wikipedia: http://en.wikipedia.org/wiki/File:Soft2.jpg
• ReefEd: http://www.reefed.edu.au/home/explorer/animals/marine_invertebrates/corals_and_jellyfish/soft_corals
• CRC Reef Research Centre: http://www.reef.crc.org.au/discover/coralreefs/softcoral.html
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