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. The term 'soft' is a bit misleading because these corals have numerous tiny, needle-like spicules in their tissues.
Mushroom coral / Sarcophyton sp. / Family Alcyoniidae
Soft Coral / Dendrophthya sp. / Family Nephtheidae
Apart from their swaying bodies and jelly like feel, soft corals are distinguished by the eight tentacles on each polyp and have a feathery appearance, whereas hard corals have smooth tentacles.
Soft corals live on coral reefs along with hard corals.
Soft corals may seem potentially more vulnerable to predators than those which have a stony skeleton but, in reality, they are not. This is partly because of the presence of the spiky spicules, which function like thorns on a rose bush, and partly because 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.
Soft corals are able to 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.
Soft corals are much more likely to feed with their tentacles extended during the day than hard corals. Some contain zooxanthellae and appear brown in colour while the bright colour of the spicules are revealed in those without zooxanthellae. Only some species are able to retract their polyps. Some of these can also contract their entire structure when under stress such as in low tides.
Colourful 'soft' corals
Some corals produce hard skeletons but, because they have eight-tentacled polyps, are classified as soft corals. Another peculiarity of these species is the bright colour of the skeleton that remains after their death.
Blue coral, which can form massive colonies, owes its colour to iron salts. It grows in warm water north of Ingham.
Organ pipe coral skeleton is red, but is obscured by polyps that feed much of the time. The tube-like skeleton resembles organ pipes and is actually composed of fused spicules, not solid limestone as in true hard corals.
Sea pens are quill-like soft corals that inhabit soft sandy bottoms. A primary polyp anchors the animal in the sand and secondary polyps branch out from it.
Humans can damage corals by hitting them with anchors, walking on them and polluting the water they live in. Storms can injure or even kill many corals. Diseases can also kill them.
Protecting soft corals
It is important to treat corals well so they can be around for a very long time. Never remove or break off a piece of coral. When reef walking, never walk where you are not supposed to and stick to the sandy areas. When you are in a boat never anchor near a coral reef because the anchor could get caught in the coral and destroy it.