In our previous article on Corals of Sydney I discussed hard corals or Scleractinia. In this article I’ll describe the soft corals, or octocorals. These are colonial animals with eight tentacles on the polyps, typically growing on a soft rather than hard skeleton.
Soft corals have a lot in common with hard corals – they both have stinging polyps which want to get up into the water column to feed – but in the case of soft corals they build flexible structures rather than hard calcareous ones. Some soft corals use a hydraulic system, inflating when the currents are strong enough to feed.
Other soft corals build a more rigid structure, often using material like our fingernails.
Carijoa, a very successful genus around the world, common in Sydney at places like Shiprock, goes one further and enjoys a symbiotic relationship with an orange sponge which coats and protects the central structure on which the polyps grow: