Like bizarre lifeforms from another planet, our soft corals may look like flamboyant bushes or giant leathery disks.
A soft coral is generally a colony of countless tiny animals called polyps linked to one another. Soft corals can look like branching bushes or trees. They may also be flatter and look like mushrooms or even fried eggs! When exposed at low tide, they often flop over and look like a pile of jelly. When submerged, however, they expand into beautiful plant-like forms and some appear 'furry' as the tiny polyps expand.
Soft corals are identified by polyps that have 8 (or multiple of 8) tentacles that are pinnate (branched or feathery). (Hard corals have polyps with 6 or multiples of 6 tentacles that are unbranched). This unidentified soft coral shows clearly these features of the polyp. Although there are exceptions, many soft corals don't produce a hard skeleton. Instead the polyps are connected by a soft tissue mass.
Leathery corals are commonly seen on our Southern shores and in some places can grow quite large! But they all are made up of tiny polyps. The different kinds and arrangements of polyps help to identify them.When the colony is out of water, the polyps retract completely into the shared tissue so that the entire colony appears smooth and leathery.
When submerged, with the polyps expanded, the colony can appear rather 'furry' and may be mistaken for sea anemones.
Some look like a pile of discarded rubber gloves! The entire colony can be quite stiff. So please do not bend leathery corals or handle them roughly. Some may tear, while others contain dangerous toxins.
Some leathery corals form small disks with really short polyps.
Soft flowery bushes
Some soft corals look like colourful bushes, but they are actually animals!Again, each is a colony of tiny polyps.They come in different colours.
'Hard' soft corals
Sea fans are considered soft corals because their polyps have 8 (or multiples of 8) tentacles that are branched.The polyps are linked one another and supported by a central rod made of a tough but flexible protein called gorgonin that is similar to the material produced in the horns of animals.Some colonies take on branching forms, but the branching is only along one plane (most are not bushy). These colonies are usually called sea fans. Others are unbranched and grow into one long whip-like form, and are called sea whips.All kinds of small animals live on gorgonians including tunicates, barnacles, clams, tiny shrimps, crabs, brittle stars and gobies.
Tiny brittle stars have wrapped their arms around these sea fans.This pink flowery soft coral had tiny porcelain crabs and a spotted snail on it.Some of these small animals prey on the sea fan, such as these Ovulid snails. These animals usually take on the shape and colour of their host.
More confusing soft corals
Blue corals (Heliopora coerulea) are confusing.
Firstly, they are often brown and don't appear blue at all. Secondly, although they have a hard skeleton, they are not grouped with other hard corals and are considered soft corals!They are grouped with soft corals because their tiny polyps have 8 tentacles with fine branches like other soft corals.
Their internal skeletons are blue, hence their common name. The blue colour is due to the iron salts that are incorporated into their skeletons. On the outside, they are usually brown because the thin layer of living tissue that covers the outer surface of the skeleton is brownish.
Blue corals are considered living relicts of fossil species known from more than 100 million years ago. Most other corals have an evolutionary age of only several hundred thousand years. Blue corals used to be dominant before the last Ice Age when the seas were warmer. They are now only found in warm tropical waters.
Links to more
Photos of soft corals and sea fans of Singapore on wildsingapore flickr