A couple of neon green Psammocora have just been discovered to be living unattached, as free living coral colonies known as ‘rolloliths’. Psammocora is just the latest stony coral genus to be documented living as a rollolith, a growth form in which a colonial stony coral is completely covered in tissue, with no point of attachment present.
There are plenty of corals that live unattached and free living on the reef, but these species are specially adapted to this lifestyle with a clearly defined ‘top’ and ‘bottom’ surface. This is why it is such an anomaly to find colonial corals with a rounded shape, more or less living as rolling coral tumbleweeds.
The two latest entries to the Rollolith logbook appear to be Psammocora superficialis, a stout species of stony coral which is better known as an encrusting colony that is often endowed with pretty colors and colorful edges or mouths. The two specimens revealed by Cairns Marine were collected at a small reef approximately 20 nautical miles east of Mourilyan, Queensland which is just to the south of Cairns.
The sweetest thing about encountering corals as rolloliths is that we tend to think of corals as delicate little flower animals which should never be touched.
Certainly these corals would appreciate a more stable lifestyle, attached to the reef and being able to settle into a more permanent situation. Yet these newest colonies among many others prove that corals are very durable, and can even withstand living as a rock, tumbling among coral rubble and being none the worse for wear.