The polyps open and close continuously, and nobody has settled why.
A soft coral forming low clusters of stalks each topped with a crown of feathery polyps, usually cream, grey-brown or pale blue. It carries symbiotic algae and gets most of its energy from them.
Its distinguishing feature is motion: the polyps open and close in a slow continuous pulse, each crown independently, and a colony in good condition never stops. The function is disputed — proposals include improving the exchange of oxygen and carbon dioxide around the algae, and sweeping food towards the polyps — and none is settled. It is fast-growing and can carpet dead substrate. The Xenia swimming crab and the eastern triangular butterflyfish both depend on it, and it is worth checking a colony for the crab before moving on. Recorded from about 2 to 25 m.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
