A flat purple fan of fused branches, set across the prevailing current so the whole colony filters it. Look on it for flamingo tongues.
Colonies to about 1.5 or 1.8 m tall. A single flat fan of fine interconnecting lattice built on several main branches. Whitish, yellow or pale purple, and the main branches are often distinctly purple. The fan sits at right angles to the prevailing current, which is a good thing to notice underwater.
The Venus sea fan is the confusion, and the difference is in the small branches: in this species they are round in section or flattened in the plane of the fan; in the Venus sea fan they are flattened at right angles to the plane, and it also carries short stubby side branches sticking out of the plane, giving it an untidier look. In the Bahamas the two are easy to tell apart. In Florida and the Lesser Antilles they are much harder.
It carries symbiotic algae and also feeds on plankton carried past by the current, so it lives on shallow high-energy fore-reef and reef crest between about 1 and 30 m.
It is the classic host of sea fan aspergillosis, caused by a soil fungus washed off the land, which produces purpling, galls and lesions and drove large Caribbean die-offs from the 1990s. Severity tracks low salinity and runoff.
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.
