Common Sea Fan

• The whole colony orients itself like a sail to maximise the flow of water through it, which is why the fans in any one area all face the same way.
• It hosts symbiotic algae in its tissues, just as the hard corals do, and it too bleaches when the water warms.
• Since the 1990s it has suffered outbreaks of aspergillosis caused by a fungus of terrestrial origin that reaches the sea in runoff, and which has decimated whole populations in the Caribbean.
• Its fan always grows in a single plane, oriented at right angles to the current, so that water passes through it and the polyps catch the plankton it carries.
• The skeleton is made of gorgonin, a flexible protein, and not of rigid carbonate: that is why it bends with the swell instead of snapping.
• Since the 1980s it has suffered epidemics of aspergillosis, caused by a soil fungus, Aspergillus sydowii, which reaches the sea in dust and run-off and has killed sea fans across the Caribbean.
• It defends itself against the fungus with an immune response of its own: it walls the infection off in melanin nodules, and the colonies that survive show greater activity in that pathway.
• It is the visual emblem of Caribbean reefs, and the purple colour comes from pigments in the skeleton itself.

Habitat & environment

Reefs and rocky bottoms of the Caribbean, from 2 to 30 m

Sources consulted: Linneo (1758); Smith et al. (1996), Nature; Mydlarz et al.; Smithsonian Marine Station