Gorgonia ventalina builds a lattice of branches that fuse into a broad flat mesh supported by a flexible core of gorgonin, a horny protein, stiffened with calcareous spicules. Because there are no algae doing photosynthesis in the way reef-building corals rely on, the colony's food comes from suspended particles.
Catching those requires flow. Repeated observations across Caribbean reefs show fans aligned with the plane of the colony roughly perpendicular to the dominant current or surge direction, presenting the greatest area to the passing water. Polyps extend from both faces, so water passing through the mesh is filtered on both sides. The flexible skeleton lets the whole structure bend in surge instead of snapping.
Sea fans have their own disease history. An outbreak of aspergillosis caused by the fungus Aspergillus sydowii damaged Caribbean sea fan populations from the 1990s, producing characteristic purple lesions. The common misreading of a sea fan is that it is a plant or seaweed. It is a colony of octocoral polyps, and its shape is a feeding structure.