Aspergillosis is a condition that affects branching gorgonians and sea fans. The disease causes tissue loss and breakdown of the proteinaceous skeleton, resulting in small lesions distributed throughout the sea fan blade. The lesions may progressively increase in size, and eventually kill the colony, leaving behind the central axis of the colony.

The disease is characterised by irregular lesion(s) of various sizes distributed throughout the sea fan blade; loss of tissue and skeleton. Tissue surrounding the lesion often becomes dark purple. Identification of this disease requires confirmation of the presence of white fungal filaments. Sea fans may also have nodules.

This condition is caused by a soil fungus Aspergillus sydowii that may have been introduced into the marine environment in runoff or during dust storms originating in Africa.

Tissue adjacent to the infection often becomes a dark purple, due to an increase in skeletal structures known as sclerites. This purpling also occurs in response to other irritations, including predation, abrasion, and other diseases, and is not a definitive sign of aspergillosis.