Brown band disease (BrB) primarily affecting acroporids, particularly thicket-forming species such as Acropora formosa, A. aspera, A. acuminata and A. intermedia. BrB also affects pocilloporids and faviids less frequently.
BrB consists of dense aggregations of mobile ciliates located between living tissue and exposed coral skeleton. These appear to directly consume coral tissue; endosymbiotic zooxanthellae (Symbiodinium) are generally visible within the ciliates and give the band its characteristic brownish color.
BrB manifests as a golden-brown band, 0.1-1 cm wide, with a slight jelly-like consistency. As the disease progresses, a band of white skeleton is visible behind the band which is rapidly colonized by algae (usually within one week).
Often, a narrow band of white skeleton is also visible at the advancing front of the disease, separating the ciliates and healthy coral tissue.
In branching species, the band typically circumscribes the branch. The disease usually begins at the base of a branch, rapidly progressing upward. There is usually only a single band per branch. Multiple branches may be affected on individual colonies.
On tabular and massive species, the band generally begins at the colony margin, and progresses upward and inward.