What coral disease creates a bright white ring of exposed skeleton, often fatal?

The coral disease that creates a bright white ring of exposed skeleton and is often fatal is white plague disease.

White plague is a tissue-loss disease of stony corals. Its characteristic lesion is a sharp boundary between living, pigmented tissue and freshly exposed white skeleton. In an annular form, the lesion can look like a bright ring spreading across the colony as coral tissue dies and recedes. The exposed skeleton may later become covered by algae or sediment.

The disease was first reported in the Florida Keys in 1977. Researchers have described several forms, including types I, II, and III, which differ mainly in how quickly tissue loss progresses. White plague can affect many species of scleractinian, or hard, corals and has caused extensive mortality during Caribbean outbreaks.

It is commonly confused with white band disease, which primarily affects Caribbean acroporid corals such as elkhorn and staghorn corals. Stony coral tissue loss disease can also resemble white plague and was initially described in some reports as a white-plague-like syndrome, but it is treated as a distinct disease complex.