Don,

A dense population of Neopetrosia subtriangularis also appeared suddenly
at a shallow site (coral reef grading into seagrass, on a slope) in
Bocas del Toro, Panama some years ago, and then a few years later
vanished all at once. I wasn't there when the mortality occurred so I
don't know that every individual perished at once as at Ramrod Key, but
they certainly all vanished during a 6-month period between my visits.
My hunch is that it is an abiotic factor, because disease tends to move
through a population more slowly, with portions of some individuals
sporting lesions at [...]