Coral disease outbreak: pattern, prevalence and transmission in Acropora cervicornis

A rapidly progressing disease outbreak affecting Acropora cervicornis (staghorn coral) was recently observed over a wide geographic range (>200 km) in the Florida Keys, USA. Original observations made at White Bank Dry Rocks revealed colonies with tissue rapidly sloughing from multifocal lesions. Over the course of the epizootic at least 72 % of tagged colonies were affected, live tissue cover of these colonies decreased from 96 1 % to 12 5 % (mean SE), and 28 % of the colonies suffered complete mortality. Observed rates of tissue loss were highly variable, ranging from 2 to 43 cm(2) d(-1), but the mean was a rapid 13 +/- 11 cm(2) d(-1) or about 4 cm branch length d(-1). Field experiments demonstrate that this disease is transmissible not only by direct contact between affected and healthy staghorn coral tissue but also by the corallivorous snail Coralliophila abbreviata. The disease was also transmissible, although less effectively so, to the congener A. palmata (elkhorn coral). No transmission was observed in indirect contact treatments designed to simulate diver interaction. Transmissibility implies that the condition is indeed a biotic disease and the demonstration of effective vector transmission suggests that predation may exacerbate disease outbreaks in remnant Caribbean acroporid populations, further impeding their potential recovery.