Dynamics of an Acute Coral Disease Outbreak Associated with the Macroalgae Dictyota spp. in Dry Tortugas National Park, Florida, USA

Reports of coral disease outbreaks have increased in recent decades, but often few details are known about these outbreaks, such as environmental triggers, associated biological variables, or even the precise temporal span of the outbreak. Here we document an acute outbreak of a rapid tissue loss disease on the highest live coral cover (15%–30%) reefs within Dry Tortugas National Park, Florida, USA. This disease exhibited similar signs to white plague disease with the notable exception that a white film often was observed on the recently denuded skeleton. The temporal span of the disease was short (<2 mo). Partial mortality was recorded but there was no detectable impact to overall coral cover. A significant increase and then decrease in the cover of macroalgae, primarily of the genus Dictyota, occurred simultaneously with the increase and drop in disease lesion density (number of lesions per living tissue area), respectively. No other anomalous biological or physical factors (e.g., unusual temperature, turbidity, passage of storms) corresponded with the outbreak, although it is likely that some environmental anomaly that was undetectable with the methods employed favored both disease and Dictyota expansion. This is the first study to associate a rapid increase in a macroalgal population with a coral disease outbreak. We highlight the need for increased study of the initiation of such outbreaks in the caribbean.