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. outbreaks of rapid tissue loss diseases, or “white diseases” (bythell et al. 2004), have caused significant coral mortality in recent decades and have contributed to the extraordinary loss of living coral cover documented on shallow reefs in the caribbean (aronson and precht 2006). These diseases have included white band disease and white band disease type ii on acropora spp. and white plague types i, ii, and iii on multiple caribbean coral species not of the genus acropora (sutherland et al. 2004). all of these syndromes present as a distinct line of tissue loss that originates basally or peripherally on an affected colony and progresses rapidly (although rates differ depending on the disease), leaving behind areas of freshly denuded skeleton that appear bright white (reviewed by bythell et al. 2004). causal agents have been identified for white plague type ii (richardson et al. 1998b, Denner et al. 2003) and white band type ii (kline and Vollmer 2011), but these pathogens have not appeared in corals with similar disease signs in other parts of the caribbean, suggesting that the same disease signs may represent multiple etiologies (pantos et al. 2003, pollock et al. 2011). reports of white disease and other disease outbreaks in reef-building corals have increased dramatically over the last few decades (weil et al. 2006), though it is unclear whether this is representative of true increases in disease incidence or is the coRAl Reef pApeR