Longitudinal study of aspergillosis in sea fan corals

Aspergillosis (a fungal disease) is affecting sea fan corals Gorgonia spp. throughout the Caribbean. To measure the impact of this disease, we established longitudinal, or in other words individual-based, monitoring studies on 3 reefs in the Florida Keys, USA, to obtain estimates of incidence, rates of disease progress, recovery, and mortality. At Western Dry Rocks (near Key West), 40 Gorgonia ventalina colonies (20 initially healthy and 20 initially diseased) were photo-monitored between June 1996 and May 1998. Additional sea fans were visually monitored during 2 localized outbreaks at Conch (May 1998 to September 1999) and Carysfort (July 2000 to May 2001) reefs located in the Upper Keys. Data from Western Dry Rocks showed that over a 2 yr period, the incidence rate was 0.58 sea fans yr(-1) and that tissue purpling can lead to tissue loss and subsequently to mortality, albeit at low frequencies. Most sea fans, once infected, maintained a low level of damage over time. Only 3 fans recovered from the disease; however 2 were subsequently re-infected. Case fatality rate was 10% (2 of 20 initially infected died), which is equivalent to 5% yr(-1). However, mortality can increase during localized outbreaks. At Conch, mortality was 46% yr(-1) among infected sea fans (compared to 8% yr(-1) at Carysfort, a less impacted site, during the same period). During an outbreak at Carysfort, mortality was 95% yr(-1) among diseased sea fans. These data clearly demonstrate the significant role aspergillosis plays in the population ecology of sea fan corals.