| Aspergillosis is a disease caused by the fungus Aspergillus sydowii which affects a number of shallow-water octocorals including the common Caribbean sea fan Gorgonia ventalina. This work includes two studies on the current status of aspergillosis in populations of G. ventalina in several reefs off La Parguera, Puerto Rico. The first study evaluated disease prevalence and virulence while the second investigated the effects of the disease on the reproduction of G. ventalina. Aspergillosis prevalence was explored through surveys performed over a two-year period at varying depths within six reefs along an inshore-offshore gradient. The average prevalence of aspergillosis increased from 3% (95%CI: 1.8-6.0%) in March 2005 to 17% (95%CI: 14.8-19.5%) in September 2006, with values for individual reefs varying from 0-29%. Prevalence was most related to reef and depth, but season, year, reef zone and density of sea fans also had some influence. The highest prevalence was found at Turrumote, Media Luna and Enrique at depths shallower than 9.6 m in 2006. Aspergillosis virulence was monitored on tagged colonies for fifteen months in three reefs to assess the spatial and temporal dynamics of individual disease lesions, the rate of advance and tissue mortality, the seasonal variability, and the rate of recovery. Trends were consistent among all sites; the number of active lesions (May 2006: 3.08 lesions/colony, W=1-23, n=61; July 2007: 0.72 lesions/colony, W=0-4, n=61) and the area of purpling due to disease (May 2006: 3.44%, W=0.05-21.32, n=61; July 2007: 0.51%, W=0-3.35, n=61) decreased over time as the aspergillosis infection disappeared, while the area of tissue loss per colony (May 2006: 1.92%, W=0-19.53, n=61; July 2007: 13.46%, W=0-100, n=61) increased over time as a consequence of the infections. The effect of aspergillosis on reproductive output was investigated using histological techniques to observe eggs and spermaries in tissue samples collected from both healthy colonies and colonies with signs of aspergillosis. In diseased colonies, there was a significant decrease in the proportion of reproductive polyps and in the number of eggs per polyp in the infected area (4.1% reproductive polyps, 95%CI: 2.6-6.5; 0.06 eggs/polyp, W=0-0.6, n=24) and immediately adjacent to it (12.4% reproductive polyps, 95%CI: 9.7-15.6; 0.18 eggs/polyp, W=0-2.0, n=24) compared to areas at least 10cm away from lesions in healthy-looking tissue (34.4% reproductive polyps, 95%CI: 30.2-38.7; 0.50 eggs/polyp, W=0.05-1.5, n=24). The impact seems to be systemic since even polyps in healthy-looking areas of infected colonies showed decreased egg and sperm production compared to healthy colonies (41.2% reproductive polyps, 95%CI: 38.0-44.2; 0.76 eggs/polyp, W=0.05-3.35, n=100). The long-term effect of this reduction in gamete production depends on whether it drops low enough to limit recruitment causing a decline in the population or produces a recruit population which is not reduced in size but is more resistant to disease. |
