Aspergillosis in sea fans: Fungal community, patterns of prevalence, and genetic variability of Aspergillus flavus

Populations of sea fans Gorgonia ventalina have been impacted by aspergillosis outbreaks through the Caribbean. Eventhough aspergillosis is one of the most characterized marine disease, issues regarding the identity of resident mycoflora in healthy and diseased sea fans, its spatial variation, source of pathogenic fungi and host-fungi specificity are not well understood. Focusing in these issues will increase our understanding of the role of natural mycoflora in the disease, and the effect of aspergillosis in survivorship of sea fans. The main objectives of this dissertation were to determine: (1) the spatial variation in the mycoflora of healthy and diseased sea fans and surrounding seawater; (2) the main cause of mortality of sea fans; (3) the spatial variation in incidence and prevalence of aspergillosis; (4) the pathogen-host specificity using Aspergillus flavus as a model system; and (5) identify possible source of marine and pathogenic strains.;Significant spatial variation of mycoflora in sea fans (healthy and diseased) was found, in addition to high similarity in the mycoflora of nearshore and offshore seawater. Seawater mycoflora was similar to sea fan mycoflora. Aspergillus sydowii considered the sole pathogen of sea fan aspergillosis was isolated from healthy colonies but not from diseased ones. Environmental factors such as water quality and temperature seems to be influencing spatial variation in sea fan and sea water mycoflora. However, no spatial and temporal variations were found in incidence and prevalence of aspergillosis. Detachment was the main cause of mortality, and aspergillosis seems to have a low regulatory role in population dynamics of sea fans. Phylogenetic approach, using A. flavus as model system showed a high polymorphic species with high dispersion capacity, and no genetic structure (Fst=0.002), suggesting a one big panmictic population. The data suggests that any A. flavus strain can colonize sea fans, and the expression of aspergillosis appears to be more linked to environmental factors. Virulence of sea fan aspergillosis appears to be more related to environmental changes stressing the host, than to genetic-based differences in virulence among fungal strains. Future studies should focus at the synergism (environment - host - mycoflora) to understand the effect of disease in sea fan populations especially in light of the complexity that this disease exhibits.