Spatial variation in fungal communities isolated from healthy and diseased sea fans Gorgonia ventalina and seawater

Abstract

Sea fans Gorgonia ventalina in the Caribbean are being infected by disease attributed to the fungus Aspergillus sydowii. Little is known about the natural fungal community in sea fans, including spatial variation in community composition and the source of inoculum. Patterns of spatial variation may provide important clues to the source of pathogens and etiology of the disease. The objectives of this study were: (1) to measure spatial variation in the mycoflora associated with diseased and healthy colonies of G. ventalina; and (2) to compare the mycoflora of sea fans with the mycoflora isolated from surrounding seawater. Samples of diseased and healthy sea fan tissue and seawater were collected from coral reefs in Puerto Rico. Fungi were isolated and identified by morphology and sequencing of the nuclear ribosomal internal transcribed spacer region. Twenty-six species of fungi were identified. A. flavus was the most common species isolated from both seawater and sea fan tissue. Higher species richness was found in seawater than in sea fans. Mycoflora of healthy and diseased sea fans differed among sites. Fungal species richness in seawater was higher nearshore than offshore. However, community composition in seawater did not vary spatially. The fungal community of sea fans was not different from that of the surrounding seawater, suggesting low specificity. Our data suggest that the source of offshore mycoflora is the nearshore fungal community, with richness diluted as a result of ocean circulation. Prevalence of aspergillosis was not correlated with fungal species richness but was positively correlated with the number of fungal strains isolated. The fact that diseased fans did not have lower species richness suggests that the disease is not due to a single pathogen, but rather to a variety of opportunistic pathogens.