Pathogens compromise reproduction and induce melanization in Caribbean sea fans

The fungal pathogen Aspergillus sydowii is causing high mortality of sea fan gorgonians Gorgonia ventalina in a Caribbean-wide outbreak. Fungal infection induces a localized band of melanin adjacent to fungal hyphae. We also detected an unidentified parasite that induced a similar melanin band, suggesting that melanization is a generalized response to infection. Although a common mechanism of antifungal defense in insects, this is the first report of melanization in a cnidarian. Histological analysis also revealed that sea fans are gonochoric, and reproduction was suppressed in fungus-infected colonies throughout the year. Fans infected with the fungus contained few or no gametes in comparison to fecund healthy fans. Every fan with fungal lesions covering between 10 and 20% of fan area was reproductively compromised; 64% of infected fans were reproductively inactive. Since prevalence of infection increases with increasing colony size, compromised reproductive of the largest, most fecund fans will amplify the epizootiological and selective impacts of this outbreak. This new evidence suggesting reproductive suppression in diseased gorgonians indicates that demographic costs may occur for those populations surviving disease outbreaks.