Disease Resistance in Sea Fan Corals and the Host Range of the Fungal Pathogen

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Harvell The incidence of disease among tropical marine organisms appears to be increasing and indeed is thought by some that it will increase due to global warming and anthropogenic causes. Yet we lack critical knowledge to manage disease in tropical marine systems. Not only do most tropical marine pathogens, including the widely studied coral band disease, remain unidentified, but the mechanism of resistance to even identified pathogens is unstudied. The paucity of information is particularly problematic for there is little scientific basis for devising protocols for management of diseased populations in the oceans. An ongoing fungal epizootic among Caribbean gorgonian corals provides an unprecedented opportunity to study the dynamics of an emergent disease and the mechanisms of host resistance. The sea fan-Aspergillus sydowii interaction is unusually tractable because: 1) Lesions can be followed on the 2-dimensional fan surface by videography 2) the fungus can be readily isolated from nature, cultured in the laboratory, and used in bioassay for resistance studies, and 3) corals can be infected in the laboratory with pure inocula and in the field by grafting diseased onto healthy ones. The objectives of this study are to: 1) determine the host range of the fungal pathogen A. sydowii among Caribbean gorgonians, 2) experimentally evaluate the mechanisms of sea fan resistance, and 3) evaluate the role of temperature in disease resistance and pathogen virulence. If Aspergillus is not restricted to Gorgonia, then this epizootic could have far greater impact on Caribbean reefs, many of which are dominated by sea fans and other gorgonian corals. Understanding the mechanisms of natural resistance is important in evaluating whether the spate of new diseases is caused by new disease introductions, lowered resistance of corals due to anthropogenic stresses, or a combination of both. Because the identity of the pathogen is known and in culture, and because we are able to infect sea fan under experimental conditions, we will be able to study the interactions among host defenses, pathogen dynamics, and environmental conditions.