PARENT SESSION
Oral Session #48: Spatial patterns, spatial processes. Presiding: D. Deutschman.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Madison Ballroom C.
Disease transmission of aspergillosis in sea fans: inferring process from spatial pattern.
Jolles, Anna1,2, Sullivan, Patrick1, Alker, Alisa1, Harvell, C. Drew1, 1 2
ABSTRACT- Despite an increase in impacts due to disease in the ocean, quantitative studies of disease processes in natural populations still lag far behind terrestrial systems. In particular, transmission processes and the detectability of local transmission of disease are poorly known in relatively open marine systems. We studied infection of sea fans Gorgonia ventalina by the fungus Aspergillus sydowii. To assess detectability and mechanisms of secondary transmission of the fungus, we analyzed the spatial distribution of disease among the fans, using Ripley's K as a measure of disease aggregation. Gorgonian corals are an unusually tractable system for studying spatial patterns of disease, because they occur at high local densities, show high prevalence of some diseases and are sessile. Coral populations and disease were mapped at three different reefs in the Florida Keys varying in disease prevalence and severity. Where disease prevalence was relatively low, the disease was distributed randomly among the aggregated sea fans. This is consistent with disease transmission by input of infectious fungal material from terrestrial sources only. However, where disease prevalence was high, the disease was significantly aggregated among sea fans at the 2-8 meter scale. The aggregated distribution of disease among sea fans is consistent with secondary transmission from fan to fan when disease levels are high. Such transmission could take place by direct physical contact between neighboring fans as they brush against each other. Further, infected fans might shed fungal material into the water column, and other fans become infected by these fomites. Our results suggest that water-borne transmission occurs, but transmission by physical contact is also a likely component. We further show that the observed aggregation pattern of disease is not a result of clustering of larger fans, despite higher disease prevalence in larger fans. Although our results are consistent with secondary transmission of fungal fomites from infected fans, we cannot exclude alternate hypotheses, such as fans in a small local area sharing a common environment with higher fomite densities or compromised host resistance.
KEY WORDS: disease ecology, coral reef, spatial statistics