Environmental and Fish Community Influences on Presence of a Microsporidian Parasite in Mottled Sculpin

Disease can play a critical role in structuring fish population, although little is known about the factors that influence the spatial distribution of disease in aquatic ecosystems. Knowledge of these complex ecological processes could enhance population risk-assessment capabilities and improve forecasting the spread of infectious disease. Mottled sculpin and the microsporidian parasite Glugea spp. provide an ideal host-parasite system for investigating patterns of disease spatial distribution due to the host species’ broad range and high abundance, as well as the parasite’s dichotomous nature of either high prevalence or near complete absence. We evaluated fish community composition and 15 environmental variables in 5 streams with infected mottled sculpin populations and 7 streams without infection. Presence of the parasite was not significantly related to any of the measured environmental variables, although water temperature appeared positively correlated with likelihood of infection. Within-basin land use showed no relationship with disease prevalence. A marginally significant difference exists among the fish communities in infected and uninfected streams, further supporting the importance of water temperature in determining disease presence. Additionally, mottled sculpin were observed to have lower densities and relative abundances in infected streams, suggesting a potential host population abundance regulation role for the parasite.