Increased microsporidian parasitism of the crayfish Orconectes virilis in an experimentally acidified lake. France, R., L. & Graham, R., L. Water, Air, and Soil Pollution, 26:129-136, 1985.
Increased microsporidian parasitism of the crayfish Orconectes virilis in an experimentally acidified lake [pdf]Paper  abstract   bibtex   
Orconectes vMlis has been identified as a host of the microsporidian Thelohania contejeani in four lakes in the Experimental Lakes Area (ELA), northwestern Ontario. Prevalence of parasitism increased from 1.7% in autumn 1979, to 6.5% and 7.7% in autumns 1980 and 1981 concomitant with experimental acidification of Lake 223 to pH 5.1. By comparison, mean infection rates observed within three reference lakes were between 0.3 to 0.6%. Enhanced microsporidosis is believed to have contributed to a reduction in annual crayfish survival rates for the Lake 223 population of 8% in 1979 and 18% in 1980 compared to averages calculated for the non-acidified lakes. Hypotheses to explain the ten-fold increase in Thelohania parasitism in Lake 223 over background levels for the ELA region include a) increased probagative ability due to elevated rate of crayfish cannibalism or low pH-favored parasite life cycle, and b) decreased host resistance when under sublethal stress.

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