Stages of infection and ecological effects of a fungal epidemic on the eggs of a limnetic copepod

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Abstract
SUMMARY. Fungal infection of calanoid copepod (Diaptomus novamexicanus) eggs was observed in each of three years in an alpine lake (Castle Lake, California, U.S.A.). Stages in the infection process were examined by light and scanning electron microscopy and evidence was obtained that the Lagenidium‐like fungus concerned was a virulent parasite. Fungal destruction of eggs varied in timing and severity from year to year. The maximum impact of the disease was an estimated 48.4% decrease in potential copepod recruitment in 1976 due to the onset of a severe epidemic early in the summer growing season. The minimum impact, a 5.6% decrease in potential recruitment, was recorded in 1975. In this year the proportion of infected eggs was reduced and large numbers of juveniles had been released before the fungal disease began. The 1974 epidemic was intermediate in severity. The effect of these epidemics on Castle Lake calanoid populations is discussed in relation to temperature, food availability and predation.