THE ABUNDANCE OF EPIZOIC CILIATE EPISTYLIS-DAPHNIAE RELATED TO THEIR HOST MOINA-MACROCOPA IN AN URBAN STREAM

The numerical abundance of epizoic ciliate Epistylis daphniae attached to cladoceran host Moina macrocopa in an urban stream Weijin River was studied from April to October, 1990. The population size both of M. macrocopa and of E. daphniae fluctuated greatly. The infection proportion of M. macrocopa ranged from 36.67 to 100% depending on the sampling date and the average infection proportion was 92.4%. The mean biomass of E. daphniae attached to M. macrocopa was 0.048 mg dry wt/liter and was about 3.26% of the mean host biomass. The mean number of E. daphniae zooids per host was 31.46 (ranged from 3.17 to 85.38) and it was significantly higher in large group of hosts (< 0.8 mm) than small group (> 0.8 mm). In midsummer, the mean number of the epizoites per host reached its peak (more than 80 zooids per host) and was associated with lower abundance of M. macrocopa . Other relationships between number of E. daphniae zooids per M. macrocopa and various aspects of the M. macrocopa life cycle were also studied.