Effects of thermal effluent on the population dynamics of Physa gyrina say (mollusca: gastropoda) and its helminth parasites at Wabamun Lake,Alberta / Chandra S. Sankurathri

Effects of thermal effluent on the population dynamics of Physa gyrina (Mollusca: Pulmonata), its larval helminth parasites, and populations of Chaetogaster l. limnaei and C. 1. vaghini were studied at Wabamun Lake,Alberta, from May 1971 to August 1973. Thermal effluents increased the rate of development and growth of P. gyrina, and allowed continous reproductive activity throughout the year. These changes, and the increased period of growth of aquatic macrophytes, resulted in increased population densities of P. gyrina in the heated area. Temperatures below 10 degrees or small amounts of vegetation can apparently control the population of P. gyrina in the winter. Thermal effluents provided the necessary conditions to maintain trematode transmission throughout the year, increased the prevalence of certain parasites, especially metacercarial stages, and enhanced parasite populations in definitive hosts during the winter. Thermal effluents eliminated or reduced C. 1 limnaei (which are