Population Biology of the Freshwater Snail Bulinus globosus in the Zimbabwe Highveld

Abstract

(1) The population dynamics of Bulinus globosus (Morelet), an intermediate host for urinary schistosomiasis, were studied at five river sites in the Zimbabwe highveld for between 4 and 28 months. (2) Adult snail abundance, recruitment and loss rates were monitored at weekly intervals using a mark-recapture method. Growth rates were measured on caged snails. (3) Variations in abundance of the snails were related to water temperature and water flow. Peak densities at the sites ranged from 0 01 to 0-6 snails (of shell length > 5 5 mm) litre-1. Survival rate was negatively correlated with temperature. Losses due to rainy season floods ranged up to 99 9%. (4) The relationship between recruitment rate and temperature was described by a bell curve, with peak recruitment at 20 6 'C. Recruitment rate varied between sites. This may have been due to differences in food quality (vegetation), water chemistry and/or densitydependent effects. (5) Growth rates were positively correlated with temperature. (6) Bulinus globosus populations had a temperature-dependent seasonal cycle, with rapid increases in abundance during periods of favourable temperatures. Floods or drought caused variable and irregular reductions in abundance. The implications of these opportunistic' population dynamics for snail control are discussed.