Defecation Rate of Three Tubificid Oligochaetes Found in the Sediment of Toronto Harbour, Ontario

Abstract

The defecation rate of three tubificids is affected by temperature but the effect differs from species to species. Information on defecation rate and weight change at each experimental temperature suggests an optimum temperature range of 14 C for Peloscolex multisetosus, 18 C for Tubifex tubifex, and greater than 20 C for Limnodrilus hoffmeisteri. Downward trends of defecation rate with time were recorded for P. multisetosus, but these were probably due to lowered activity prior to the observed mortality. Upward trends in defecation rate with time in L. hoffmeisteri may indicate continuing acclimation to experimental conditions beyond their 10- to 14-day duration, or a need to process increasing amounts of less nutritious mud because of selective feeding on the richer fractions at the beginning of the assay period. Data on the relative abundance and distribution of species in Toronto Harbour is used to estimate defecation rates of the tubificid populations in the field.