The effects of water temperature, ionic content and total dissolved solids on Nephelopsis obscura and Erpobdella punctata (Hirudinoidea, Erpobdellidae)

Using a three-way factorial experimental design the effects of water temperature, ionic content (water type) and total dissolved solids on the mortality rates of Nephelopsis obscura and Erpobdella punctata were examined. A strong interaction between temperature and water type and temperature and total dissolved solids was observed on the mortality of E. punctata . Other than differences in mortality due to reproductive condition, N. obscura showed uniformly low mortality not significantly affected by temperature, water type or total dissolved solids. Thus the numerical dominance shown by N. obscura in Alberta and Western Canada could be explained by the differentially higher mortality of E. punctata with respect to the three tested independent variables.