The life history and production of the leech Helobdella stagnalis (Hirudinea:Glossiphonidae) in the River Ely, South Wales

A population of the glossiphonid leech Helobdella stagnalis was studied over a period of 16 months in the organically polluted River Ely, South Wales. There were two generations each year. The overwintering population released young (the spring‐brood) in June. The spring‐brood in turn produced their own offspring (summer‐brood) in August. Seasonal patterns of mortality were related to flow, temperature and life‐cycle stage. Individual growth rates were dependent upon both temperature and life‐cycle stage. Annual population production (P) was 7.56 g wet wt m‐2, mean annual population biomass (B) was 1.43 g wet wt m‐2 and the annual P/B ratio was 5.29.