The life history and production of Asellus aquaticus (Crustacea: Isopoda) in the River Ely, South Wales

SUMMARY. A population of the isopod Asellus aquaticus was studied for sixteen months in the organically polluted River Ely. South Wales. There were two complete generations each year. The overwintering population released young (the spring-brood) over the period April-June. These animals in turn produced their own offspring (summer-brood) in late July-October. Each generation died after breeding and the overwintering population was comprised entirely of animals from the summer-brood.
Seasonal patterns of mortality were related to water flow, temperature and life-cycle stage. Individual growth rates were affected by both temperature and life-cycle stage.
Annual population production (P) was 195.68 g wet wt m^-2, mean annual biomass (B) was 32.98 g wet wt m^-2 and the annual P/B ratio was 5.93.