Combined effects of exposure time and copper toxicity on the demography of Moina macrocopa (Crustacea: Cladocera)

Cohort life table experiments were conducted on M. macrocopa using copper at three nominal concentrations (as CuSO₄, 0.1, 0.2 and 0.4 mg L^{? 1}, in addition to controls) for different periods of exposure (3 to 24 h). Age-specific survivorship of M. macrocopa decreased in relation to age of the cohort, concentration and duration of exposure to copper. Age-specific life expectancy curves also decreased with increasing age of the cohort. However, at low copper levels and shorter exposure time, there was an increase in life expectancy when the cohort was about 10 day old. Fecundity (m _x ) was nearly regular in controls; however, at higher copper levels and longer duration of exposure, the offspring production was more oscillating. The offspring production completely ceased when continuously exposed to CuSO₄ at 0.4 mg L^{? 1}. Most of the measured demography variables significantly decreased with increasing concentration of Cu in the medium. The average lifespan and life expectancy at birth varied 2.9 to 9.6 and 2.4 to 9.1 days, respectively. Gross reproductive rate (GRR) varied from 31 to 89 offspring female^{? 1} lifespan^{? 1}, while the survival-weighted net reproductive rates were nearly one-third of the GRR. Generation time of M. macrocopa varied from 5 to 7 days while the rate of population increase ranged from 0.36 to 0.84 per day. The results are discussed in relation to the sensitivity of M. macrocopa to copper toxicity and the necessity of amending the national water quality criteria in Mexico.