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Abstract
Issue Title: Cladocera: Proc. of the VIth Int. Symp. on Cladocera, held in Wierzba, Poland, 19-23 August 2002
In most toxicity studies using Cladocera, bioassays are routinely done to determine median lethal concentration (LC^sub 50^) or the responses to sublethal exposure. However, information on the patterns of recovery of cladocerans exposed to different concentrations of toxicants is scarce. This is important because cladocerans exposed to toxicants for a short duration may later recuperate under favourable conditions. Using the life table demographic and population growth, the present study was conducted to evaluate the recovery patterns of Monia macrocopa exposed to five different concentrations (0, 25, 50, 75 and 100% of 24 h LC^sub 50^ for CdCl^sub 2^ or methyl parathion) and then returned to toxicant-free medium containing alga (Chlorella vulgaris) at low (0.25 × 10^sup 6^cells ml^sup -1^), medium (0.5 × 10^sup 6^cells ml^sup -1^) or high (1 × 10^sup 6^cells ml^sup -1^) levels. We measured selected life history variables such as average lifespan, life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase. Results indicated that regardless of food concentration, surviving individuals of M. macrocopa exposed to a median lethal concentration did not recover. The effect of food level was significant at 25 and 50% of the median lethal concentration for cadmium or methyl parathion. Age-specific fecundity curves showed that exposure to either toxicant for a duration as short as 24 h at one-fourth of the LC^sub 50^ showed reduced output of offspring, especially at a lower food level. At and above exposures of 0.037 mgl^sup -1^ of methyl parathion, no reproduction occurred. The highest gross and net reproductive rates (127 and 55 offspring female^sup -1^) were obtained in controls at the high (1 × 10^sup 6^ cells ml^sup -1^) algal food level. The rate of population increase obtained from life table data was around 0.7 per day in controls but decreased when exposed to toxicant concentrations. The rates of population increase per day derived from population growth data varied from 0.22 to 0.33 per day for the controls, depending on the food levels.[PUBLICATION ABSTRACT]