The combined effects of heavy metals (copper and zinc), temperature and food (Chlorella vulgaris) level on the demographic characters of Moina macrocopa (Crustacea: Cladocera)

Abstract

In this work we evaluated the effect of temperature (22 degrees and 27 degrees C), algal density (Chlorella vulgaris 0.5 x 10(6) and 2.0 x 10(6) cells/mL) and different combinations of 2 heavy metals (Zn at 25.25-101.0 microg/L and Cu at 17.75-71.0 microg/L) on the population level variables of Moina macrocopa. Median lethal concentration (24 h bioassay at 1 x 10(6) cells/mL of algal diet) of Zn and Cu for M. macrocopa were 1010 microg/L and 710 microg/L, respectively. In the survivorship curves at 27 degrees C there was a reduction in the survival of cladocerans exposed to Cu compared to controls or Zn. The fecundity curves (m(x)) indicated a steady reproductive output throughout the life span of M. macrocopa, but the negative impact of copper was more than that of zinc. Reproductive phase of M. macrocopa was longer at 22 degrees C than at 27 degrees C. The average lifespan was higher at 22 degrees C and at the higher food level. It was significantly affected by temperature, food level and toxicant concentration, as well as their interaction. The net reproductive rate was also influenced by food and temperature but not by the toxicant level. The generation time ranged between 4-8 days and was lower at 27 degrees C. The population growth rate (r) derived from life table experiments varied from 0.6 to 0.9 per day, depending on the treatment. Regardless of the toxicant level, at 22 degrees C, the population growth was higher at the higher food level. In treatments containing only Cu, the population growth of M. macrocopa was lower than when present together with Zn. Peak population densities of around 30 ind./mL were reached under high food conditions. Higher temperature and lower food level had an adverse effect on M. macrocopa in treatments containing only Cu. In the presence of higher food density, the adverse impact of copper was not evident. The r derived from growth study ranged from 0.25 to 0.64 per day depending on the test conditions. Data were interpreted in terms of sensitivity M. macrocopa for its possible use as a complement, but not as an alternative to Daphnia magna for evaluating the toxicity of heavy metals.