The influence of algal densities on the toxicity of chromium for Ceriodaphnia dubia Richard (Cladocera, Crustacea)

Abstract

Food availability may affect metal toxicity for aquatic organisms. In the present study, the influence of high, medium and low densities of the algae Pseudokirchneriella subcapitata (10 6 , 10 5 and 10 4 cells.mL -1, respectively) on the chronic toxicity of chromium to the cladoceran Ceriodaphnia dubia was investigated. C. dubia was exposed to a range of chromium concentration from 2.71 to 34.04 mg.L -1 and fed with algae at various densities. In another experiment, the green alga was exposed to chromium concentrations (94 to 774 mg.L ) and supplied as food in different densities to zooplankton. The survival and reproduction of the cladoceran were measured in these toxicity tests. The IC50 for Cr to P. subcapitata and metal accumulated by algal cells were determined. The results of a bifactorial analysis (metal versus algal densities) showed that metal toxicity to zooplankton was dependent on algal densities. Significant toxic effects on the reproduction and survival of C. dubia were observed at 8.73, 18.22 and 34.04 mg.L -1 Cr when the test organisms were fed with 10 6 cells.mL -1 of P. subcapitata. Although the chlorophyta retain low chromium content, a decrease in the reproduction and survival of C. dubia occurred when they were fed with high algal density contaminated with 774 mg.L -1 Cr. It was concluded that high algal density have an appreciable influence on chromium toxicity to daphnids.Keywords: metal, chronic toxicity, food, Pseudokirchneriella subcapitata, zooplankton.Influência de diferentes densidades algais sobre a toxicidade do cromo para Ceriodaphnia dubia Richard (Crustacea, Cladocera) Resumo A disponibilidade de alimento pode afetar a toxicidade dos metais para os organismos aquáticos. No presente estudo, a influência de alta, média e baixa densidades da alga Pseudokirchneriella subcapitata (10 6 , 10 5 e 10 4 céls.mL -1 , respectivamente) sobre a toxicidade crônica do cromo para o cladócero Ceriodaphnia dubia foi investigada. C. dubia foi exposta a uma faixa de concentração de cromo de 2,71 a 34,04 mg.L -1 e alimentada com diferentes densidades algais. Em outro experimento, a alga foi exposta a concentrações de cromo (94 a 774 mg.L -1 ) e oferecida como alimento ao cladócero em diferentes densidades. A sobrevivência e a reprodução do cladócero foram medidas nesses testes de toxicidade. O valor da CI50 do cromo para P. subcapitata e a concentração de metal retido pelas células algais foram determinados. Os resultados da análise bifatorial (metal versus densidades algais) mostraram que a toxicidade do metal ao zooplâncton foi dependente da densidade algal. Efeitos tóxicos significativos na sobrevivência e reprodução de C. dubia foram observados a 8,73, 18,22 e 34,04 mg.L -1 Cr quando o organismo-teste foi alimentado com 10 6 céls.mL -1 de P. subcapitata. Apesar de a alga reter pouco cromo, decréscimo na sobrevivência e na reprodução de C. dubia ocorreu quando alimentada com alta densidade algal contaminada com 774 mg.L -1 Cr. Concluiu-se que alta densidade algal tem uma considerável...

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