First Report on Chronic Effects of Non-Microcystin Producing Cyanobacteria, Cylindrospermopsis Curvispora and Planktothrix sp., on Daphnia Magna

Abstract

Cyanobacteria are an essential part of aquatic ecosystems. However, they can cause detrimental impacts on other organisms of higher tropic levels in water bodies because of their potent toxic metabolites (e.g. microcystin) and other bioactive compounds. In this study we tested the long-term and negative effects of two non-microcystin producing cyanobacteria Cylindrospermopsis curvispora and Planktothrix sp. from Vietnam on Daphnia magna under the laboratory conditions. The animal was fed with mixtures of green alga, Scenedesmus sp., and C. curvispora or Planktothrix sp. at different ratios (100 % Scenedesmus, 10 % cyanobacteria + 90 % Scenedesmus, 50 % cyanobacteria + 50 % Scenedesmus, 100 % cyanobacteria) over a period of 21days. The results showed that the D. magna fed with from 10 to 100 % cyanobacteria reduced their survival with density dependence, delayed or postponed its maturation. Besides, the cyanobacteria also inhibited the reproduction of adult D. magna consequently strongly prevent the next population development of D. magna. The species C. curvispora had stronger effect on survival, but less impact on maturation and reproduction of D. magna than Planktothrix sp, negatively. To our knowledge, this is the first report on negative effects of C. curvispora and Planktothrix sp. from Vietnam on life history traits of D. magna. Additionally, our results revealed that even non-microcystin producing cyanobacteria at low density could also have negative impacts on zooplankton consequently ecological balance interference. In situ investigations on the effects of cyanobacteria on zooplankton are suggested for more understanding on the ecological interactions of the two trophic levels of aquatic ecosystem.