Relative tolerance of some tropical freshwater microcrustaceans to acidification

Authors: PRIYANKA MALLICK HALDER, PATHIK KUMAR JANA, SUSANTA KUMAR CHAKRABORTY, SAMIR BANERJEE

Abstract: The present work reports on the effects of low pH values on the mortality of 3 freshwater zooplankton available in the freshwater ponds of Midnapore district. Acute bioassay tests on Daphnia lumholtzi, Moina brachiata, and Heliodiaptomus viduus to varying acidic pH levels of water were performed in the laboratory using serial grades of hydrochloric acid solution. Among the 3 genera, M. brachiata was found to respond sharply to acid stress in a 1-h assay, since 100% mortality was achieved at pH 5.79 (2.347 mM HCl), as compared to H. viduus, which showed 100% death in 1 h only below pH 4.9 (2.978 mM HCl). In fact, it appears that H. viduus is more tolerant to short-term acidification than M. brachiata after a 1-h exposure. This study determined that adult M. brachiata had the lowest Lc_{50} values and H. viduus had the highest Lc_{50} values at both 1 h and 24 h. The survival pattern of D. lumholtzi closely resembled that of H. viduus rather than M. brachiata. Higher sensitivity of M. brachiata, even to the slightest alteration of pH as revealed by chi-square tests (significant differences with others), has prompted us to consider this species as a sensitive indicator of aquatic pollution, particularly acidification.

Keywords: Freshwater, acidification, zooplankton, pH, bioassay

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