| Summary: | Valle de Bravo reservoir supplies drinking water to 40% of Mexico City. Here we present data on the population growth and life-table demography of the cladoceran <i>Daphnia pulex</i>, cultured at temperatures of 20 °C and 25 °C and with different concentrations of the crude extracts from blooms of <i>Microcystis aeruginosa</i>, collected in January, and <i>Woronichinia naegeliana</i>, collected in September. We hypothesized that <i>Daphnia pulex</i> would be more sensitive at the higher temperature and to toxins from <i>W. naegeliana</i> as these blooms have been shown to be more toxic to rotifers. We extracted the toxins and conducted acute toxicity tests at eight concentrations of microcystins at 20 °C. The LC50 was 26.8 µg/L and 11.5 µg/L, respectively, for <i>Microcystis</i> and <i>Woronichinia</i> samples. The chronic toxicity tests included population growth and life-table demography studies at 5 and 10% of the LC50 concentration, at 20 °C and 25 °C. Four replicates for each of the three treatments, which consisted of treatments with low and high cyanotoxin levels and a control without cyanotoxins, were set up. The population growth rate ranged from 0.18 to 0.42 d<sup>−1</sup> on the extracts from <i>M. aeruginosa</i> (January) and from 0.2 to 0.31 on extracts from <i>W. naegeliana</i>. <i>Daphnia</i>, being better adapted to cooler temperatures, was more adversely affected at 25 °C than 20 °C. The adverse effect of cyanobacterial extracts was greater from <i>Microcystis</i> than <i>Woronichinia</i> blooms. The tolerance of <i>Daphnia pulex</i> to cyanotoxins depends on the bloom-forming species and the temperature.
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