Variations in the toxicity of Microcystis species to Moina macrocopa

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Abstract
SUMMARY: The toxins of 23 strains of Microcystis spp. were analyzed and the toxicity of these strains to Moina macrocopa was tested. There were great variations among strains in the amounts of microcystins. Most strains contained toxins and only five out of 23 strains contained no toxins. However, eight strains did not kill any M. macrocopa individuals over 7 days. Conversely, strains containing a large amount of microcystin exhibited very strong toxicity against M. macrocopa, killing 50% after 6 h of exposure. However, the microcystins themselves do not seem to be a major lethal factor against cladocerans. Some strains were not lethal to M. macrocopa, although they contained a quite high concentration of microcystins suggesting the presence of a co‐agent acting together with microcystin. Non‐toxic strains of Microcystis showed variations in their effects on M. macrocopa growth. Microcystis elabens, which does not contain microcystins, was slightly toxic to M. macrocopa. Moina macrocopa starved to death when offered Microcystis holsatica, suggesting that the cla‐doceran might avoid this blue‐green alga.