Comparison between a Normal and a Cr-Tolerant Strain ofScenedesmus acutusas a Food Source toDaphnia magna

A normal (S2-N) and a Cr-tolerant (S2-T) strain ofScenedesmus acutus,grown in Cr-free medium or in the presence of 1, 5, or 10 mg/liter Cr(VI), were fed toDaphnia magna.An increase of growth and fecundity was observed in the daphnids when the algae had undergone an increase of dry mass following Cr treatment, which happened in S2-N in the presence of 1 mg/liter and in S2-T in the presence of 5 mg/liter. When the algae were pretreated with 10 mg/liter, growth and fecundity were reduced in the daphnids fed on S2-N, but remained normal in the daphnids fed on S2-T. It is concluded that the tolerant strain remains a good food source even if grown in the presence of a Cr concentration that reduces the nutritional value of the normal strain.