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Daphnia pulex (Crustacea, Cladocera) was fed the blue‐green algae (Cyanophyceae) Anacystis nidulans, Synechococcus elongata, S. cedrorum, Merismopedia sp., Anabaena flosaquae, Synechocystis sp., and Gloeocapsa alpicola. The green algae (Chlorophyceae) Ankistrodesmus falcatus and Chlorella vulgaris were used for comparison. Direct observations were made of D. pulex feeding in depression slides filled with the test food. Food labeled with 14 C was used to determine ingestion and assimilation. Life tables were constructed for cohorts fed blue‐greens, greens, and no food, and survivorship ( l x ), net reproductive rate ( R o ), median age of death, and intrinsic rate of natural increase ( r ) were calculated. In all cases, ingestion, assimilation, survivorship, and reproduction of D. pulex fed blue‐green algae were lower than of those fed green algae, although there were differences among the blue‐greens in their effects on these parameters. Anacystis nidulans, Merismopedia sp., and Synechocystis sp. showed some toxicity or inhibition towards D. pulex. Although some blue‐green algae can be ingested and assimilated by D. pulex, few if any of those tested provide sufficient nutrition to support a population that does not have other food available.
Dean E. Arnold (Mon,) studied this question.