Life history consequences for Daphnia pulex feeding on nutrient-limited phytoplankton

1. The growth and feeding of Daphnia pulex De Geer on different algal species was examined. The green algae Chlamydomonas reinhardtii Dangeard and Scenedesmus acutus Meyen, the diatom Synedra tenuissima Kutzing, the cryptophyte Cryptomonas pyrenoidifera Geitler and the cyanobacterium Microcystis aeruginosa Kutzing were cultured in nonlimiting and in N- or P-limiting medium and used as food for D. pulex. 2. Growth limitations were reflected in the elemental and biochemical composition and the morphological characteristics of the algal resources. 3. The clearance rates of D. pulex feeding on nutrient-limited algae were reduced. This was not observed when nutrient-limited mutant Chlamydomonas cells without cell walls were used as food, indicating that the cell wall may play an important part. 4. In comparison with animals grown on nutrient-sufficient cells, nutrient-limited algae resulted in smaller body length, reduced brood sizes, reduced size at maturity, increased age at first reproduction and, consequently, in reduced Daphnia population growth rates. 5. Daphnia population growth rates (r) were negatively correlated with the C:P ratio and the carbohydrate content of the food. Moreover, significant correlations between r and clearance rates were found. 6. The observed differences in the grazing and the life history parameters of Daphnia feeding on non-limited and nutrient-limited algae may be the result of both reduced nutritional value and reduced digestibility of nutrient-limited algae.