RELATIVE NUTRITIONAL-VALUE OF CILIATE PROTOZOA AND ALGAE AS FOOD FOR DAPHNIA

The relative importance of autotrophic flagellates, desmids, cyanobacteria, and ciliates as food for Daphnia magna was examined using cohort life tables. Each cohort was fed a single food type at a given concentration, and comparisons among each type were made. Algal feeding treatments included three levels of young (7 to 14 days old)Chlamydomonas reinhardi (Chlorophyta, Chlamydomonadacae), two levels of senescent (> 14 days old)C. reinhardi, two levels of Cryptomonas sp. (Chlorophyta, Cryptomonadacae), two levels of Staurastrum sp. (Chlorophyta, Desmidacae), four levels of young (7 to 15 days old) or senescent (> 15 days old)Microcystis aeruginosa (Cyanophyta, Chlorococcacae), and a no-food treatment. The ciliates Cyclidium sp. and Paramecium caudatum were also presented at concentrations of 1 or 102 cells/ml, as well as mixtures of C. reinhardi (103/ml) and Cyclidium (1/ml) or P. caudatum (1/ml). Daphnia growth, reproduction, and survivorship were highest when C. reinhardi or Cryptomonas were the food source, while those starved or fed M. aeruginosa had shorter survivorship and lower growth and reproduction. Daphnia grew and had high survivorship when fed P. caudatum, but even though eggs were produced, most were aborted after 2 or 3 days. Staurastrum and Cyclidium produced intermediate growth and survivorship, but reproduction was seen only in the 103Staurastrum/ml treatment. Carbon and nitrogen content were general indicators of nutritional value. However, growth, reproduction, and survivorship were higher in some cohorts fed treatments containing relatively low levels of carbon and nitrogen. Other cohorts were short-lived and did not reproduce, despite being fed much higher levels of carbon and nitrogen. The results also suggest that green algae are nutritionally valuable for Daphnia, whereas cyanobacteria are not. As measured by life-table parameters, the nutritional value of ciliates was variable, with some being poor food sources. Thus, the potential of ciliates as a trophic link between microbial production and higher trophic levels may vary with the ciliate community structure. Our results suggest that ciliates alone were insufficient as a food source to support Daphnia population growth. © 1990 Springer-Verlag New York Inc.