1. The impact of ultraviolet-B (UVB)-irradiated phytoplankton on the life history parameters of Daphnia was studied. Three species of Chlorophyceae (Chlamydomonas reinhardtii, Scenedesmus acutus and S. subspicatus) and one species of Cryptophyceae (Cryptomonas pyrenoidifera) were cultured with and without exposure to UVB radiation (biologically effective dose of 3 kJ m–2 day–1 DNA weighted) and fed to Daphnia pulex.
2. The daphnids feeding on UVB-irradiated algae tended to be smaller in size, to produce less and smaller offspring, and to have a reduced population growth rate.
3. Fatty acid (FA) analysis of the phytoplankton showed a reduced total FA content under UVB radiation for all four species. Changes in the content of unsaturated fatty acids (UFA) were species specific.
4. The results indicate that the energy transfer between the primary producers’ and grazers’ level might be negatively influenced by UVB radiation. Direct effects on food quality are modest but detectable, changes in quantity or species composition may be more important in the energy transfer.