Two-day life cycle tests with the rotifer Brachionus calyciflorus were run to study the nutritional quality effects to rotifers ofScenedesmus pectinatus grown under non-limiting, nitrogen limiting and phosphorus limiting conditions and the feedback of therotifers on the food algae. Under nutrient-limited conditions of its algal food Brachionus production was depressed, animals producedfewer eggs and were smaller sized. Clearance rates of Brachionus offered non-nutrient-limited and nutrient-limited foodwere similar. The number of cells per colony was similar for S. pectinatus under nitrogen limited and phosphorus limited conditionsboth in the absence and presence of Brachionus. Cell volumes of phosphorus limited S. pectinatus were larger than thoseof nitrogen limited cells. The most dramatic response of the food alga S. pectinatus was observed in non-nutrient-limited conditions:a strong size enlargement occurred only in the presence of Brachionus. This was caused by a higher share of eight-celledcolonies and larger individual cell volumes in the presence of rotifers than in their absence. S. pectinatus might gain an advantageof becoming larger in moving out of the feeding window of its enemy, but nutrient limited conditions might undermine theeffectiveness of such reaction.