Algal nutrient limitation affects rotifer growth rate but not ingestion rate

Abstract

The food algae Scenedesmus acutus and Cyclotella meneghiniana were grown in chemostats in a modified WC medium at identical growth rates (0.4 d‒1) but under different nutrient regimes. Nitrate or phosphate was reduced to produce N‐ or P‐limited algae. Brachionus rubens did not differentiate between nonnutrient‐limited and nutrient‐limited Scenedesmus and ingested both at comparable rates. The rotifers reached highest maximum growth rates with nonnutrient‐limited Scenedesmus. N‐limited Scenedesmus permitted similar growth rates at low food concentrations (below the incipient limiting level, ILL), but maximum growth rates at high food concentrations (above the ILL) were significantly reduced. With regard to the high N content of Brachionus, direct mineral N deficiency of the food appears to be possible. P‐limited algae (Scenedesmus and Cyclotella) permitted no positive growth rates of the rotifers at all. P‐limited algae that were short‐term enriched with phosphate contained similar amounts of P as nonnutrient‐limited algae but still were of lower nutritional quality, thus suggesting the importance of essential biochemical constituents.