Respiration and ingestion rate of different sized Daphnia pulex fed on four algal species

Abstract

Respiration rate and ingestion rate for four different algal species (Scenedesmus quadricauda, Asterionella formosa, Aphanizomenon flos-aquae and Planktotrix rubescens) of different sized Daphnia pulex were measured in the laboratory. Population of D. pulex grew maximally when it fed S.quadricauda, but the presence of P. rubescens and A. flos-aquae caused negative population growth rate. Ingestion rates increased with increasing body size for all in- vestigated algae; the lowest b value was obtained for S. quadricauda and the highest one for P. rubescens. The amount of ingested carbon exceeded the required amount for standard metabolism in both small and large sized individuals fed all four algal species. Relatively higher amount of ingested A. flos-aquae and P. rubescens in comparison with A. formosa and S. quadricauda and the results of the growth experiments indicate that the inhibitory effect of filamentous blue-green algae on D. pulex is more due to toxicity, low assimilation efficiency or/and inadequate composition than incapability of ingestion due to mechanical interference with filaments.