Effect of Bacterial Concentration on Retention and Growth Rate of the Freshwater Sponge Ephydatia fluviatilis

Abstract

Using 1-h pulse of radioactively labeled Escherichia coli, we examined, during a 24-h period, the feeding activities of Ephydatia fluviatilis in the presence of different bacterial concentrations. The results indicate an influence of the nutritional state of the sponge and the existence of a steady optimal retention rate value related to the maximal rate of phagocytosis and digestion of the sponge. These results are consistent with the measurements of sponge growth showing that bacteria can fulfill the entire food requirements of E. fluviatilis and sustain high rates of growth. The pattern of retention in relation to the bacterial concentration and nutritional state of the sponge is discussed.