Food sources, ingestion and absorption in the suspension-feeding polychaete, Ditrupa arietina (O.F. Muller)

Food sources, food intake and absorption were studied for Ditrupa arietina at different periods of the year. The description of the diet was based on seasonal monitoring of fecal-pellet content produced by freshly collected w orms. The size spectrum of prey was rather large, between 1 and almost 50 m um. Throughout the year, the origin of the food was planktonic as well as b enthic. Food utilization rates were determined by radioactive pulse-chase d esign feeding experiments on four potential food sources: Skeletonema costa tum. Isochrysis galbana, Pseudoalteromonas holoplanktis and Synechococcus s p. Food intake increased linearly with food availability, except in the cas e of S. costatum. However. the threshold cell concentrations (i.e., 1 x 10( 4) and 4 x 10(4) cells ml(-1)) above which the ingestion rate of diatoms be came constant was far above the maximum concentration observed in the field . This suggests that in the bay of Banyuls-sur-Mer, the filtering capacity of D. arietina is probably not saturated by the natural concentrations of p hytoplanktonic cells. Absorption efficiencies measured for D. arietina are the first reported for a sus pens ion-feeding polychaete. These efficiencie s were in the range of values generally observed for other suspension feede rs fed on the same kind of food sources. Worms absorbed diatoms, haptophyte s, bacteria and cyanobacteria with respective efficiencies of 84.7%, 70.9%, 72.3% and 63.7%. (C) 2001 Published by Elsevier Science B.V.