Partitioning of the food ration of marine ciliates between pico- and nanoplankton

Food size-range for 13 species of Tintinnina and 18 species of Oligotrichina were studied using electronic particle counting and in situ observation of food vacuole contents. Tintinnids consume nanoplankton in the size range 2-20 mu m. Oligotrichous naked ciliates consume particles in the size range 0.5-10 mu m. Ciliates smaller than 30 mu m take 72% picoplankton and 28% nanoplankton. For ciliates between 30 mu m and 50 mu m the proportions are reversed (30% pico- and 70% nanoplankton), while the larger ciliates (> 50 mu m) take nanoplankton almost exclusively (95% nano- and 5% picoplankton). A seasonal study of total Oligotrichida grazing showed that natural particles were consumed at rates that varied from 1 to 20 mu g C/l/day. This included between 1 and 38% of the bacterioplankton production and 9 to 52% of the nanoplankton production. In the N-W Mediterranean the total ciliate production varied from 0.4 to 8.2 mu g C/l/day. (DBO)