Effect of food conditions on the bacterial feeding of Daphnia galeata

Feeding selectivities of Daphnia galeata were measured using various density combinations of ¹⁴C-labeled Chlamydomonas and ³H-labeled natural bacteria. In all food combinations, D. galeata preferred algae. Selectivity coefficient (bacterial clearance rate: algal clearance rate) was 0.35 at the level of incipient food limitation (1.5 × 10⁶ μm³ ml^-1).However, it increased up to 0.9 with increasing total food concentration. A simple mechanical sieving model alone cannot explain such a change in the selectivity coefficient. A mechanism of 'clogging' suggestively explain the increase of bacterial ingestion efficiency by D. galeata, especially at high food concentrations. The change of selectivity coefficient related to food condition suggests that bacterial feeding by the Daphnia is incidental event associated with the algal feeding.