Growth and grazing by the thecate heterotrophic dinoflagellate Diplopsalis lenticula (Diplopsalidaceae, Dinophyceae)

The thecate heterotrophic dinoflagellate Diplopsalis lenticula Bergh was shown to feed on a wide range of phytoplankton of different size and taxonomic groups. Growth and ingestion rates of D. lenricula feeding on the diatom Ditylum brightwellii (West) Grunow were measured as a function of food concentration. Growth rate increased with food concentration until it reached saturation at c. 300 D. brightwellii cells ml−1. Maximum specific growth rate was 0.25 d−1 at a food concentration of 500 cells ml−1. A prey concentration as low as 30 cells ml−1 supported growth. Ingestion and clearance rates were estimated by two different methods based on estimates of prey loss rate and on counts of digested food particles. Ingestion rate increased with increasing food concentration up to a maximum rate of 1 or 0.2 prey dinoflagellate−1 h−1, depending on which of the two methods of estimation was used. Clearance rate decreased with increasing prey concentration. Maximum clearance rates at low food concentration were 2.7 and 1.2 μl dinoflagellate−1 h−1, corresponding to volume-specific clearance rates of 1.5 × 105 and 6.4 × 104 h−1, respectively.