FEEDING, GROWTH AND BIOLUMINESCENCE OF THE HETEROTROPHIC DINOFLAGELLATE PROTOPERIDINIUM-HUBERI

Feeding, growth and bioluminescence of the thecate heterotrophic dinoflagellate Protoperidinium huberi were measured as a function of food concentration for laboratory cultures grown on the diatom Ditylum brightwellii. Ingestion of food increased with food concentration. Maximum ingestion rates were measured at food concentrations of similar to 600 mu g C l(-1) and were similar to 0.7 mu g C individual(-1) h(-1) (1.8 D. brightwelli cells individual h(-1)). Clearance rates decreased asymptotically with increasing food concentration. Maximum clearance rates at low food concentration were ca. 23 mu l ind(-1) h(-1), which corresponds to a volume-specific clearance rate of 5.9x10(5) h(-1). Cell size of P. huberi was highly variable, with a mean diameter of 42 mu m, but no clear relationship between cell size and food concentration was evident. Specific growth rates increased with food concentration until maximum growth rates of similar to 0.7 d(-1) were reached at a food concentration of 400 mu g C l(-1) (similar to 1000 cells ml(-1)). Food concentrations as low as 10 mu g C l(-1) of D. brightwellii (similar to 25 cells ml(-1)) were able to support growth of P. huberi. The bioluminescence of P. huberi varied with its nutritional condition and growth rate. Cells held without food lost their bioluminescence capacity in a matter of days. P. huberi raised at different food concentrations showed increased bioluminescence capacity, up to food concentrations that supported maximum growth rates. The bioluminescence of P. huberi varied over a diel cycle, and these rhythmic changes persisted during 48 h of continuous darkness, indicating that the rhythm was under endogenous control.