Kinetics and energetics of growth of the marine choanoflagellate Stephanoeca diplocostata

Growth klnetics and energetics of the marine, loricate choanoflagellate Stephanoeca diplocostata Ellis were investigated in batch cultures at a temperature of 18C. The increase of cell numbers was exponential, with no evidence for a lag phase upon subculturing from a growing culture into a fresh bacterial suspension. Subculturing from a stationary phase culture resulted in lag phases of up to 24 h. A maximum growth rate of 1.9d-' was observed at a bacterial concentration of about 10' bacteria ml-l. The half saturation constant for growth was 6 . 8 ~ 106 bacteria ml-' Growth rate decreased to less than 0.5d-' at a concentration of 2.5 X 106 bacteria ml-l. Of the bacterial organic carbon ingested by S. diplocostata, it was estimated that 60 O/O was used in respiration, 13 ' 1 0 was egested as unassimilated particulate organic matter and 27 % was used for growth.