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Prey selectivity, growth and feeding responses were studied in the cillate Balanion comaturn (17 pm) and the heterotroph~c dinoflagellate Gjmnodinium sp. (7 pm). Almost identical prey size spectra were found for the 2 organisms. Optimum prey size was 8 pm, while the lower and upper hmits of prey capture were -4 and 10 pm, respectively. Maximum growth and ingestion rates of B. comatum were slightly higher than those of Gj~mnodinium sp. Threshold prey concentration for growth of B. comatum and Gymnodinium sp. was 11 and 17 pg C I-', respectively. At 15"C, both organisms needed to ingest approx. 1 to 2 % h-' of their cell volume in order to sustain basic metabolic actlvlty. M a x ~m u m specific clearance was 2 to 3 tlmes h ~g h e r for the ciliate compared to the dinoflagellate. Gymnodlnium sp. survived for a longer time than B. comatum when deprived of prey organisms. Gymnodinium sp. cells were not ingested by B. comatum, although they were of a size which is optimal for B. comatum.
Jakobsen et al. (Wed,) studied this question.