AbstractLaboratory experiments were performed to determine the growth and grazing capabilities of two heterotrophic dinoflagellates with different feeding modes (pallium feeder: Oblea rotunda, engulfment feeder: Oxyrrhis marina) when fed with the raphidophyte Fibrocapsa japonica. Both dinoflagellates readily ingest prey and exhibit positive growth when feeding on monocultures of Fibrocapsa japonica. Maximum growth rates at food saturation were 0.54 d-1 and 0.72 d-1 for O. rotunda and O. marina, respectively. Both dinoflagellates are thus able to grow faster than their prey, for which a maximum growth rate of 0.45 d-1 has been reported. In the case of Oblea marina, it was found that a rather high food concentration of 300 Fibrocapsa cells ml-1 (corresponding to 142 µg C l-1) is needed to sustain half-saturated growth. This is consistent with the quantification of behavioural aspects of the feeding process. In about 55 % of cases, a failure to attach the tow filament after prey encounter was recorded and in about 83 % of cases, F. japonica was able to escape from the attached tow filament, indicating that motility of F. japonica represent a quite effective defence mechanism against pallium feeding dinoflagellates. In addition, qualitative observations suggest that trichocysts of Fibrocapsa may act mechanically as a grazer deterrent.