The absence or low relative abundance of 177R, 269Y, 160R and 272Y in bloom samples may indicate either toxic or allelopathic inhibition of these organisms by C. polykrikoides. T-RFs 290Y and 180R, which were more abundant in bloom than non-bloom samples (total and >5 mm size fractions respectively), were consistent with those predicted from 16S rRNA sequences of alpha-Proteobacteria, and may represent organisms closely associated with or promoted by C.polykrikoides