In addition, the ten-fold higher abundance of heterotrophic bacteria and five-fold higher picoeukaryotes likely enhances the planktonic demand for B12 during incubations since this group has been shown to be the main B-vitamin utilizers in all marine systems, surveyed to date Hence, despite the ability of C. polykrikoides to rapidly and competitively take up B12 during blooms when isolated from some ambient vitamin sources during incubations, bloom communities were likely to have quickly exhausted the B12 supply.