The similarity of carbon specific B1 uptake by picoplankton between bloom and non-bloom samples may be due to an absence of competition for assimilation of this vitamin with C. polykrikoides. Like C. polykrikoides, A. anophagefferens also displayed a larger requirement for vitamin B1 compared to B12 in culture but a lower requirement for vitamin B1 compared to B12 during blooms . Unlike B12, vitamin B1 is used in many different metabolic pathways and alternative compounds found in seawater that are not present in synthetic growth medium may be substituted by field populations.