Aims: To evaluate the influence of marine bacterial assemblages from the Bay of Fundy on Alexandrium fundyense str. CB301 growth. Methods and Results: Bacterial assemblages were collected from the Bay of Fundy during an Alexandrium spp. bloom, serially diluted to extinction and inoculated into axenic CB301 cultures. Bacterial assemblages dramatically enhanced CB301 growth. Retrieval and analysis of 16S rDNA fragments revealed an Alteromonas sp. strain to be the only detectable bacterium in all assemblages that promoted A. fundyense and the sole bacterium found in the most dilute inoculum that promoted. A. fundyense. While this bacterium has not yet been isolated, other isolates obtained from the assemblages did not stimulate A. fundyense, indicating that the observed stimulation was not a general effect of marine bacteria. Conclusions: Bay of Fundy marine bacterial assemblages dominated by a member of the family Alteromonadaceae were found to dramatically stimulate growth of A. funalyense. Significance and Impact of the Study: These results show that native bacteria have the potential to dramatically promote the growth of A. fundyense and may play an important role in influencing A. fundyense dynamics in the Bay of Fundy.