Primary production rates inside the bloom patches were some of the highest observed in eastern Long Island estuaries , rivaling those observed during high biomass blooms of the brown tide-forming Aureococcus anopha-gefferens . Interestingly, the picophytoplankton were responsible for approximately 20–25% of carbon fixation in both bloom and non-bloom samples , though cyanobacteria were likely more important primary producers outside patches and while picoeukaryotes were likely larger contributors inside (Fig. 3). The high rates of carbon-specific primary production in the >20 mm size fraction and the high levels of dissolved oxygen within patch communities were consistent with what has been previously observed in Chesapeake Bay . This suggests that during the day, despite its phagotrophic abilities, C. polykrikoides obtained much of its cellular carbon via photosynthesis. It is important to note that photosynthetic rates may be a slight overestimate since the two hour incubation typically occurred between 1200 and 1400 EDT and the resulting calculation does not account for the slightly lower photosynthetic rates which likely occur during the morning and evening hours. The recent revelations that harmful algae have a much higher incidence of vitamin auxotrophy than other phytoplankton , that vitamins can enhance the chain length of C. polykrikoides , and that vitamin B12 can influence brown tides formed by A. anophagefferens have all added vitamins to the list nutritional factors that may contribute to the formation of HABs. Previous studies have shown that vitamin B12 utilization is dominated by the picoplankton , even during algal blooms , with multiple lines of evidence suggesting heterotrophic bacteria are the primary vitamin users . In contrast, during C. polykrikoides blooms B12 utilization occurred primarily in larger plankton (>2 mm; 64.4 _ 7.10%; Suppl. Table 1) suggesting that C. polykrikoides is better able to gain access to the pM concentrations of vitamins than other phytoplankton, including A. anophagefferens, and bacteria .