Effect of vitamins B1 and B12 on bloom dynamics of the harmful brown tide alga, Aureococcus anophagefferens (Pelagophyceae)

Most harmful algae require B vitamins. We investigated vitamin use by the B-1 and B-12 auxotroph, Aureococcus anophagefferens, a harmful alga that dominates plankton communities during dense brown tides'' in North America, Africa, and Asia. B-12-depleted cultures of A. anophagefferens (clone CCMP1984) adapted to lower ambient B-12 concentrations by reducing half-saturation constants (K-s) of B-12 uptake and increasing maximum uptake rates (V-max) compared to vitamin-replete cultures. In contrast, V-max of vitamin B-1 was higher in replete compared to the depleted cultures, whereas the K-s values were similar for both. K-s values for B-12 (5.0-21 pmol L-1) were similar to or higher than concentrations measured during brown tides, suggesting that B-12 may restrict the growth of this alga in the field. Over the course of a dense brown tide (> 10(6) cells mL(-1)) in Quantuck Bay, New York, vitamin B-1 and B-12 concentrations declined from > 100 pmol L-1 to < 8 pmol L-1, suggesting there was rapid uptake by A. anophagefferens and its associated microbial community. Experiments performed using radioisotope-labeled vitamins B-1 and B-12 and C-14-bicarbonate indicated that plankton in the size range of A. anophagefferens (1-5 mu m) were responsible for the majority of primary production and the majority of vitamin B-1 uptake but shared vitamin B-12 uptake with smaller picoplankton (< 1 mu m). Vitamin uptake rates during the brown tide were capable of turning over standing stocks of vitamin B-12 in 15 h, whereas B-1 depletion was slower with maximal turnover times of 2.8 d. As the brown tide intensified and vitamin B-12 levels declined, the experimental enrichment of brown tide water with vitamin B-12 significantly enhanced the growth rates of A. anophagefferens. Collectively, this study demonstrates that vitamin B-12 can influence the intensity of harmful algal blooms caused by A. anophagefferens.