Comparison of nutrient and microbial dynamics over a seasonal cycle in a mid-Atlantic coastal lagoon prone to Aureococcus anophagefferens (brown tide) blooms

To determine the roles of dissolved organic matter in the onset, duration, and decline of blooms of the "brown tide" pelagophyte, Aureococcus anophagefferens, nutrient and microbial dynamics, heterotrophic and autotrophic carbon (C) and nitrogen (N) uptake, and peptide hydrolysis were compared in natural populations: (1) seasonally, among physically similar sites in a mid-Atlantic coastal lagoon, Chincoteague Bay, (2) at an individual site as a bloom initiated, developed, and declined, and (3) in whole versus size-fractionated water. Throughout the year, urea was the dominant form of N taken up at both bloom and nonbloom sites. C acquisition in the A. anophagefferens (1.2-5.0 μm) size fraction was dominated by bicarbonate uptake during bloom initiation but organic C compounds were taken up later during and after the bloom. Bacterial productivity was enhanced during and just after the bloom and bacterial abundance was four times higher at the bloom versus nonbloom site.