Quantitative PCR analysis of the spatiotemporal dynamics of Aureococcus anophagefferens and Minutocellus polymorphus and the relationship between brown tides and nutrients in the coastal waters of Qinhuangdao, China

Brown tides caused by the excessive growth of the pelagophyte Aureococcus anophagefferens have occurred frequently in Qinhuangdao, China, since 2009. In this study, the temporal and spatial variations of A. anophagefferens and Minutocellus polymorphus were analyzed using real-time fluorescent quantitative PCR. The relationship between nutrient contents and brown tide events as well as the impacts of the brown tides on the composition of phytoplankton is discussed. The results showed that A. anophagefferens reached peak densities in July. Brown tides occurred in the coastal waters of Funing and Changli, and the main affected areas shifted from south to north throughout the experiment. The A. anophagefferens brown tide event was not monospecific, as M. polymorphus and Prorocentrum minimum were also observed. A redundancy analysis (RDA) indicated that decreasing concentrations of dissolved inorganic nitrogen (DIN) and increasing concentrations of the available organic nitrogen compounds (urea, dissolved free amino acids (DFAA), and dissolved combined amino acids (DCAA)) from March to June may have resulted in the outbreak of the brown bloom of A. anophagefferens, coinciding with a reduction in the community diversity of phytoplankton in the coastal waters of Qinhuangdao.