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Since 1997, dense blooms of the alga Phaeocystis globosa have occurred in the South China Sea (SCS), and previous studies have revealed the co‐existence in this sea of two types of P. globosa cell characterized by different marker pigment profiles. However, owing to a lack of quantitative methods for the detection of different types of P. globosa cells, the dynamics of P. globosa blooms in the SCS are still poorly understood. In this study, on the basis of phylogenetic analysis of the mitochondrial atp8 (Mit atp8) gene and pigment profiles, the P. globosa strains from Pacific and Atlantic coastal waters were divided into four genotypes, of which Type I and Type IV strains co‐exist in the SCS. Furthermore, two genotype‐specific quantitative polymerase chain reaction (qPCR) methods were developed targeting the Mit atp8 gene for quantitative determinations of the densities of Type I and Type IV P. globosa cells. Both qPCR methods were reproducible, highly sensitive, and specific with a wide range of detection (from 30 to 1 × 108 cells L−1) for target P. globosa genotypes in the field, thereby facilitating the detection of low cell densities prior to bloom development, as well as high cell densities during bloom periods. Finally, the developed qPCR assays were successfully applied to determine the distribution patterns of Type I and Type IV P. globosa in the Beibu Gulf, a region of the SCS characterized by a high frequency of P. globosa blooms. [ABSTRACT FROM AUTHOR]

Brown tides of pelagophyte Aureococcus anophagefferens have been recorded in the coastal waters of Qinhuangdao in the Bohai Sea (BS) since 2009. Current understandings on the dynamics and mechanisms of brown tides in the BS, however, are still quite limited due to the lack of accurate methods for detecting low‐abundance of A. anophagefferens cells. In this study, a Taqman qPCR method was developed, which targeted 28S rDNA D1‐D2 domain of A. anophagefferens. The specificity of the qPCR method was tested using 25 strains of microalgae commonly present in the coastal waters, and the targeted species A. anophagefferens was the only species that had reliable positive signal. The method was highly sensitive and reproducible, and the lower detection limit could reach 0.3 cells of A. anophagefferens. A calibration curve was established for A. anophagefferens using the DNA template extracted from different number of cells, and the lower and upper limits of detection for the qPCR assay is 0.3 cells and 1.2 × 105 cells, respectively. A high recovery rate ranged from 96.5% to 107% was achieved for A. anophagefferens at different cell densities. The qPCR assay has been successfully applied to the study on spatial and temporal variations of A. anophagefferens in the coastal waters of Qinhuangdao in 2014. [ABSTRACT FROM AUTHOR]

Some dinoflagellate species within the generaAlexandrium,GymnodiniumandPyrodiniumare well-known producers of paralytic shellfish toxins (PST), which led to many poisoning incidents around the world. In the northern Yellow Sea, an important mariculture zone for scallopPatinopecten yessoensis, PST have been frequently detected from scallops. However, there is little knowledge concerning PST-producing microalgae in this region so far. In cruises carried out in 2011 and 2012, scallop and phytoplankton samples were collected from the northern Yellow Sea. PST were detected from scallops by high-performance liquid chromatography with fluorescence detection (HPLC-FLD). Toxin content and profile were remarkably different among the four tissues, i.e. viscera, adductor muscle, mantle and gonad, suggesting apparent toxin transfer and transformation in scallops. Viscera always had the highest content of PST dominated by low-potencyN-sulfocarbamoyl toxins C1 and C2, which closely resembled the toxin profiles of net-concentrated phytoplankton samples in spring. Based on the morphological features, cells ofAlexandriumspp. in net-concentrated phytoplankton samples were picked out and a partial sequence of the large subunit ribosomal RNA gene (LSU rDNA) was amplified using a single-cell polymerase chain reaction (PCR) method. Cells of both toxicA. tamarensespecies complex and non-toxicA. affinewere identified from the phytoplankton samples based on the partial LSU rDNA sequence information. According to these findings, it is implied thatA. tamarensespecies complex is the major toxic species related to PST contamination in scallops of the northern Yellow Sea. The presence of both toxic and non-toxicAlexandriumspp. in this region requires for a species-specific method to monitor the distribution and dynamics ofA. tamarensespecies complex. [ABSTRACT FROM AUTHOR]

The giant-colony-forming haptophyte Phaeocystis globosa has caused several large-scale blooms in the Beibu Gulf since 2011, but the distribution and dynamics of the blooms remained largely unknown. In this study, colonies of P. globosa , as well as membrane-concentrated phytoplankton samples, were collected during eight cruises in the Beibu Gulf from September 2016 to August 2017. Pigments were analyzed by high-performance liquid chromatography coupled with a diode array detector (HPLC-DAD). The pigment 19'-hexanoyloxyfucoxanthin (hex-fuco), generally considered a diagnostic pigment for Phaeocystis , was not detected in P. globosa colonies in the Beibu Gulf, whereas 19'-butanoyloxyfucoxanthin (but-fuco) was found in all colony samples. Moreover, but-fuco in membrane-concentrated phytoplankton samples exhibited a similar distribution pattern to that of P. globosa colonies, suggesting that but-fuco provided the diagnostic pigment for bloom-forming P. globosa in the Beibu Gulf. Based on the distribution of but-fuco in different water masses in the region prior to the formation of intensive blooms, it is suggested that P. globosa blooms in the Beibu Gulf could originate from two different sources. IMPORTANCE Phaeocystis globosa has formed intensive blooms in the South China Sea and even around the world, causing huge social economic losses and environmental damage. However, little is known about the formation mechanism and dynamics of P. globosa blooms. 19'-Hexanoyloxyfucoxanthin (hex-fuco) is often used as the pigment proxy to estimate Phaeocystis biomass, while this is challenged by the giant-colony-forming P. globosa in the Beibu Gulf, which contains only 19'-butanoyloxyfucoxanthin (but-fuco) but not hex-fuco. Using but-fuco as a diagnostic pigment, we traced two different origins of P. globosa blooms in the Beibu Gulf. This study clarifies the development process of P. globosa blooms in the Beibu Gulf, which provides a basis for the early monitoring and prevention of the blooms.