Dynamics of Phaeocystis globosa bloom and implications for its seed sources in the Beibu Gulf, China

Algal blooms of haptophyte Phaeocystis globosa have been recorded in the Beibu Gulf,South China Sea(SCS) since 2011. Recent evidence suggests that Type Ⅰ and Type Ⅳ are the two dominant genotypes of P. globosa coexisting in this area, and their marker pigment profiles, colony sizes, and genetic information differ. Two genotype-specific quantitative polymerase chain reaction(qPCR) assays were used to clarify the distribution and dynamics of P. globosa bloom in the Beibu Gulffrom November 2018 to February 2019. Results show that the patterns of spatial-temporal distribution of Type Ⅰ and Type Ⅳ were similar, the abundance of Type Ⅳ was higher than that of Type Ⅰ during the algal bloom, and thus Type Ⅳcells dominated the P. globosa bloom in winter 2018. The relationships between environmental factors and P. globosa abundance indicated that temperature and nitrate were critical to the distribution and dynamics of P. globosa blooms in this area. The distribution of P. globosa cells in different water masses before the bloom revealed that the westward water via the Qiongzhou Strait, the SCS bottom water, and the current in the northwestern waters of Hainan Island could transport P. globosa cells into the Beibu Gulf serving as the seed sources triggering the intense blooms in the Beibu Gulf.