Abstract
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.