Pigment characterization of the giant colony-forming haptophyte Phaeocystis globosa in the Beibu Gulf reveals blooms of different origins

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 from September 2016 to August 2017 in the Beibu Gulf. Pigments were analyzed by high performance liquid chromatography coupled with a diode-array detector (HPLC-DAD). The pigment 19'-hexanoyloxyfucoxanthin (hex-fuco), generally considered as a diagnostic pigment for Phaeocystis , was not detected in P. globosa colonies in 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’s 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 only containing 19'-butanoyloxyfucoxanthin (but-fuco) but not hex-fuco. Using but-fuco as a diagnostic pigment, we traced two different origins of P. globosa bloom in Beibu Gulf. This study clarified the development process of P. globosa blooms in the Beibu Gulf, which provided a basis for the early monitoring and prevention of the bloom.