Prokaryotic community composition and structure during Phaeocystis globosa blooms in the Beibu Gulf, China

Phaeocystis globosa blooms have become one of the major ecological issues in the Beibu Gulf, China, in recent years, resulting in a series of negative impacts on local fisheries and industry. While prokaryotes play key roles in nutrient cycling and energy flow during algal blooms, information regarding the response of the prokaryotic community during Phaeocystis blooms remains scarce. Thus, a comprehensive field study covering the onset and senescent phase of P. globosa blooms was conducted in the area from December 2016 to February 2017. The community composition was revealed with high-throughput sequencing of the 16S rRNA gene. A total of 7426 operational taxonomic units (OTUs) (97% similarity) were identified from 3132328 effective tags, with Proteobacteria, Cyanobacteria, Thaumarchaeota, Verrucomicrobia, Euryarchaeota, Actinobacteria, and Bacteroidetes being the predominant taxa. The composition and structure of particle-attached (PA) and free-living (FL) prokaryotic communities were significantly different: the PA fraction was more diverse and unstable temporally compared to the FL fraction. Variations in the composition and structure of the prokaryotic community were closely associated with major environmental variables, particularly dissolved oxygen (DO), NH4+, PO43-, and dissolved organic carbon (DOC). The presence of P. globosa may result in differences in the prokaryotic community; members of Rhodobacteraceae, Alteromonadales, Porticoccaceae, Vibrio, Flavobacteriales, and Verrucomicrobiae were the key taxa in the prokaryotic communities during the outbreak and senescent phases of P. globosa blooms. This study provides primary information on the response of prokaryotic communities during P. globosa blooms and will facilitate further study on biogeochemical processes of algal-derived organic matter in the tropical gulf.