Synechococcus bloom in the Pearl River Estuary and adjacent coastal area–With special focus on flooding during wet seasons

• Published in: The Science of the total environment 2019-11, Vol.692, p.769-783
• Main Authors: Li, Jiajun, Chen, Zuozhi, Jing, Zhiyou, Zhou, Linbin, Li, Gang, Ke, Zhixin, Jiang, Xin, Liu, Jiaxing, Liu, Huaxue, Tan, Yehui
• Format: Article
• Language: English
• Subjects: 16S rDNA; Bloom; China; Estuaries; Eutrophication; Flooding; Floods; Pearl River Estuary; Phytoplankton - physiology; Picophytoplankton; Seasons; Synechococcus; Synechococcus - physiology
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.07.088

Based on the field surveys aimed at understanding the variations of Synechococcus (Syn) abundance in the Pearl River Estuary during different seasons. We found that heavy terrestrial precipitation result in significant riverine runoffs and promote Syn growth, extension and blooms during warm and wet seasons. To understand the ecological role of Syn play in this estuary during wet seasons, we combined flow cytometry and high throughput sequencing (HTS) of 16S rDNA to investigate the phytoplankton distribution patterns and the potential shaping mechanisms during a typical wet season. During the cruise, picophytoplankton, especially Syn, and Nano-eukaryotes contributed importantly to the total phytoplankton biomass of the estuary. Syn can be further divided into phycoerythrin (PE)-rich Syn and phycocyanin (PC)-rich Syn, with PC-rich Syn about 1.5 times higher than PE-rich Syn in abundance. Both PE-rich Syn (60.75 × 103 cells ml−1) and PC-rich Syn (604.05 × 103 cells ml−1) reach the highest abundance at the lower part of the estuary. Moreover, PE-rich Syn can be divided into two subgroups which showed different salinity preference, with PE1 distributed in the high salinity area (with salinity >25) while PE2 in the middle salinity area (with salinity 7–20). Our results from the 16S rDNA sequencing also indicated abundant diversity and different niche adaptation of Syn with the operational taxonomic units (OTUs) along the estuary. Besides, analysis also indicated a tight correlation between estuarine Syn and active heterotrophic bacteria, especially groups of Rhodobacteria and Actionobacteria. [Display omitted] •Small phytoplankton, especially Synechococcus and nanoeukaryotes, contribute to the blooms in the lower Pearl River Estuary.•Phycocyanin-rich Synechococcus have wide salinity tolerances and occur in high abundance in the lower estuary.•The two groups of phycoerythrin-rich Synechococcus have different salinity tolerances.•Different niche segregation among picocyanobacterial clades can be identified from the OTUs of 16S rDNA.•Synechococcus blooms show close interactions with active bacteria, particularly for Rhodobacteria and Actinobacteria.