AUTHOR=Pan Huizhu , Xu Mingben , Lan Caibi , Ma Jixian , Li Jie , Lu Jiachang , Lai Junxiang 

TITLE=Determination of phytoplankton community structure and biomass with HPLC-CHEMTAX and microscopic methods during winter and summer in the Qinzhou Bay of the Beibu Gulf

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1186106

DOI=10.3389/fmars.2023.1186106

ISSN=2296-7745

ABSTRACT=As a typical semi-closed bay with developed aquaculture activities, Qinzhou Bay is facing environmental pressure from local fast-growing industrial and aquacultural development. Dominant species (based on microscopic examination) show a trend of miniaturization, while pico-phytoplankton (based on CHEMTAX analysis) is widely distributed in Qinzhou Bay. However, limited by scarce studies on CHEMTAX analysis, the long-term dynamic data of small-size phytoplankton are lacking in Qinzhou Bay. In this study, microscopic examination and High Performance Liquid Chromatography (HPLC)-CHEMTAX analysis were employed to characterize the spatiotemporal variability of the phytoplankton community structure in Qinzhou Bay in winter and summer of 2021. The results of microscopic observations showed that the phytoplankton community was characterized by diatoms and dinoflagellates mainly. Diatoms dominated in both seasons, of which Skeletonema costatum intensive bloom occurred in the summer. CHEMTAX analysis was not only in good agreement with microscopy data for diatoms and dinoflagellates, but also helped identification of other small-sized flagellates and cyanobacteria that hard to observe by microscope. The results of CHEMTAX analysis found that diatoms, prasinophytes and cryptophytes co-dominated the total Chl a in the winter while diatoms became the dominant group in the summer. In addition, our results are consistent with other studies and indicate that small-sized diatom became the main dominant species, and the proportion of small-sized flagellates has increased in the past decade in Qinzhou Bay, especially for cryptophytes.  Temperature, nutrient availability, and shellfish grazing pressure affected the succession of phytoplankton community from co-dominance of diatoms and non-diatoms in the winter to absolute diatoms dominance in the summer. This study enhanced our understanding of entire phytoplankton community dynamics and its relationship with environmental factors in Qinzhou Bay.