The structure and distribution of phytoplankton community in the Qinzhou Bay during dry season

Photosynthetic pigment analysis method was used to analyze the structure and distribution of phytoplankton community in the Qinzhou Bay in the dry season of 2011. Data showed that the major phytoplankton pigments were chlorophyll a, fucoxanthin, chlorophyll b, prasinoxanthin and peridinin, while the levels of other photosynthetic pigments were very low. Bacillariophyta, Prasinophyceae and Dinoflagellates were detected as dominant phytoplankton groups during the dry season by converting signal changes into phytoplankton spectra-dynamics with CHEMTAX software. The mean biomass of three groups phytoplankton were (2.36±2.38) μg/L, (0.87±0.53) μg/L, and (0.13±0.14) μg/L, ranging from 0.18 μg/L to 7.45 μg/L, from 0.10 μg/L to 1.80 μg/L, and from 0.02 μg/L to 0.60 μg/L, respectively. The Bacillariophyta, Prasinophyceae and Dinoflagellates occupied the total biomass of phytoplankton by 59%±21%, 30%±16% and 6%±4%, ranging from 29% to 96%, 1% to 53% and 0.4% to 53%, respectively. Bacillariophyta dominated in the Maolingjiang Estuary and its adjacent areas, while both Bacillariophyta and Prasinophyceae dominated in the inner and outer bay areas. The community structure and distribution of the phytoplankton were influenced by river floods, salinity, and nutrients. Large-scale oyster aquaculture might lead to decrease of Bacillariophyta ratio in inner and outer bay areas, while increased water temperature in the outer bay might make Bacillariophyta largely grow and be the dominant group. The diatom red tide might occur under the condition of further increase in temperature and nutrient input.