Inter-annual and seasonal variations of phytoplankton community and its relation to water pollution in Futian Mangrove of Shenzhen, China

Inter-annual and seasonal variations of a phytoplankton community over a 5-year period (2008-2012) were studied in Futian Mangrove in Shenzhen, China, in relation to the influence of water pollution. A total of 324 phytoplankton taxa belonging to 8 phyla were identified, of which 233 were Bacillariophyta, followed by 50 Chlorophyta, 18 Cyanophyta, 11 Pyrrophyta, 6 Euglenophyta, 3 Cryptophyta, 2 Xanthophyta, and 1 Chrysophyta. The abundance of phytoplankton ranged from 3.86 × 104 to 5.20 × 108 cells/L and averaged 1.94 × 107 cells/L. Phytoplankton diversity fluctuated seasonally and inter-annually, and species numbers showed a decreasing tendency from 124 species in 2008 to 89 species in 2012. Phytoplankton was numerically dominated by Cyclotella atomus, Conticribra weissflogii and Skeletonema spp. with relative abundance of 42%, 22.8% and 15.8%, respectively. Phytoplankton community changed with the variation of physicochemical factors. Results of canonical correspondence analysis showed that physicochemical variables, including total phosphate, temperature and salinity, were the most important factors influencing the variation of phytoplankton community structure. It is suggested that sewage flow found in the mangrove is the most plausible explanation for increased pollution, as indicated by the higher phytoplankton abundance, the presence of such pollution indicative phytoplankton species as C. weissflogii and C. atomus, and hence, the decrease in phytoplankton species from 2008 to 2012.