Abstract:Phaeocystis globosa is a common harmful algal bloom species in the Beibu Gulf in recent years. As one of the areas with high frequency harmful algal blooms in Guangxi coast, there are seldom study on the P. globosa blooms in Weizhou Island. In order to investigate the status of nutrient and the effects of P. globosa blooms on phytoplankton community near Weizhou Island, a sampling survey was conducted on the area of P. globosa bloom occurred around Weizhou Island in late March 2017. The results showed that dissolved organic phosphorus (DOP) content had significantly positive correlation with the cell and colony density of P. globosa during the bloom. The bloom was mainly affected by the dissolved inorganic nitrogen (DIN), the ratio of DIN to dissolved inorganic phosphate (DIN/DIP) were lower than 10 in many stations, while the ratio of dissolved silicate to DIN (DSi/DIN) were higher than 1, indicated that nitrogen limitation existed in these areas. Nitrogen limitation was thought to be a major factor during the bloom’s demise. There were 58 species in 4 phyla of phyto- plankton identified in the survey area. The maximum abundance of P. globosa reached 1.04×108 cells/L, accounted for 98.28% of total phytoplankton. There was a significantly negative correlation between the abundance of P. globosa and the species diversity index. In addition, under nutrient deficient condition, species of diatoms with chainlike structure which were beneficial to the formation of P. globosa colony had relatively greater abundance.
