[Annual change of phytoplankton ecological features in Fangchenggang Bay of Guangxi, South China].

In March, June, September, and December 2007, investigations were conducted on the species composition, dominant species, community structure, and abundance distribution of phytoplankton in the Fangchenggang Bay of Guangxi. Based on the investigation data, the phytoplankton abundance, biotic index, and their correlations with environmental factors were analyzed. A total of 138 species of 54 genera were identified, among which, 112 species belonged to 37 genera of diatoms, 21 species belonged to 12 genera of dinoflagellates, 2 species belonged to chrysophyta, 2 species belonged to chlorophyta, and 1 species belonged to cyanophyta. In whole year, the dominant species was Skeletonema costatum. The species number had a trend decreasing from the outer to the inner of the Bay and from spring to winter, while the cell abundance was decreased from the inner to the outer of the Bay. There was an obvious annual change in the cell abundance, being the highest (151.39 x 10(4) cells x dm(-3)) in summer (June) and the lowest (0.35 x 10(4) cells x dm(-3)) in winter (December). In spring, both the diversity and the species number were higher. Correlation analysis demonstrated that the distribution of phytoplankton community had definite correlations with water nutrient content, temperature and salinity. At the observation stations 1 and 2 in west Bay, due to the effects of Fangcheng River runoff and hydrodynamic forces such as tide, water salinity was lower and nutrient content was higher, and accordingly, S. costatum cells in summer could greatly reproduce, even result in high probability of red tide.