Spatial pattern of the planktonic ciliate community and its relationship with the environment in spring in the northern Beibu Gulf, South China Sea

Surface water samples were collected from 19 sites in the northern Beibu Gulf in April 2011. Species composition and abundance of planktonic ciliates were investigated. They were combined with environmental data to obtain the spatial pattern of the ciliate community and its relationship with the environment. A total of 36 species belonging to 13 genera and 3 orders (Oligotrichida, Haptorida and Tintinnida) were identified, including 10 dominant species. All 19 samples were divided into three groups using cluster analysis and multidimensional scaling (MDS) on the basis of the ciliate species composition and abundance. Group 1 was the least abundant. The species of the order Oligotrichida dominated in Group 2. In contrast, Mesodinium species were of increased importance in Group 3. Redundancy analysis (RDA) revealed that ciliate communities were more closely related to the level of nitrogen (total nitrogen, nitrate nitrogen, nitrite nitrogen) and phosphorus (total phosphorus, active phosphorus) rather than other variables. As the levels of nitrogen and phosphorus increased, communities dominated by species from the order Oligotrichida were replaced by those dominated by Mesodinium species.