Population ecology of Aulacoseira granulata in Xijiang River

Aulacoseira granulata, a highlighted centric diatom, belongs to Aulacoseira, Coscinodiscaceae, Coscinodiscales, Centricae, Bacillariophyta. Through the seasonal and continuous investigation for the Xijiang River at 2009, we found that Aulacoseira granulata had four variant forms in morphology: Aulacoseira granulata var. granulata, Aulacoseira, granulata var. angustissima, Aulacoseira granulata var. curvata, Aulacoseira granulata var. angustissima f. spiralis. As an eutrophication indicator, it often got some attention because of its dominance in freshwater resources, such as rivers, lakes and reservoirs, and even in classical brackish estuary. MUller reported firstly that two types of cell valves existed in the filament chain in A. granulata at 1903, and this could promote to detect it from other Aulacoseira species. However, this finding did not attract other researchers' attention until the morphology and ecology study on this species by Kilham and Kilham at 1970s. Thus, an important epoch for A. granulata study came into being. The early studies focused on morphology and structure of filament, variationcharacteristics and population ecology. At the beginning of this century, several studies referred to toxicity of heavy metals to A. granulata and the role extracellular polysaccharide of A. granulata. Although over 100 years have past, few studies on A. granulata could be found in China, except for author's research work in the Pearl River Estuary. The Pearl River is the third large river of China and the biggest one of southern China. As the largest tributary of the Pearl River, Xijiang River is with length of 2074.8 km and basin area of 355000 km super(2). Here, the population ecology of A. granulata was studied in Xij.iang River during the whole 2009. Six sampling sites ( S1-S6 ) overlapping the main stream of Xijiang River were set to study the spatial pattern, among of them, S1-S4 sites were investigated in April and July respectively, S5 was a long-term settled site at downstream where water samples were collected every five days to study the temporal variation pattern, and S6 was set at the river estuary where water samples were collected seasonally to study the export of A. granulata from S5. Our results showed that the average proportion of A. granulata to total phytoplankton was 25.37%, and the significant positive relationship between its abundance and total phytoplankton reflected the predominant position of A. granulata in phytoplankton comm