Diatoms are a primary producer and play an important role in the functioning of microbial food webs. Temporal variations in community patterns of planktonic diatom assemblages were studied during a 1-year cycle (June 2007–May 2008) in Jiaozhou Bay, northern China. Samples were collected biweekly at a depth of 1 m from five sampling stations. A total of 75 diatom species representing 40 genera, 28 family, 19 orders and three classes were recorded. Of these species, 11 distributed in all four seasons, while 27, 35, 56 and 28 forms occurred only in spring, summer, autumn and winter season, respectively. The species number and total abundance peaked in autumn, with minimum values in May. All three species biodiversity measures (Shannon diversity, Pielou's evenness and Marglef's richness) peaked in spring and autumn. There was a significant difference in diatom community patterns among seasons, except the pair of spring and winter. The environmental variables, especially temperature and the nutrients, could significantly drive the seasonal variation in diatom community patterns. Of 11 dominant species, four (Paralia sulcata, Skeletonema costatum, Guinardia delicatula and Nitzschia lorenziana) were significantly related with temperature, pH and/or nutrients. These findings suggest that the seasonal shift in community pattern of planktonic diatoms was driven by both temperature and nutrients in this eutrophic basin ecosystem.

To reveal the annual patterns of planktonic ciliate communities, planktonic ciliate species composition, abundance and biomass, and responses to environmental conditions, were investigated during an annual cycle in Jiaozhou Bay, Qingdao, northern China. A total of 64 species belonging to five orders (Oligotrichida, Haptorida, Cyrtophorida, Hypotrichida and Tintinnida) were identified, 9 of which were dominant. Ciliate communities presented a clear seasonal pattern in terms of both abundance and biomass. A single peak of ciliate abundance and biomass occurred in late August, mainly due to the oligotrichids, tintinnids and haptorids. The 9 dominant species showed a distinct temporal distribution with seasonal successions of ciliate communities. Multivariate analyses revealed that ciliate abundance was significantly correlated with water temperature, dissolved oxygen and nutrients, especially nitrate nitrogen and soluble reactive phosphate (P < 0.05). These findings provided basic data on annual cycle of planktonic ciliate communities in a semi-enclosed bay of Yellow Sea, northern China.