Seasonal variation in functional phytoplankton groups in Xiangxi Bay, Three Gorges Reservoir

We describe the phytoplankton dynamics and structure in Xiangxi Bay, Three Gorges Reservoir. Samples were collected monthly in the surface waters between August 2007 and July 2008. We identified 10 principle functional groups. C-strategists and S/R-strategists with a wide range of tolerance dominated the phytoplankton assemblage. Seasonal variation was related to water column stability because of changes in hydraulic operation in October, January, and May. Functional group C (Asterionella formosa) and P (Aulacoseria granulata) dominated in August and September, whereas group Lo (Peridiniopsis niei) was the most abundant between February and April, forming a dinoflagellate bloom. Group B (Stephanodiscus hantzschii), X2 (Komma acudata), and Y (Cryptomonas erosa) were present throughout most of the year but were most abundant in late spring. A cyanobacterial bloom occurred from June to July, during which group M (Microcystis aeruginosa, M. wesenbergii) and H1 (Anabaena flos-aquae) were dominant. Green algae, characterized by group G (Eudorina sp., Pandorina sp., Pyramidomonas sp.) and J (Pediastrum spp., Coelastrum spp., Scenedesums spp.), were abundant after the bloom degraded. This sequence was corroborated by canonical correspondence analysis (CCA). The summary sequence of functional groups resulting from CCA was: C/P -> Lo -> H1/M/J/G. The dynamics of the phytoplankton community may be explained by the stability of water column, irradiance, water temperature, and nutrient structure.