Unresolved diversity and monthly dynamics of eukaryotic phytoplankton in a temperate freshwater reservoir explored by pyrosequencing

Abstract

Environmental monitoring of the succession of phytoplankton communities in freshwater ecosystems is critical in efficient water quality management. In the present study we analysed the monthly dynamics of eukaryotic phytoplankton diversity and community structure in a freshwater reservoir (Paldang Reservoir, South Korea) using small subunit (SSU) rRNA pyrosequencing. We analysed physicochemical and biological parameters of water samples collected at monthly intervals from March 2012 to February 2013. The occurrence of phytoplankton exhibited a monthly variation: low in September (13.2%) and February (9.7%) and high in May (75.5%), July (76.5%), August (86.3%) and November (70.6%). We observed greater phytoplankton diversity predominantly represented by diatoms (37.4%), dinoflagellates (29%), cryptophytes (16%) and chlorophytes (10.4%). In early and mid-spring, diatoms, particularly Stephanodiscus spp., were dominant; however, in late spring and early summer the cryptophyte Cryptomonas spp. was dominant; the dinoflagellate Peridionopsis sp. was dominant in late summer and late autumn. Overall, the molecular results of the present study represent a typical pattern of seasonal phytoplankton succession in temperate regions. Pyrosequencing detected more phytoplankton taxa that were unresolved under microscopy, suggesting the usefulness of this method in continuous monitoring of phytoplankton communities in freshwater ecosystems.