Distribution and population dynamics of cryptomonads in a C hinese lake with three basins varying in their trophic state

Summary Cryptomonads are unicellular algae that are important primary producers in various aquatic ecosystems. However, their ecological importance was often neglected owing to their brittleness. Their population in freshwater was thought to be regulated mainly by grazing pressure, and the effects of lake trophy were less important. In this study, the cryptomonad species in three basins of L ake D onghu, a shallow lake in C hina were identified, and their distribution, seasonal dynamics, and relationships with several environmental factors were investigated. Eight cryptomonads were identified at species level by morphological examination; species belonging to the genera K omma and C ryptomonas were most common. Cryptomonads displayed inconsistent distribution and population dynamics among the three basins of different trophic status. They were the dominant species in the eutrophic basin, while their proportion was lower in the hypertrophic basin and in the mesotrophic basin. The biomass of cryptomonads was highest in the hypertrophic region. As a whole, cryptomonads kept low biomass during winter, while rapid waxing and waning of their population was observed in the other seasons. Cryptomonads species exhibit distinct seasonal trends. Canonical correspondence analysis revealed water temperature and dissolved total nitrogen were the most important factors that affected the composition of the cryptomonads community. Spearman correlation analysis demonstrated that the biomass of cryptomonads was positively correlated with pH value, dissolved total nitrogen and dissolved organic carbon. In conclusion, lake trophy is a crucial factor affecting the total cryptomonads population.