2023 Volume 59 Issue 4 Pages 49-57
Diatoms, unlike green algae and cyanobacteria, are algae that produce 20：5ω3 （EPA）, which is treated as an essential fatty acid. Since EPA is important for the survival and growth of animals, diatoms play an important role as food for zooplankton and aquatic animals in aquatic ecosystems. On the other hand, in recent years, the silica deficiency hypothesis has been proposed, and it has been reported that the outflow of silicon in rivers is decreasing. However, there are no studies evaluating the effect of decreased silicon concentration on diatom growth and EPA production at both population and individual levels.
Therefore, in this study, we conducted batch culture using the freshwater diatom Nitzschia palea with four levels of silicon concentration （5 to 30 mg/L） and investigated the effects of silicon concentration in the water environment on diatom growth and EPA production. As a result, there was no significant difference in the specific growth rate during the logarithmic growth phase, but a positive correlation was confirmed between population density and biomass （dry weight） production during the stationary phase and silicon concentration. In addition, the dry weight and shell length per cell were significantly different from those of the other systems at the lowest silicon concentration of 4.93 mg/L. EPA contents of population was significantly higher at a silicon concen tration of 29.6 mg/L than at a silicon concentration of 4.93 mg/L. EPA contents per cell was significantly higher in the silicon concentration of 4.93 mg/L than in the other systems. Therefore, it was suggested that diatoms with long shells tended to be distributed at low density in an environment with low silicon concentration, which deteriorated the food environment for consumers.
