Abstract
Artificial circulation potentially causes the succession of a phytoplankton community through complex mechanisms in hydraulic and ecological prosseses. In order to clarify the effect of tolerance against prolonged darkness on the community succession, the dark survival was studied for three phytoplankton taxa, Microcystis aeruginosa (Cyanobacteria), Scenedesmus quadricauda (Chlorophyceae), and Melosira ambigua (Bacillariophyceae). The period of darkness was varied by 5 cases, such as 5days, 10days, 15days, 20days and the control. Thereafter, all samples were reilluminated.
In the cases of more than 10days of darkness M. aeruginosa decreased more markedly with the darkness period, and became only 1% of the initial cell number in 20day darkness period. Whereas, S. quadricauda and M. ambigua remained their biomass even with the 20day dark period. After restarting the light-dark cycle, however, all the three species similarly increased exponentially and reached the maximum biomass levels. These results suggest that the different tolerance against prolonged darkness may cause the succession of phytoplankton community in the process of artificial circulation.
