Abstract
The marine benthic green macroalga Caulerpa taxifolia is an invasive seaweed found in Europe, America, and Australia, and it forms into huge algal meadows on shallow seafloors with its stolon and rhizoid systems. It has bloomed along the coast of the South China Sea, causing serious environmental problems. However, its ecological impact has not been well studied. Therefore, this study investigated the changes in concentration of NH4-N and NO2-N in artificial seawater in which C. taxifolia was cultivated under laboratory conditions during the circadian rhythm. Results showed that concentrations of NH4-N and NO2-N decreased with the increase in culture time during the circadian rhythm. In 24 h, the NH4-N-removal efficiency increased during the light period, and the maximum reached 71.4%; that of NO2-N increased with time extension in the dark period, and the maximum reached 9.2%. The absorption of NH4-N and NO2-N by terminal stolon of C. taxifolia was different. NH4-N was absorbed more preferentially than NO2-N. However, there was no obvious correlation between NH4-N and NO2-N absorption. Therefore, the terminal stolon of C. taxifolia can be used to clean up inorganic nitrogen, and showed great application potential in the remediation of eutrophic waters as the algal-bacterial symbiotic system could facilitate NO2-N removal.