Allelopathic Inhibition Effects of Myriophyllum spicatum on Growths of Bloom-Forming Cyanobacteria and Other Phytoplankton Species in Coexistence Experiments

Many studies have attempted to find measures for control of cyanobacterial harmful algal blooms (cyanoHABs) caused by Microcystis, Anabaena, and other bloom-forming plankton species. We have investigated allelopathic inhibition of the submerged macrophyte Myriophyllum spicatum on four phytoplankton species of two taxonomic groups: Chlorophyta Selenastrum capricornutum, Scenedesmus obliquus, and cyanobacteria Microcystis aeruginosa (different strains for toxic, non-toxic, the North Han River originated (NHR) and colonies) and Anabaena circinalis. Inhibitions of unicellular cyanobacteria M. aeruginosa were over 50% for three consecutive days from the 3rd to the 5th day of the coexistence. M. spicatum even inhibited M. aeruginosa at a high initial concentration (1.1 mg L−1 Chl-a). Moreover, M. aeruginosa in a mixture of four phytoplankton species (S. capricornutum, S. obliquus, M. aeruginosa and A. circinalis) was selectively inhibited by M. spicatum. The inhibition of toxic, non-toxic, and NHR of Microcystis by M. spicatum were not significantly different. Colonial cyanobacteria strains were mostly not inhibited by M. spicatum.