No evidence of an allelopathic effect of Eurasian watermilfoil (Myriophyllum spicatum) on cyanobacteria in two Canadian Lakes

Abstract

Eurasian watermilfoil (Myriophyllum spicatum) is an exotic vascular plant in North America and highly invasive in lacustrine environments. This plant forms dense, extensive beds that can interfere with recreational activities. Eurasian watermilfoil has been shown in laboratory experiments to cause mortality or low growth rates to several species of cyanobacteria, because of allelopathic molecules (fatty acids, polyphenols) released into the water by the plant. The allelopathic effect of Eurasian watermilfoil has never been studied in a natural setting. The main objective of this study was to verify whether a causal link between Eurasian watermilfoil and cyanobacteria could be established in two infested lakes of southern Québec, Canada. Some fatty acids or polyphenols (ellagic, nonanoic, octadecenoic and oleic acids) were detected in summer and autumn in the water, but in concentrations well below (30 to 35,000 times lower) the theoretical concentrations at which they reduce the growth of cyanobacteria. There was no evidence of allelopathic effects of Eurasian watermilfoil on the cyanobacterial assemblages. Other chemical and physical factors likely had greater influences on cyanobacterial assemblage composition than Eurasian watermilfoil, notably phosphorus concentration and water temperature. However, some cyanobacterial species known to be influenced by Eurasian watermilfoil, in particular Microcystis aeruginosa, were not specifically identified in this study, so caution must be exercised before concluding that there is no allelopathic effect.

Keywords

• Allelopathy
• Eurasian watermilfoil
• fatty acid
• lake
• Microcystis aeruginosa
• Myriophyllum spicatum