Invasive myriophyllum spicatum and nutrients interact to influence phytoplankton communities in the Portage Waterway

Document Type

Conference Proceeding

Publication Date



Eurasian watermilfoil, Myriophyllum spicatum, is a nonindigenous macrophyte that may directly compete with phytoplankton that comprise the base of aquatic food webs. We conducted a mesocosm experiment testing the effects of nutrient loading (20 μg/L P and 145 μg/L N in a 16:1 molar ratio) and presence of M. spicatum on phytoplankton communities in a full two-way factorial design (12 mesocosms, n=3 for each treatment). After 30 days, total phytoplankton biovolume was 3X greater in the nutrient-enriched mesocosms regardless of the presence of M. spicatum. Cyanobacteria such as Anabaena sp. were more common in the nutrient-enriched treatments, while attached green algae such as Cladophora and Bulbochaete spp. were more abundant in the treatments with M. spicatum. Water column chlorophyll a concentrations were highest in the nutrient treatment without plants and the lowest in the nutrient + M. spicatum treatment suggesting that the attached algaenegatively interacted with phytoplankton. In conclusion, the presence of macrophytes such as M. spicatum may enable enhanced growth of attached algae, increasing competition for nutrients and causing taxonomic shifts in the phytoplankton communities.

Publication Title

Society for Freshwater Science Annual Meeting 2015