Valley, R.D. and R.M. Newman, 1998. Competitive Interactions Between Eurasian Watermilfoil and Northern Watermilfoil in Experimental Tanks, University of Minnesota.

Reprinted with permission from Journal of Aquatic Plant Management (1998) 36: 121-126

Competitive Interactions Between Eurasian Watermilfoil and Northern Watermilfoil in Experimental Tanks

Abstract 
Two submersed macrophytes, the exotic Eurasian water milfoil (Myriophyllum spicatum L.) and the native northern watermilfoil (Myriophyllum sibiricum Kom.), were grown in 0.30-m3 outdoor experimental tanks in single- and mixed species cultures of low (75 stems m-2) and high densities (150 stems m-2). Elongation rates (cm week-1) and average individual stem and root dry mass were evaluated. Northern watermilfoil unexpectedly gained a head start because stem cuttings formed roots and began to grow before Eurasian watermilfoil cuttings were established. Still, Eurasian watermilfoil elongated much more rapidly than northern watermilfoil in all treatments (p < 0.001) and was equal in length to northern watermilfoil by the conclusion of the experi ment. Density and culture type (mixed vs single) had no effect on elongation rates. Intraspecific competitive effects on mean individual stem mass was significant in Eurasian watermilfoil monocultures (p = 0.05) and marginally significant in northern watermilfoil monocultures (p = 0.07). Stems and roots were heavier in the low-density treatments than in the high-density treatments (both p < 0.01). Interspecific competition between stems was present in the mixed-culture treatments. Given preemption, northern watermilfoil was the superior competitor. Northern watermilfoil suppressed biomass accumulation of Eurasian watermilfoil stems (p = 0.006). Biomass accumulation of northern watermilfoil was not affected when grown with Eurasian watermilfoil. In shallow, clear water, established northern watermilfoil appears to be the superior competitor, at least for biomass accumulation. These findings contrast to long-term field observations of Eurasian watermilfoil displacing northern watermilfoil. Water clarity and depth may be important factors affecting competitive interactions of Eurasian watermilfoil with other species of submersed macrophytes. 

Entire Paper
Contact: Raymond Newman, University of Minnesota, Department of Fisheries and Wildlife, 1980 Folwell Avenue, St. Paul, MN 55108-6124
Key Words: Eurasian_watermilfoil, Basic_biology, Population_dynamics
Product Type: Research, Basic_biology
User Type: Resource Management