Macrophyte-macroinvertebrate interactions in a lentic ecosystem and the effect of fluridone treatment to control Myriophyllum spicatum L.

Myriophyllum spicatum L. is an exotic macrophyte that can become pestiferous in lentic ecosystems. Two field studies were conducted to investigate: 1) epiphytic macroinvertebrates associated with M. spicatum and native macrophytes; and 2) epiphytic macroinvertebrate community response to fluridone treatment for M. spicatum control. In the first study evaluating epiphytic macroinvertebrates associated with M. spicatum and native macrophytes, triplicate samples were collected at three sites in both Auburn and Zumbra Lakes, Minnesota, USA. One site in each lake contained primarily M. spicatum, the second site contained M. spicatum and native vegetation, and the third site was dominated by native vegetation. Mean macroinvertebrate taxa richness, total density and biomass were significantly higher in Auburn Lake than at corresponding sites in Zumbra Lake on most dates. Several significant differences in mean epiphytic macroinvertebrate taxa richness, total density and biomass were observed among the sites within both Auburn and Zumbra Lakes. However, these differences followed no apparent trend suggesting that epiphytic macroinvertebrates do not selectively colonize any of the macrophyte assemblages studied in Auburn or Zumbra Lakes. The second study evaluated the secondary effects of fluridone treatment for M. spicatum control on epiphytic macroinvertebrate communities. Sites in Zumbra Lake, Minnesota were compared before and after fluridone application. One site contained predominantly M. spicatum, the second contained a mixture of M. spicatum and native vegetation, and the third possessed predominantly native vegetation. Triplicate macroinvertebrate samples were taken at 1 and 2 m depths at each sample site. Samples were taken before treatment in July, August and September, 1993, and after the May 23, 1994 fluridone treatment (24 µg/L) in July, August and September, 1994 and 1995. Following herbicide application a decrease in macrophyte species richness and biomass at each site was associated with significant decreases in epiphytic macroinvertebrate mean taxa richness, densities and biomass