Epiphytic macroinvertebrate communities on Eurasian watermilfoil (Myriophyllum spicatum) and native milfoils Myriophyllum sibericum and Myriophyllum alterniflorum in eastern North America

Aquatic macrophytes play an important role in the survival and proliferation of invertebrates in freshwater ecosystems. Epiphytic invertebrate communities may be altered through the replacement of native macrophytes by exotic macrophytes, even when the macrophytes are close relatives and have similar morphology. We sampled an invasive exotic macrophyte, Eurasian watermilfoil ( Myriophyllum spicatum ), and native milfoils Myriophyllum sibericum and Myriophyllum alterniflorum in four bodies of water in southern Quebec and upstate New York during the summer of 2005. Within each waterbody, we compared the abundance, diversity, and community composition of epiphytic macroinvertebrates on exotic and native Myriophyllum. In general, both M. sibericum and M. alterniflorum had higher invertebrate diversity and higher invertebrate biomass and supported more gastropods than the exotic M. spicatum. In late summer, invertebrate density tended to be higher on M. sibericum than on M. spicatum, but lower on M. alterniflorum than on M. spicatum. Our results demonstrate that M. spicatum supports macroinvertebrate communities that may differ from those on structurally similar native macrophytes, although these differences vary across sites and sampling dates. Thus, the replacement of native milfoils by M. spicatum may have indirect effects on aquatic food webs.