The Effects of Zebra Mussel (Dreissena polymorpha) Colonization on the Macroinvertebrate Community of a Third Order Stream
Hasfurther, Debra L.
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Dreissena polymorpha, or the zebra mussel, invaded U.S. waters In approximately 1985 and has since experienced an explosive growth in population. This tiny bivalve has virtually taken over large portions of the Great Lakes and threatens to over-colonize and outcompete native organisms in every waterway in the northern United States. With predictions of heavy colonization over the coming years, significant efforts have been launched not only to control the zebra mussel but also to assess the impact it will have on other organisms. Due to the fact that zebra mussels out-compete many species for precious nutrients in the water column and also disturb breeding grounds , for some species of fish, it is assumed that they will create harmful effects for many native species. However, D. polymorpha is also an efficient biofilterer, rapidly cleaning up any water system it inhabits, and provides ideal shelter for many macroinvertebrates. At this point it is difficult to assess the relationship between costs and benefits that colonization of this species may provide. In this experiment we discovered that in the presence of dead zebra mussels, invertebrate families Tricladidae, Hydropsychidae, and Hydrobiidae as well as the total number of invertebrates flourished as they were able to make use of the protective shells for shelter while not experiencing feeding competition. Moreover, nearly all families of invertebrates included in this study also experienced an increase in establishment when live mussels were present. This pattern indicates that the benefit of shelter and increased surface area created by the presence of the mussels outweighed any negative impact produced by competition. Other invertebrate families showed no overall change in establishment ability between substrate completely free of mussels, with a low density of mussels, a high density, or with only dead zebra mussels. These families suffered no negative impact or benefit as a result of the colonization of the zebra mussel invader.