Effect of zebra mussels, Dreissena polymorpha, on stream macroinvertebrates

Zebra mussels, Dreissena polymorpha , increase macroinvertebrate abundance on hard substrata in lakes and large rivers because they enhance surface area, substratum heterogeneity and the accumulation of benthic organic matter (BOM). We tested the hypothesis that zebra mussel colonization of hard substrata in a lake-outlet stream would similarly increase macroinvertebrate abundance. Zebra mussels were attached to artificial rocks (0.05 m2) in a crossed factorial design with two states of mussels (live or dead) and three densities [low (200·m-2), medium (500·m-2) or high (1000·m-2)] plus a noncrossed control (no attached mussels). Rocks were placed in an erosional zone of a lake-outlet stream in southwestern Michigan that contained low densities of zebra mussels. After 28 d total macroinvertebrate abundance was significantly higher on rocks with high densities of zebra mussels, but live or dead treatment had no effect on macroinvertebrate abundance. Family richness differed significantly among density treatments (high = medium > low = control), but Simpson's diversity index did not differ among treatments. We conclude that changes in macroinvertebrate community structure probably were related to the increased substrate complexity provided by zebra mussels.