The relationship between Dreissena and infaunal taxa may not be simple. Some species may be positively affected by Dreissena, while others are negatively affected (Karatayev et al. 1997). In a Belarussian study, benthic invertebrate biomass in Lukomskoe Lake was eight times greater in druses (clumps of attached zebra mussels), even though densities were 1.5 times lower than in sandy sediments. This was because the communities within the druses consisted of larger species (Karatayev et al. 1983). Dusoge (1966) found that the abundance of benthic invertebrates in Mikolajskie Lake (Poland) positively correlated with zebra mussel abundance. According to Afanasiev (1987), there were positive correlations between zebra mussel biomass and the density of some oligochaetes in the cooling reservoir of a power plant (Ukraine), but for others he found no correlation or negative correlation. Wolnomiejski (1970) reported that Dreissena provide substrate or shelter for many benthic taxa including the isopod, Asellus aquaticus, larval chironomids, Microtendipes gr. chloris and Limnochironomus gr. nervosus, and the leech, Helobdella stagnalis. Wiktor (1969) found that benthic biomass near colonies ofDreissena was twice that found elsewhere. Karatayev and Lyakhnovich (1990) found that crustaceans Asellus aquaticus and Gammarus lacustris at depths over 2 m were only found with Dreissena.
In North America, zebra mussels appear to have similar effects on benthic communities (Stewart and Haynes 1994, Wisenden and Bailey 1995, Botts et al. 1996). Wisenden and Bailey (1995) found the density and taxonomic richness of macroinvertebrates in Lake Erie directly correlated with zebra mussel densities. Botts et al. (1996) compared the density of benthic invertebrates in bare sand and in sand associated with zebra mussel druses in Lake Erie. In a survey, they found that the densities of amphipods, chironomids, oligochaetes, turbellarians, hydrozoans, and the total invertebrate density were significantly higher in sand with druses than in bare sand. In an experiment with mesh bags containing either living druses, artificial druses made from cleaned zebra mussel shells, or no zebra mussels, they found that chironomids were significantly more abundant in living druses than in nonliving druses. There were no significant differences in oligochaetes among all three treatments.