Impacts of Dreissena on Benthic Macroinvertebrate Communities

............................................................................................................................................................................... 599 Introduction .......................................................................................................................................................................... 599 Mechanisms of Impacts: Filtration and Substrate Alteration .............................................................................................. 600 Impacts on Macroinvertebrate Abundance, Diversity, and Composition ............................................................................ 601 Impacts on Native Bivalves .................................................................................................................................................. 603 Predictors of Dreissena Impact ........................................................................................................................................... 604 Temporal Variability of Impact ........................................................................................................................................... 605 Conclusions and Future Research Directions ...................................................................................................................... 605 Acknowledgments ................................................................................................................................................................ 606 References ............................................................................................................................................................................ 606 600 Quagga and Zebra Mussels: biology, iMpacts, and control important in freshwater ecosystems as mediators of nutrient cycling and energy flow (Covich et al. 1999); and (3) an essential food resource for higher consumers (Vander Zanden and Vadaboncoeur 2002, Schummer et al. 2008). Indeed, changes in the composition and abundance of benthic macroinvertebrates can alter the diet and condition of fish (Owens and Dittman 2003, McNickle et al. 2006). Moreover, accurate models to predict impacts are needed to ensure that observed changes caused by Dreissena are not mistakenly attributed to watershed management schemes (e.g., phosphorus abatement) and other environmental stressors, such as contaminants and climate change (MacNeil and Briffa 2009, Atalah et al. 2010). MeChANISMS OF IMpACTS: FILTRATION AND SUBSTRATe ALTeRATION Dreissena can alter benthic macroinvertebrate communities in lakes and rivers through a variety of mechanisms, but most directly through physical alteration of substrates (Figure 38.1). Like their marine relatives (Suchanek 1986, Lohse 1993), zebra and quagga mussels form dense aggregations (clumped shells of live and dead individuals) by attaching to substrates and to each other’s shells with byssal threads; these aggregations provide colonizable surfaces for algae and structurally complex habitat for macroinvertebrates (Ricciardi et al. 1997, Stewart et al. 1998a). Interstitial spaces between mussel shells passively trap sediments and are used by smaller invertebrates as refugia from predation and environmental stressors such as wave action (Gutiérrez et al. 2003, Beekey et al. 2004, Reed et al. 2004). Although common in coastal marine systems where byssally attached molluscs abound (Suchanek 1986), this type of habitat engineering was nonexistent in European and North American freshwater habitats prior to colonization by Dreissena. Dreissenid mussels link offshore planktonic and nearshore benthic communities by filtering suspended particles from the water column and depositing the material as mucus-bound feces and undigested pseudofeces (Karatayev et al. 1997, Gergs et al. 2009). This link has been referred to as the pelagic-to-benthic shunt because it reduces available planktonic resources and increases the organic content of sediments surrounding dreissenid mussel beds (Karatayev et al. 1997, Stewart et al. 1998a, Hecky et al. 2004). Mussel