ABSTRACT
Zebra mussels (Dreissena polymorpha) and quagga mussels (D. rostriformis bugensis) have changed the Great Lakes ecosystem in many ways as a result of their effects as ecosystem engineers (Karatayev et al. 2002, Zhu et al. 2006). Ecosystem engineers are organisms that alter physical, chemical, and biotic components of the ecosystem, leading to wide-scale changes that are both direct and indirect (Jones et al. 1994, 1997). Zebra mussels, rst discovered in the Great Lakes in 1986 (Carlton 2008), colonize primarily hard substrates. Benthic invertebrates associated with these hard substrates increased as a result of two changes: zebra mussels imported food to the bottom through lter-feeding material from pelagic waters and also increased structural complexity (e.g., Botts et al. 1996, Stewart et al. 1998, González and Downing 1999). The latter change can lead to decreased sh predation on invertebrates within mussel colonies (González and Downing 1999, Mayer et al. 2001, Beekey et al. 2004a).
