Do quagga mussels colonize deeper waters than zebra mussels?
D. r. bugensis lacks the keeled shape that allows D. polymorpha to attach so tenaciously to hard substrata; though, D. r. bugensis is able to colonize hard and soft substrata (Mills et al., 1996). The ability to colonize different substratas could suggest that D. r. bugensis is not limited to deeper water habitats and that it may inhabit a wider range of water depths. In the Great Lakes, there are reports that the quagga mussel is colonizing at shallower depths, supporting the idea that the quagga can occupy a wider range of depths (Mills et al., 1996). Quagga and zebra mussels have been found to coexist at lower depths in Lake Ontario, but in Lake Erie as the water depth increased D. r. bugensis outnumbered D. polymorpha 14 to 1, suggesting that this species is a cold-water form of dreissenid (Mills et al., 1996). Dreissena rostriformis bugensis has been found at depths up to 130 m in the Great Lakes, but is only known to exist in its native range from depths 0-28 m and the depths at
