Zebra versus quagga mussels: a review of their spread, population dynamics, and ecosystem impacts

Abstract

Dreissena polymorpha (zebra mussel) and D. rostriformis bugensis (quagga mussel) continue to spread in Europe and in North America, and have large ecological and economic impacts where they invade. Today many more waterbodies are invaded by zebra mussels, and therefore the extent of their impact is greater than that of quagga mussels. Both species provide additional space and food for invertebrates in the littoral zone, increasing their diversity and density. In contrast, in the profundal zone, quagga mussels may compete for space and food resources with benthic invertebrates, decreasing their diversity and density. The system-wide effect of dreissenids depends on water mixing rates, lake morphology, and turnover rates. Because quagga mussels are found in all regions of a lake, and form larger populations, they may filter larger volumes of water and may have greater system-wide effects, especially in deep lakes, than zebra mussels, which are restricted to shallower portions of lakes. Shortly after initial invasion, as populations increase, both dreissenids will have their largest effects on communities, and most of them will be direct effects. After the initial stage of invasion, impacts are less predictable, and more likely to be caused by indirect effects through changes in the ecosystem.