General overview of zebra and quagga mussels: What we do and do not know

The zebra mussel, Dreissena polymorpha, and quagga mussel, Dreissena rostriformis bugensis, are both important invaders in freshwaters of the Northern Hemisphere. These two invaders have similar life habits and life-history characteristics but differ in timing and rates of spread, habitat requirements, growth, and population dynamics. While the zebra mussel is among the best-studied freshwater invertebrates, we do not always have comparable information for the quagga mussel, which limits our ability to predict the spread and ecological impacts of this important freshwater invader. Here we contrast what is known and not known about zebra and quagga mussels and highlight information that is needed, especially for the quagga mussel, if we are to accurately predict its population dynamics and future spread.