The Eurasian Zebra Mussel Dreissena polymorpha is apparently native to brackish and fresh waters of the northern regions of the Ponto-Caspian (Black, Caspian, Azov, and Aral) Sea drainages and brackish and freshwater tectonic lakes south of the Ponto-Caspian Seas (May et al. 2006 and references therein). As early as the 18th century, this mussel began to expand its range in Europe via canals constructed to connect European river basins and the 19th century linkage of the Ponto-Caspian Seas with the Baltic and North Seas resulted in shipping traffic that accelerated the spread of D. polymorpha throughout European waters. (Bij de Vaate et al. 2002; May et al. 2006 and references therein). Dreissena polymorpha was first detected in North America in the mid-1980s and spread rapidly. (A few years later, a related and similar exotic mussel, the Quagga Mussel [D. rostriformis bugensis], was detected in North America and within a couple of decades largely replaced the D. polymorpha in the Great Lakes of eastern North America.) (Brown et al. 2010)
The invasion of North America by D. polymorpha has resulted in enormous economic impacts and ecological disturbances. Connelly et al. (2007) studied the economic impact of D. polymorpha on surface water-dependent drinking water treatment and electric power generation facilities (where previous research indicated the greatest impacts). They estimated the cumulative cost to these facilities in North America between 1989 and 2004 to be several hundred million dollars.
Population studies of mitochondrial DNA indicate that invasive D. polymorpha populations in both North America and Europe originated from the Ponto-Caspian Sea region. This region is the source of many aquatic species that have invaded Western Europe and the North American Great Lakes. (Ricciardi and MacIsaac 2000; Bij et al. 2002; May et al. 2006).
As is the case for some other invasive filter-feeding bivalve mollusks, populations of D. polymorpha are often enormous, dominating the non-photosynthesizing biomass and clearing large volumes of water as they consume phytoplankton and extract calcium from the water to build their shells. A conspicuous result is the dramatic reduction of the pelagic part of the food web and a corresponding flourishing of the littoral part. (Strayer 2009, 2010) However, in at least one local region (the freshwater portion of the Hudson River estuary in the notheastern United States), there is evidence that the impacts of D. polymorpha on the local ecosystem have been greatly moderated during the two decades subsequent to the arrival of these mussels. Although this change is clear, the reasons for it are not. Blue crabs (Callinectes sapidus) currently appear to be important predators of D. polymorpha in the Hudson River and mortality from both Blue Crabs and other causes is much higher than it was early in the mussel invasion, but there is no evidence that populations of crabs or other predators in the Hudson have increased (Strayer 2011).
An important ecological impact of invading D. polymorpha in North America has been the decline and local extinction of native mussel species (e.g., Martel et al. 2001). Similar concerns exist for Europe, although preliminary work has suggested that the impact on the native mussel fauna in Europe may be less severe (Sousa et al. 2011).
Strayer (2009) provides an overview of what was learned about D. polymorpha in the two decades after its establishment in North America--and what important questions remain unanswered--with respect to both biology and public policy.
