Dreissena bugensis (mollusc)

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General Impact Nutrient loading and species introductions are thought to be two of the major environmental problems currently facing freshwater ecosystems (Richter et al. 1997, Hall et al. 2003 in Haynes et al. 2005), and both of these anthropogenic factors are of concern in the Great Lakes, USA (Haynes et al. 2005). Reduction in Native Biodiversity: D. bugensis causes changes in the structural characteristics of zooplankton including total abundance, biomass and species composition. Specifically, there is an inverse relationship between zooplankton abundance/biomass and density of Dreissena mussels (Grigorovich & Shevtsova, 1995). Dreissena infestations have caused upwards of 95% reduction in unionid numbers and extirpated eight species of unionids in some areas of the Great Lakes (Schloesser et al. 1998; Schloesser & Masteller 1999). Individuals attach themselves to the shells of other mussels, forming encrusting mats many shells thick (10-30mm). Modification of Natural Benthic Communities: Dreissena negatively affects benthic invertebrate communities, especially filter-feeding or deep-dwelling invertebrates that rely on detrital rain (Dermott and Munawar 1993, Strayer et al. 1998, Johannsson et al. 2000, in Haynes et al. 2005). Predicting benthic invertebrate community response to a change in nutrient levels is very difficult, and the potential synergistic effects of nutrient alterations and exotics such as Dreissena are complex (Haynes et al. 2005). Economic: Thick encrustations of mussels form on man-made structures or within raw water systems, impacting on operation and efficiency. D. bugensis can have major detrimental impacts on recreational and commercial shipping/boating as well as on water-using industries, potable water treatment plants and electric power stations (Ussery & McMahon, 1995).          Location Specific Impacts: Presque Isle Bay (North America)   Reduction in native biodiversity: In Presque Isle Bay on Lake Erie, dreissenid mussels surveyed sites experienced 100% unionid mortality after it was discovered that the invasive mussels were present. It is believed there are natural refugia areas that the mussels will be unable to invade but the impacts are still severe (Schloesser & Masteller 1999). Lake Erie (North America)   Competition: Driessena bugensis competes with and displaces native bivalves in Lake Erie (Bially & MacIsaac, 2000). Reduction in native biodiversity: In Lake Erie's eastern basin, dense colonies of Dreissena bugensis have infested profundal areas up to depths of 55m (Roe and MacIsaac 1997). Although some meiofaunal species have benefited from the presence of D. bugensis in the profundal zone, burrowing amphipod Diporeia hoyi numbers have declined sharply (Dermott and Kerec 1997; Mills et al 1999). Lake Michigan (North America)   Interaction with other invasive species: Dreissena bugensis has a potential role in expanding the depth range of Echinogammarus ischnus (Nalepa et al 2001). Modification of natural benthic communities: With the loss of Diporeia and increase in D. bugensis, the benthic community has become a major energy sink rather that a pathway to upper trophic levels. With this replacement of dominant taxa, we estimate that the relative benthic energy pool increased from 17 to 109 kcal m2 between 1994 /1995 and 2005, and to 342 kcal m2 by 2007. It is projected that previously observed impacts on fish populations will continue and become more pronounced as the D. bugensis population continues to expand in deeper waters (Nalepa et al, 2009). Modification of nutrient regime: Dreissena bugensis will likely cause other changes to the off- shore food web (Nalepa et al 2001). With D. bugensis now present and poised to expand in the offshore region, the rate of decline in Diporeia will likely increase, and the lake area devoid of this important fish-food organism will become more extensive (Nalepa et al 2001). Reduction in native biodiversity: Dreissena bugensis populations gowing in Lake Michigan which are replacing D. polymorpha in locations also contribute to the reduction of native amphipod Diporeia spp. (Nalepa et al, 2009). Lake Ontario (North America)   Modification of natural benthic communities: The establishment of Dreissena bugensis and D. polymorpha coincided with a drastic decline of native amphipod Diporeia spp. (Owens & Dittman, 2003). Reduction in native biodiversity: In response to the disappearance of Diporeia spp., believed to have resulted from the introduction of Dreissena bugensis and D. polymorpha, populations of two native benthivores, slimy sculpin and lake whitefish, collapsed in eastern Lake Ontario, perhaps due in part to starvation, because Diporeia was their principal prey (Owens & Dittman, 2003). St. Lawrence River (North America)   Fouling: Locations of St. Lawerence River where Dreissena bugensis occurred in densities of 4,000-20,000/m2 resulted in 90-100% native unionid mortality. D. bugensis colonize unionids bivalves in high densities. Data suggests that once Dreissena mass is equal to or exceeds that of the bivalve, it will be extirpated (Ricciardi et al, 1996). Russian Federation   Ecosystem change: Its ecological impact is unknown. Kakhovka Canal (Ukraine)   Modification of nutrient regime: Results of investigations concluded that structural characteristics of zooplankton including total abundance, biomass and species composition are lower in the areas supporting massive populations of Dreissena in the Main Kakhovka Canal. There is an inverse relationship between zooplankton abundance and biomass and density of Dreissena mussels, which exert pressure on zooplankton (Grigorovich and Shevtsova, 1995). Detroit River (United States (USA))   Reduction in native biodiversity: The present study documents extensive and severe mortality of unionids caused by dreissenid mussel infestations in the Detroit River of the Great Lakes. Infestation caused a 95% reduction in the number and extirpated eight species of unionids between 1986 (when zebra mussels were first introduced into the system) and 1992/1994. This study, and others, suggest that: (1) high mortality of unionids can occur between 4 and 6 yr after initial invasion by dreissenids or up to 8 yr depending on water current patterns; (2) species in the subfamilies Anodontinae and Lampsilinae were more vulnerable to infestation than species of Ambleminae; (3) numbers of individuals of commonly found species declined more than numbers of individuals of uncommonnly found species; and (4) numbers of uncommonly found taxa declined more than numbers of commonly found taxa (Schloesser et al 1998). Michigan (United States (USA))   Reduction in native biodiversity: A sampling of the Detroit River in 1982-1983 before the introduction of Dreissena bugensis and Dreissena polymorpha resulted in 97% live unionids of 20 different species, whereas a sampling in 1992 after the introduction of the two Dreissena spp. resulted in only 10% live unionids of only 13 different species. Surveys of native freshwater mussels along main channels of the Detroit River from 1992-1994 showed that unionids had been extirpated from all but four sites in the upper reaches of the river due to impacts of dreissenid mussels (Schloesser et al, 1998; Schloesser et al, 2006). Mississippi River (United States (USA))   Fouling: Diversity and densities of native mussels in decline (Ricciardi et al, 1996, Schloesser et al. 1996). Missouri River (United States (USA))   Fouling: Diversity and densities of native mussels in decline (Ricciardi et al, 1996, Schloesser et al. 1996).