Zebra mussels were first discovered in North America in 1988 in the Great Lakes. The first account of an established population came from Canadian waters of Lake St. Clair, a water body connecting Lake Huron and Lake Erie. By 1990, zebra mussels had been found in all the Great Lakes.

From the Great Lakes, zebra mussels have spread across the continental U.S. In 1991, zebra mussels escaped the Great Lakes basin and found their way into the Illinois and Hudson rivers. The Illinois River was the key to their introduction into the Mississippi River drainage which covers over 1.2 million square miles. In January 2008, zebra mussels were discovered in San Justo Reservoir in central California (D. Norton, pers. comm.). A population in Lake Texoma on the border of Texas and Oklahoma was confirmed in June 2009 (B. Hysmith, pers. comm.). A lake in western Massachusetts became infested in July, 2009 (T. Flannery, pers. comm.). 

After the eggs are fertilized, the larvae (veligers) emerge within 3 to 5 days and are free-swimming for up to a month. Optimal temperature for larval development is 20–22°C. Dispersal of larvae is normally passive by being carried with water currents. The dispersion of zebra mussels within a lake is controlled by physical conditions including wind strength, lake/shore morphometry, and current patterns (Stanczykowska and Lewandowski 1993). These conditions affect both spatial patterns of pelagic veliger density and benthic adult dispersion. Once the veliger undergoes morphological changes including development of the siphon, foot, organ systems and blood, it is known as a postveliger. Further subdivision of the larval stage has been delineated: (veliger) preshell, straight-hinged, umbonal, (postveliger) pediveliger, plantigrade, and (juvenile) settling stage (ZMIS 1996). The settling stage attaches to a substrate via protienaceous threads secreted from the byssal gland. The vast majority of veliger mortality (99%) occurs at this stage due to settlement onto unsuitable substrates. Sensitivity to changes in temperature and oxygen are also greatest at this stage. The larvae begin their juvenile stage by settling to the bottom where they crawl about on the bottom by means of a foot, searching for suitable substrate. They then attach themselves to it by means of byssal threads. Although the juveniles prefer a hard or rocky substrate, they have been known to attach to vegetation. As adults, mussels have a difficult time staying attached when water velocities exceed two meters per second.

Zebra mussels attach to any stable substrate in the water column or benthos, including rock, macrophytes, artificial surfaces (cement, steel, rope, etc.), crayfish, unionid clams, and each other, forming dense colonies called druses. Long-term stability of substrate affects population density and age distributions on those substrates. Within Polish lakes, perennial plants maintained larger populations than did annuals (Stanczykowska and Lewandowski 1993). Populations on plants also were dominated by mussels less than a year old, as compared with benthic populations. These populations of small individuals allow higher densities on plants. In areas where hard substrates are lacking, such as a mud or sand, zebra mussels cluster on any hard surface available. Given a choice of hard substrates, mussels prefer dark, rough substrates that are above the bottom of the lake bed (Kobak 2013). They also respond to the presence of predators by using byssal threads to attach more strongly to the substrate, forming aggregations, and reducing their upward movement (Kobak 2013). Research on Danish lakes shows factors that cause substrate to be unsuitable for both initial and long term colonization, including extensive siltation, some sessile benthic macroinvertebrates, macroalgae, and fluctuating water levels exposing mussels to desiccation (Smit et al. 1993). Population density of benthic adults has been observed to vary as widely as two orders of magnitude (e.g., <100 to >1500 individuals/m2) within individual Polish lakes due to these physical conditions. Tolerance limits of physical and chemical parameters are well known (Sprung 1993, Vinogradov et al. 1993, McMahon 1996).

Discrepancy exists when comparing temperature tolerance limits of North American and European populations, potentially due to the American population being founded by mussels from the southern limit of the European population's range. Most work in Europe has been done in the northern range. North American populations are generally adapted to warmer temperature regimes than their European counterparts. Although shell growth has been reported to occur at temperatures as low as 3°C, Lake St. Clair populations and some European populations display shell growth at 6–8°C. The optimal temperature range for adults extends to 20–25°C, but D. polymorpha can persist in temperatures up to 30°C. Short term tolerance of temperatures up to 35°C is possible if the mussels were previously acclimated to high temperatures. Rapid warming of shallow lakes has been hypothesized to detrimentally affect reproductive rates in Danish populations (Smit et al. 1993).

Oxygen demands are similar to those of other freshwater bivalves including unionids. Tolerance of "anaerobic" conditions has been reported for short time periods under certain temperatures and sizes, but zebra mussels cannot persist in hypoxic conditions. The lower limit of pO2 tolerance is 32–40 Torr at 25°C. Zebra mussels have been found in the hypolimnetic zone of lakes with oxygen levels of 0.1-11.2 mg/l, and in the epilimnetic zone with oxygen levels of 4.2–13.3 mg/l. Zebra mussels are described as poor O2 regulators, possibly explaining their low success rate in colonizing eutrophic lakes and the hypolimnion. Indeed, the distribution of Dreissenid mussels is severely limited in the central basin of Lake Erie, which routinely experiences bottom hypoxia (Karatayev et al. 2017). 

The salinity tolerance of zebra mussels is low.  Although some populations of European zebra mussels can be found in estuaries, their persistence has been speculatively attributed to reduced tidal fluctuation. Upper limits of freshwater bivalve salinity tolerance reach 8–10 ‰, and populations of European zebra mussels have been found to tolerate and range of salinities, from 0.6 ‰ (Rhine River) to 10.2 ‰ (Caspian Sea). North American populations generally tolerate salinity up to 4 ‰. Calcium and pH levels also influence survival and growth. In European populations, calcium concentrations of 24 mg Ca2+/l allow only 10% larval survival due to inhibition of shell development. Optimal calcium concentrations ranges from 40–55 mg Ca2+/l, but North American populations have been found in lakes with lower concentrations. North American populations require 10 mg Ca2+/l to initiate shell growth and 25 mg Ca2+/l to maintain shell growth. Larval development is inhibited at pH of 7.4. Higher rates of adult survival occur at a pH of 7.0–7.5, but populations have been found in the hypolimnetic zone of lakes with a pH of 6.6–8.0, and in the epilimnetic zone with a pH of 7.7–8.5. Optimal larval survival occurs at a pH of 8.4, and optimal adult growth occurs at pH 7.4–8.0.

The life span of D. polymorpha ranges between 3–9 years. Maximum growth rates can reach 0.5 mm/day and 1.5–2.0 cm/year. Adults are sexually mature at 8–9 mm in shell length (i.e. within one year in favorable growing conditions).

Zebra mussels are filter feeders having both inhalant and exhalant siphons. They are capable of filtering about one liter of water per day while feeding primarily on algae. Zebra mussels are able to filter particles smaller than 1 µm in diameter, although they preferentially select larger particles (Sprung and Rose 1988). At a 90% efficiency rate, zebra mussels are much more efficient at filtering such small particles than are unionids and Asiatic clams (Noordhuis et al. 1992).  Bacteria, which D. polymorpha also tends to filter more effectively than native unionids, may represent another important food source (Cotner et al. 1995, Silverman et al. 1996, Silverman et al. 1997). Microzooplankton (e.g., rotifers and veligers) are ingested by zebra mussels, but larger zooplankton are not eaten (MacIsaac et al. 1991, MacIsaac et al. 1995). Veligers also filter material, but their impact is far less than that of sessile adults. Settled mussels exerted 103 times the grazing rate of veligers in western Lake Erie, for example (MacIsaac et al. 1992).

Filtration rate is highly variable, depending on temperature, concentration of suspended matter, phytoplankton abundance, and mussel size (reviewed by Noordhuis et al. 1992).  Zebra mussels can adjust their filtration rates (more frequent interruption of filtering or slower pumping rates) and/or produce pseudofeces above an incipient limiting concentration (ILC) of algae to maintain a constant consumption rate (Fanslow et al. 1995, MacMahon 1996, Sprung and Rose 1988). Feeding activity can be described by the clearance rate (percentage of algal biomass removed from the water column over time), biomass of cleared algae (BCA), feces production and pseudofeces production (µg F or P/BCA). For example, Berg et al. (1996) examined the effects of zebra mussel size and algae species and concentration on zebra mussel feeding activity. Clearance rates were constant over varying concentrations of pure cultures of Chlamydomonas reinhardtii, a spherical unicellular species 7.42 µm (± 0.13 µm) in diameter. This indicates that the concentrations used in experiments were below the ILC. However, clearance rates decreased, with increasing concentrations of Pandorina morum, a species made up of colonies with varying numbers of cells that are individually as large as C. reinhardtii. This indicates that the concentrations used in experiments were above the ILC. Large zebra mussels (20-25 mm in length) displayed a higher clearance rate across all concentrations of C. reinhardtii than did small mussels (10-15 mm). Incipient limiting concentration differed in this study from previous studies conducted with European populations. Vanderploeg et al. (2017) found that seston quality and availability affects zebra mussel feeding rate and excretion levels. In Saginaw Bay, filtration rate increased with higher seston concentrations and water temperatures, but was not found to be related to seston composition (POC:TSS, chl:TSS) (Fanslow et al. 1995).  No diel patterns of filtration rate have been found. During spring, filtration rates rise dramatically as waters warm from 5–10°C, then level off with respect to temperature, and may be inhibited at temperatures over 20°C. Increased suspended matter can reduce filtration activity to a minimum required to maintain oxygen demand. A sigmoidal relationship exists with filtration rate and size, but this may be an effect of aging. Thus, zebra mussel size, phytoplankton species, and regional population differences will affect clearance rates, ILC, and feces/pseudofeces production.

Material filtered by zebra mussels is either ingested or expelled as feces or mucus-covered pseudofeces. True fecal pellets are chemically altered, larger, and denser. Zebra mussels produce pseudofeces to avoid ingesting non-food material. Pseudofeces production may also be a mechanism to deal with overabundance of food (e.g., algal concentrations above the ILC, incipient limiting concentration), and possibly as a way to reject unpalatable algae. Pseudofeces production increases with increasing suspended solid concentration, as well as increasing temperature, albeit to a much lesser extent (MacIsaac and Rocha 1995, Noordhuis et al. 1992).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic	Beneficial

Dreissena polymorpha has a high environmental impact in the Great Lakes.

Realized:
Zebra mussels can have profound effects on the ecosystems they invade. They primarily consume phytoplankton, but other suspended material is filtered from the water column including bacteria, protozoans, zebra mussel veligers, other microzooplankton, and silt. Large populations of zebra mussels in the Great Lakes and Hudson River reduced the biomass of phytoplankton significantly following invasion. Diatom abundance declined by 82–91%, and transparency as measured by Secchi depth increased by 100% during the first years of the invasion in Lake Erie (Holland 1993). As the invasion spread eastward during the years 1988 to 1990, successive sampling stations recorded declines in total algae abundance from 90% at the most western station to 62% at the most eastern (Nichols and Hopkins 1993). In Lake Huron’s Saginaw Bay, sampling stations with high zebra mussel populations experienced a 60–70% drop in chlorophyll a and doubling of Secchi depth (Fahnenstiel et al. 1993). Phytoplankton biomass declined 85% following mussel invasion in the Hudson River (Caraco et al. 1997). Increasing silica concentrations also suggest that decreasing phytoplankton populations are associated with dreissenid invasions. From 1983-2008, average spring silica concentrations in open water increased in Lake Michigan and  increased slightly in Lake Huron, while summer silica concentrations experienced significant increases in both lakes. Dramatic increases in summer silica were initiated in the early 2000s in Lake Huron and in 2004 in Lake Michigan, though these seem to be associated with the expansion of quagga mussel (D. bugensis) populations in the lakes at those times (Evans et al. 2011). These findings indicate that the utilization of silica via primary production has likely decreased, and that Lakes Huron and Michigan are undergoing gradual oligitrophication (Evans et al. 2011). However, the extent of change that zebra mussels can exert on the phytoplankton community’s species composition is unresolved.

Zebra mussels readily reject blue-green algae, such as Microcystis, as pseudofeces (Vanderploeg et al. 2001), perhaps identifying the cyanobacteria internally based on chemical cues (ten Winkel and Davids 1982).  The presence of this cyanobacterium does not inhibit filtering, except in mass abundances such as a bloom (Lavrentyev et al. 1995, Noordhuis et al. 1992). When invaded by zebra mussels, inland lakes with lower nutrient levels are more frequently dominated by Microcystis (Raikow et al. 2004, Sarnelle et al. 2010). A possible explanation was attained in controlled experiments, which indicated that excessive Microcystis growth could be related to a lower nitrogen:phosphorus ratio in environments with zebra mussels relative to those without (Bykova et al. 2006). Microcystis became a prevalent alga in Saginaw Bay, Lake Huron following the invasion of zebra mussels. The introduction appeared to spur a number of other changes to the phytoplankton community as well, including a shift from shade-tolerant species to light-tolerant species (Fishman et al. 2010). 

The zooplankton community has also been affected by the invasion of zebra mussels. Zooplankton abundance dropped 55–71% following mussel invasion in Lake Erie, with microzooplankton more heavily impacted (MacIsaac et al. 1995). Mean summer biomass of zooplankton decreased from 130 to 78 mg dry wt. m-3 between 1991 and 1992 in the inner portion of Saginaw Bay. The total biomass of zooplankton in the Hudson River declined 70% following mussel invasion, due both to a reduction in large zooplankton body size and a reduction in microzooplankton abundance. These effects can be attributed to reduction of available food (phytoplankton) and direct predation on microzooplankton. Increased competition in the zooplankton community for newly limited food, which could lead to a decline in individual zooplankter size, is predicted to result from zebra mussel infestation. Based on knowledge of their competitive abilities, hypotheses can also be formulated as to which species will prevail.

Zebra mussels can have a significant effect on nutrient cycling in invaded ecosystems. As stated in a hypothesis called the “nearshore phosphorus shunt,” zebra mussels can direct phosphorus and other nutrients to nearshore areas inhabited by mussels and retain them there, while offshore regions suffer from declining nutrient levels and often become mesotrophic or oligotrophic (Hecky et al. 2004). This is possible due to the ability of zebra mussels to filter a significant amount of the particles and nutrients that are entering the system (e.g., via a river or tributary), preventing the movement of nutrients to offshore areas. Production of feces and pseudofeces provide one mechanism by which usable phosphorous is then regenerated in the proximate benthos and water column, leading to increased primary productivity in the nearshore zone relative to the offshore pelagic zone (Hecky et al. 2004). This hypothesis could thus explain the sudden reemergence of Cladophora, a nuisance benthic algae, in the otherwise clear nearshore regions of Lake Ontario and Lake Erie following the invasion of zebra mussels (Auer et al. 2010, Hecky et al. 2004, Limburg et al. 2010). In further support of the hypothesis, Roditi et al. (1997) found that biodeposits of zebra mussels to be organically enriched, including 3.9% live algae by weight. Resuspension of this material occurred in their system, a tidal estuary, which may have mitigated the potential impacts of biodeposition to the benthos.

The filtering and excretion activity of zebra mussels can alter physical and chemical conditions.  For instance, zebra mussels have been found to remove metals from the water column of Lake Erie and deposited them to the bottom at high rates (Klerks et al. 1996). In Lake Erie, the rate of biosedimentation through pseudofeces production was very high (28 mg/cm2 day at a density of 1180 individuals/m2) under turbid conditions, lending support to the hypothesis that zebra mussels are responsible for increased water clarity observed since mussel introduction (Klerks et al. 1996).

A change in the feeding behavior of lake whitefish may be related to the nearshore shunt hypothesis (Rennie et al. 2009). A study of 5 year old lake whitefish in South Bay, Lake Huron discovered a diet with a greater reliance on nearshore prey in this species following zebra mussel invasions. Stomach content analysis was used along with the measurement of isotopic ratios in fish scales over time. Following zebra mussel invasion, an increase of 3‰ δ¹³C and a decrease of 1‰ δ¹⁵N from isotope levels that had remained stable for nearly 50 years were observed. The proposed explanation is a transition in diet to nearshore benthic organisms, including zebra mussels, which are now suspected to be a common food item of lake whitefish (Madenjian et al. 2010). The mean depth of capture for lake whitefish also shifted inshore, suggesting that the diet and habitat of lake whitefish may be changing due to the indirect effects of zebra mussels on nutrient cycling and resulting food availability in the nearshore zone relative to the profundal (Rennie et al. 2009). Furthermore, while dreissenids now appear to be a contributing food source to whitefish diet, this shift appears to be less energetically profitable to whitefish, whose growth rate has declined following dreissenid invasion despite sustained levels of consumption (Pothoven and Madenjian 2008).

Populations of Diporeia spp., a native amphipod which once dominated benthic habitats, have decreased dramatically since dreissenids were first introduced in the 1990s. Diporeia populations at 30–90 m depths declined by 96% in Lake Michigan between 1994/1995 and 2005 and by 99% in Lake Ontario between 1994 and 2003 (Nalepa et al. 2009, Watkins et al. 2007). These findings agree with a 13 yr annual benthic survey (1997-2009) initiated by the EPA, which also found significantly reduced populations of Diporeia in Lakes Huron, Michigan, and Ontario (Barbiero et al. 2011). These declines were coincident with the initial expansion of D. polymorpha, but have continued to increase following expansion of D. bugensis and its gradual replacement of D. polymorpha (Watkins et al. 2007, Nalepa et al. 2009). Diporeia population decline is potentially due to reductions in phytoplankton abundance (an important food source) or through the introduction of toxins and pathogens associated with dreissenids and their waste products (Cave and Strychar 2015, Fahnenstiel et al. 2010, McKenna et al. 2017, Nalepa et al. 2006, Watkins et al. 2007).  Diporeia is an important prey item linking the benthos to higher trophic levels, and it has been suggested that the shift from Diporeia to Dreissena has transformed the benthic community into an energy sink which may no longer support the upper food web (Nalepa et al. 2009).

Other effects include the extirpation of native unionid clams through epizootic colonization (Baker and Hornbach 1997, Schloesser et al. 1996). Zebra mussels restrict valve operation, cause shell deformity, smother siphons, compete for food, impair movement, and deposit metabolic waste onto unionid clams. Survival rates of native unionid mussels in the Mississippi River, Minnesota have been shown to decline significantly with an increase in zebra mussel colonization (Hart et al. 2001). Unionid mortality is correlated with zebra mussel fouling across a broad range of habitats; although other factors have contributed to unionid declines, zebra mussel colonization has increased the local extinction of unionid species by a factor of 10 (Ricciardi et al. 1998). To date, unionids have been extirpated from Lake St. Clair and the Detroit River, and in much of western Lake Erie and the upper St. Lawrence River (Ricciardi et al. 1996, Schloesser et al. 2006).

Potential:
Increased water clarity allows light to penetrate further, potentially promoting macrophyte populations (Scheffer et al. 1993, Skubinna et al. 1995). As macrophytes can be colonized by dreissenid veligers, the macrophyte community may be altered if such colonization proves detrimental. Increased light penetration may also cause water temperatures to rise and thermoclines to become deeper (Schindler et al. 1996). As phytoplankton are consumed, the dissolved organic carbon (DOC) concentration may drop. Indeed, inland lakes with zebra mussels have been found to have lower concentrations of DOC (Raikow 2002). Macrophytes could eventually compensate for this as they are also a source of DOC, but there may be a lag period between the time when phytoplankton biomass declines and macrophytes proliferate. This could produce a period of time when UVB light penetrates deeper into the water column, because DOC absorbs UVB radiation. Zebra mussels have also recently been shown to be able to directly assimilate DOC (Roditi et al. 2000).

The fate of pseudofeces once it is expelled is not well understood. It has been speculated that benthic deposition of feces and pseudofeces may aid bacterial productivity, thus producing a source culture that zebra mussels can feed upon (Silverman et al. 1996). Increasing amounts of biodeposits could have an impact on multiple trophic levels via changes to the physical environment. A current study in Brocton Shoal, Lake Erie, suggests that colonization of lakebed areas by dreissenid mussels and the consequent filling of remaining interstitial spaces with pseudofeces and fine-grained sediments may significantly eliminate valuable native habitat (S. Mackey, pers. comm.). Brocton Shoal, once thought to be an important area for lake trout spawning, appears to have diminished suitability as a spawning ground, potentially due to such impacts (S. Mackey, pers. comm.).  It has also been proposed that biodeposition of feces and pseudofeces might cause observed increases in benthic macroinvertebrate populations (Stewart and Haynes 1994).

The fate of live algae bound into pseudofeces is not well known. Bastviken et al. (1998) speculate that phytoplankton which survives the pseudofeces process must be resuspended in order to survive, a process less likely to occur in inland lakes than in tidal estuaries.  If survivorship following filtration is not equal among phytoplankton species, then this mechanism could alter community species composition.  

Effects may continue through the food web to fish. Reductions in zooplankton biomass may cause increased competition, decreased survival, and decreased biomass of planktivorous fish. Alternatively, as microzooplankton are more heavily impacted by zebra mussels, larval fish population may be more acutely affected than later life stages. This may be especially important in inland lakes with populations of pelagic larval fish such as bluegills. Benthic feeding fish may benefit in contrast to planktivorous fish, or behavioral shifts from pelagic to benthic-feeding may occur. In addition, proliferation of macrophytes may alter fish habitat and thus, the fish community. Experimental evidence exists that zebra mussels can reduce the growth rate of larval fish through food web interactions (Raikow 2004). Conclusive negative impacts on natural populations of fish, however, have yet to be observed (see Bunnell et al. 2009 and 2014, Raikow 2004).

Biomagnification of toxic contaminants through the food web is another concern of zebra mussel invasion, especially because mussel predation by round goby Neogobius melanostomus has provided a link between Dreissena and higher trophic levels (Hanari et al. 2004, Jude et al. 2010). Biomagnification of polychlorinated biphenyls (PCBs) was observed in Gammarus amphipods associated with zebra mussels, indicating concentration of pollutants in zebra mussel feces or pseudofeces can transfer to other trophic levels (Bruner et al. 1994). Many species of birds known to be predators of zebra mussels occur in the Great Lakes region. While a new food source may benefit such predators, biomagnification of toxins into both fish and birds is possible. Tillit et al. (2009) documented levels of thiaminase activitiy in zebra mussels ranging from 10,600-47,900 pmol • g-1 • min-1 in Lakes Michigan, Huron, and Ontario. This is 5–100 times more thiaminase activity than is found in most Great Lakes fish. Increased thiaminase activities can diminish and deplete thiamine levels necessary for fish health and have been known to cause early mortality syndrome (EMS) in some species (Fitzsimons et al. 1999).

Like other mollusks, D. polymorpha is capable of hosting a variety of parasites, although the parasite load varies across its introduced range and appears to be lower in North America (Mastitsky et al. 2010). In particular, D. polymorpha acts as an intermediate host of the trematode Bucephalus polymorphus, which has caused pathologies and mortalities in cyprinids across parts of Europe (Molloy et al. 1997). Such effects do not result from all infections of D. polymorpha by B. polymorphus, suggesting that other factors may be involved (Molloy et al. 1997).

Dreissena polymorpha has a high socio-economic impact in the Great Lakes.

Realized:
Zebra mussels are notorious for their biofouling capabilities—colonization of water supply pipes of hydroelectric and nuclear power plants, public water supply plants, and industrial facilities. When inhabiting pipes, they tend to constrict water flow, thereby reducing the intake in heat exchangers, condensers, fire-fighting equipment, and air conditioning and cooling systems. Zebra mussel densities have been as high as 700,000/m² at one power plant in Michigan and have reduced water treatment pipe diameters by as much as two-thirds (Griffiths et al. 1991). Continued attachment of zebra mussel can cause corrosion of steel and concrete, affecting its structural integrity.

Navigational and recreational boating can be affected by increased drag from attached mussels. Small mussels can get into engine cooling systems causing overheating and damage. Navigational buoys have been sunk under the weight of attached zebra mussels. Fishing gear can be fouled if left in the water for long periods. Deterioration of dock pilings has increased when they are encrusted with zebra mussels.

Direct economic costs have resulted from the invasion of zebra mussels in the form of maintenance and repair of power plants, industrial facilities, and other businesses, as well as research, monitoring, and control. A wide variety of estimations have been made regarding zebra mussel-related expenses, ranging from $92,000 per hydroelectric plant per year to $6.5 billion in total costs over 10 years (Lovell et al. 2006).

High levels of potentially toxic cyanobacteria (Microcystis in particular) have been documented in otherwise low-nutrient lakes invaded by zebra mussels (Sarnelle et al. 2010, Vanderploeg et al. 2001), sometimes proliferating in years just following zebra mussel invasion (Fishman et al. 2010). A similar correlation has been documented with the non-toxic nuisance green algae Cladophora. The reemergence of this species in Lake Ontario, Lake Erie, and Lake Michigan following the establishment of zebra mussels has been largely attributed to the resulting changes in nutrient cycling and water clarity (Auer et al. 2010, Hecky et al. 2004). Cladophora has received considerable negative attention from the public (Auer et al. 2010). Residents and business owners on Lake Ontario have attributed decreases in revenue or property values to beach fouling and excessive blooms following zebra mussel invasion (Limburg et al. 2010).

Potential:
Although there is little information on zebra mussels affecting irrigation equipment, farms and golf courses could be likely candidates for infestations.

Moreover, reductions in zooplankton biomass may cause increased competition, decreased survival, and decreased biomass of planktivorous fish, including commercially important species.

There is little or no evidence to support that Dreissena polymorpha has significant beneficial effects in the Great Lakes.

Realized:
Several species of native fish may prey on zebra mussels in varying degrees, including lake whitefish (Madenjian et al. 2010, Rennie et al. 2009), freshwater drum, pumpkinseed, yellow perch, and rock bass among others (Watzin et al. 2008), although the extent of benefit to these species relative to pre-invasion is unknown.

Increased water clarity following zebra mussel introduction is perceived as a benefit by some, especially business owners and residents on invaded water bodies (Limburg et al. 2010).

Potential:
Experimental studies have shown that zebra mussels generally increase benthic macroinvertebrate densities, sometimes by more than 10-fold (Botts et al. 1996, Ricciardi et al. 1997, Ward and Ricciardi 2007).  Some benthic fishes may benefit from the increased food resource.

Certain benefits of the zebra mussel invasion in Europe have been noted, including its role as a food source for fish and native waterfowl populations, some populations of which increased following zebra mussel introduction. Zebra mussels have also been used in biomonitoring of contaminants (Mackie et al. 1989).

Federal law (Lacey Act 1990) prohibits the possession and transportation of zebra mussels in the United States unless intended for research.

The following regulations apply to all vessels equipped with ballast water tanks that enter a United States port on the Great Lakes after operating in waters beyond the exclusive economic zone. Vessels are required to exchange ballast water beyond the exclusive zone prior to entering any Great Lakes port. Ballast exchange may also be conducted in waters that are considered a non-threat to the infestation of an aquatic nuisance species in the Great Lakes (Allowable waters stated under ANS Task Force section 1102(a)(1)). Vessels are also required to use environmentally sound ballast water management methods if deemed necessary (NANPCA 2000).

In New York, it is unlawful to intentionally release zebra mussels into state waters (N.Y. Envtl. Conserv. Law § 11-0507). In Pennsylvania, it is unlawful to possess, introduce, import, transport, sell, purchase, offer for sale, or barter zebra mussels (58 Pa. Code § 63.46, 58 Pa. Code §§ 71.6 and 73.1). In Ohio, it is unlawful to possess, import, or sell zebra mussels (Ohio Admin. Code § 1501:31-19-01(K)(4)). In Indiana, it is unlawful to import, possess, or release zebra mussels into public or private waters (Ind. Admin. Code tit. 312, r. 9-9-3(d) and (e)). In Michigan, zebra mussels are a restricted species (Mich. Comp. Laws § 324.41301) and therefore cannot be possessed unless it is to identify, eradicate, or control the species (Mich. Comp. Laws § 324.41303). In Wisconsin, it is unlawful to transport, transfer, or introduce zebra mussels (Wis. Admin. Code § NR 40.05). In Minnesota, it is unlawful to place or attempt to place a watercraft, trailer, or plant harvesting equipment that has zebra mussels attached into state water (Minn. Stat. § 84D.10). Persons leaving the state are required to drain boats and related equipment during transportation on a public road (Minn. Stat. § 84D.10 and Minn. R. 6216.0500). (Kaminski Leduc 2011).  Illinois lists zebra mussels as injurious species (ILL. ADM. CODE CH. 1, § 805).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Given the widespread established of zebra mussels in the Great Lakes, total eradication is considered impossible with current technologies. Control measures have been tested in some Great Lakes nearshore environments, but at small scales and with the main goal to begin exploring feasibility.  Control efforts focus primarily on protection of human infrastructure (such as water intakes) and along vectors of spread (such as boats, trailers, gear, etc).  Controlling zebra mussels to minimize effect on natural and anthropologic systems is expensive, regardless of the method(s) chosen. Microencapsulated “biobullets” are being developed in the UK as a more efficient method to deliver control agents to mussels (Costa et al. 2011), but these are not yet tested for open water application or approved by the EPA.

Biological
Biological control so far has proven to be ineffective in controlling Dreissena species.  Predation by migrating diving ducks, fish species, and crayfish may reduce mussel abundance, though the effects are short-lived (Bially and MacIsaac 2000). Invasive round goby, when abundant, are effective at suppressing dreissenid mussels (Lederer et al. 2008) but it should not be introduced as a biocontrol agent.  Other biological controls being researched are selectively toxic microbes and parasites that may play a role in management of Dreissena populations (Molloy 1998). Laboratory testing shows strain CL145A of Pseudomonas fluorescens (a bacterium) to be highly lethal to zebra mussels; capable of eliminating over 90% of adults and 100% of larvae (Abdel-Fattah 2011, Molloy 2002). Commercially, this product is known as Zequanox® and is developed by Marrone Bio Innovations (Abdel-Fattah 2011). Open water Zequanox® studies have been conducted on zebra mussels in Minnesota (Lund et al. 2018), Illinois (Whitledge et al. 2015), and Ireland (Meehan et al. 2014).

Interfering with the synchronization of spawning by adults in their release of gametes could also offer control of Dreissena populations (Snyder et al. 1997). Another approach would be to inhibit the planktonic veliger (larvae) from settling and attaching to a surface to begin development (Kennedy 2002).

Physical
Effective physical controls of Dreissena include drawing down water from public sources or a groundwater well, using infiltration intakes or sandfilter intakes (filter out veligers), thermal treatments, carbon dioxide pellet blasting, high-pressure water jet cleaning, mechanical cleaning, freezing, scraping, scrubbing, pigging, and desiccation. Potential controls include the use of benthic mats, electrical fields, pulse acoustics, low-frequency electromagnetism, ultraviolet light (UV light), and reduced pressure (USACE 2002).

Physical removal of visible vegetation (which may harbor small mussels) from boats, trailers and other equipment being moved from one water body to another is an important method in controlling the spread of zebra mussels.  Flushing engines, cooling systems, live wells and bilge with water over 110^oF will kill veligers and 140^oF will kill adults.  Air drying equipment for 5 days will kill most larvae and smaller mussels, but large mussels may survive two weeks out of water.

Placement of water intakes (in areas too deep or otherwise unsuitable for zebra mussel colonization) has been used as a form of physical control, but this is less successful in areas which also have quagga mussels.

Chemical
Oxidizing chemical control treatments effective against D. polymorpha include hypochlorite reaction, chloramine, chlorine dioxide, bromine, ozone, potassium, permanganate, and sodium chlorite. Non-oxidizing chemicals include copper, niclosamide, and potassium ions. However, application of these chemicals can be detrimental to ecosystem and/or human health so possible effects should be thoroughly evaluated before use (Boelman et al. 1996, Sprecher and Getsinger 2000).

Various chemical coatings – including copper-based, tributyltin-based, copolymer, vinyl/epoxy, resin and other films -  can be applied to structures to prevent the attachment of zebra mussels.   Tributyltin-based antifoulants are extremely toxic and restricted by federal law (OH Sea Grant 1992). 

Other

Other potential methods of zebra mussel control include oxygen deprivation, radiation, and electric currents.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

For more information on Zebra mussel control in the Great Lakes region, please visit the Invasive Mussel Collaborative and the Collaborative's Dreissena Project Coordination Mapper.

The initial invasive range of zebra mussels in the Great Lakes has decreased due to displacement by the congeneric quagga mussel.  There are multiple mechanisms by which quagga mussels displace zebra mussels, including differences in growth, reproduction, respiration, movement, and development (Ram et al. 2012; Karateyev et al. 2015; D'Hont et al. 2021).  Zebra mussels still dominate in inland lakes and rivers and the two species coexist in shallow, productive systems such as Green Bay in Lake Michigan, Saginaw Bay in Lake Huron, and Western Lake Erie.

Growth rate for zebra mussels in Texas lakes have been among the fastest recorded in North American and Europe, at 127.9 μm day^-1 (Locklin et al. 2020).