Ecological and Economic Effects of Invasive Mussels
Quagga and zebra mussels (Dreissena spp.) are known as ecosystem engineers because they control the availability of resources to other organisms by the physical changes they cause in the environment (Jones et al. 1994) and have profound effects on lake and river ecosystem function and structure (Zhu et al. 2006). The ecological effects of these mussels are considered the most far-reaching relative to other aquatic invasive species (AIS), causing local extinction of many native mollusks (Strayer and Malcom 2007; Burlakova et al. 2014), changing the structure of food webs and fish assemblages, and contributing to the collapse of valuable sport fish populations (Kelly et al. 2010; Bossenbroek et al. 2009; Strayer 2009; Pimentel et al. 2005). Increased occurrences of harmful algal blooms (Higgins and Vander Zanden 2010) can contribute to declines in fish populations (Knoll et al. 2008). Once established, invasive mussels commonly reach densities in excess of 10,000 individuals per square meter (Depew 2021).
System-wide effects of quagga and zebra mussels depend on water mixing rates, lake morphology, and turnover rates (Karatayev et al. 2015). Quagga mussels can be found in all regions of a lake, form larger populations, may filter larger volumes of water and may have greater system-wide effects (especially in deep lakes) compared to zebra mussels, which are restricted to shallower portions of lakes (Karatayev et al. 2015). After initial invasion, invasive mussels will primarily have direct effects on ecological communities whereas post-invasion, less predictable impacts will likely be indirect effects that cause ecosystem changes (Karatayev et al. 2015). Proactive, pre-invasion management investments that emphasize the importance of strong prevention and early detection programs have been shown to be much lower than re-active, post-invasion expenditure (Cuthbert et al. 2022).
Quagga and zebra mussels filter particles from the water, resulting in improved water clarity (Karatayev et al. 1997, 2002), and corresponding increases in "benthification," (Mills et al. 2003). Scientists refer to this as "turning ecosystems upside down" because of the transfer of energy to littoral areas with concurrent increases in benthic biomass (Mayer et al. 2014; Rumzie et al. 2021).
Zebra mussels cost businesses and communities more than $5 billion in the first 10 years after invasion (Boelman et al. 1997). Because of the increase and extent of biological invasions through time, the total costs of these invasions have markedly increased between 1970 and 2017. Biological invasions show no sign of slowing down, highlighting the importance of evidence-based and cost-effective management actions (Daigne et al. 2021). A study conducted in Ontario, Canada revealed the majority of invasive species-related expenditures are borne at the municipality level (Vyn 2018).
Hydroelectric power plants and municipal water supply facilities
Clear Lake is a source of water for the Clear Lake Oaks County Water District, which treats and provides municipal drinking water for 4,700 people. In addition, many individual home owners with individual water systems, draw water from the lake. In 2022, health and tribal officials reported unprecedented levels of cyanotoxins in some areas of Clear Lake, which affects people using individual water systems.
Invasive mussels pose serious threats to water resources hydropower infrastructure and operations (Rumzie et al. 2021). Invasive mussels can affect all facility components exposed to raw water; mussels can clog pipelines and water intakes and disrupt operations at hydroelectric power plants, municipal water supply facilities, and conveyance systems used in irrigation, resulting in water lines incapable of supplying a consistent and reliable source of water (Vissichelli 2018). Smell, bacteria, and decay are other key issues associated with a mussel infestation; management response is continual cleaning, treatment, mitigation filters, and other actions. A 2021 study of 13 hydropower facilities in Canada and the United States (Rumzie et al. 2021) documented costs associated with established invasive mussels in both preventative control measures and increased maintenance.
Preventative control capitol costs (one-time costs) ranged from $100,000 to $200,000 per facility
Preventative control annual costs ranged from $4,000 to $141,700 per facility
Increased maintenance reoccurring costs ranged from $22,000 to $505,000 per facility
Increased maintenance annual costs ranged from $26,000 to $112,000 per facility
Annual monitoring costs ranged from $1,970 to $47,245 per facility
Unplanned outages cost per occurrence ranged from $44,000 to $80,000 per facility
Unplanned outages total cost was $849,000
Examples of preventative and maintenance costs include treating with chlorine, cleaning generator coolers 3-4 times per year to remove mussel debris, and increased labor costs to maintain all hydropower equipment.
The cost to remove mussels and manage drinking water intakes at Hoover, Davis, and Parker Dams, three facilities with invasive mussel infestations on the Colorado River, was more than $6,026,100 in 2016. Mussel-related costs at Hoover, Davis, and Parker Dams through 2016 totaled $6,025,100, and expected costs from 2017 to 2026 totaled $10,372,108 (Boyd 2016). The State of Washington estimated direct impacts to dams from invasive mussels is $42.9 million (Community Attributes 2017). The cost for the management response is passed to the consumer (Vissichelli 2018).
Recreational boating and public use
Lake County relies on more than $1 million annually from resident and non-resident fishing licenses. In locations outside of Lake County where mussel infestations occur, boaters face increased costs from mussels growing on hulls, engines, and steering components. Beaches can become unusable due to the sharp shells and pungent odors of dead mussels washing ashore. Detrimental ecological changes and changes in some fish species, have occurred in lakes where invasive mussels have become established (Nelson et al. 2022). The potential exists for disastrous collapse of native fish populations in water bodies in which invasive mussels become established (Nelson et al. 2022).
The estimated cost to remove mussels from boat launch infrastructure is $170,000 ($750/boat launch) (Community Attributes 2017). Estimates of additional boat maintenance expenses resulting from AIS in Lake Tahoe ranged from $200 to $400 per year per boat (USACE 2009). A 2% to 10% reduction in recreational fishing revenue (residents only) as a result of an invasion of mussels would cost Montana between $3.8 and $19.3 million annually (Nelson 2019). The potential effects to fisheries, hatcheries, and spawning runs as a result of mussels becoming established is significant (Rumzie et al. 2021). Examples include a $19 million/year reduction in sport fishing revenues in Michigan's Lake Huron (Michigan DNR 2019) to an estimated hundreds of millions of dollars annually to the Columbia River Basin or Snake River (IEAB 2013).
Montana estimated the top three stakeholder groups facing the largest potential economic impacts from dreissenid mussel invasion were tourism, hydropower, and irrigation accounting for 60 to 75 percent of the total potential damages statewide (Nelson 2019). In Montana, the estimated 2% to 10% potential annual loss in revenue from reduced tourism as a result of invasive mussel introductions equates to $17.8 million to $89 million (Nelson 2019).
Most of the invasive mussel-induced alterations to a lake ecosystem are detrimental to lake aesthetics, which can affect nearby property values (TRPA 2014, DeBruyckere 2019, Nelson 2019). The estimated 5.8% to 10% potential reduction to privately owned lakefront property values as a result of a mussel invasion equates to $288 million to $497 million, with an additional corresponding potential annual loss in property tax revenue (5.8% to 10%) of $2.2 to $3.8 million annually (Nelson 2019). Expanded invasive aquatic plant coverage reduced property values in King County, Washington lakefront homes by 19% (Olden and Tamayo 2014), and in Vermont, property values were reduced by 1% to 16% (Zhang and Boyle 2010).
Top photo: A water delivery pipe encrusted with invasive mussels. Photo to the right. Lake Natoma dam in Northern California. An introduction of invasive mussels to this lake could significantly increase operational costs.
Top left: Lake Sonoma marina. Bottom left: Outboard motor encrusted with invasive mussels. Right: Person walking along lake shoreline infested with invasive mussel. Mussel photo credits: www.westernais.smugmug.com.
Properties along the shoreline of Clear Lake could experience declines in property value if invasive mussels become established in the lake. Trickle-down effects to the county would likely occur, with reductions in annual property tax revenue.