Shell length-frequencies were determined for samples of Dreissena rostriformis bugensis collected <2 m depth from Las Vegas Boat Harbor (LVBH), Callville Bay Marina (two samples, CBM-1 and CBM-2), and Lake Mead Marina (LMM) in the Boulder Basin of Lake Mead and Katherine Landing Marina (KLM) in the lower end of Lake Mohave within two months of initial discovery of D. rostriformis bugensis in Lake Mead at LVBH on 06/01/2007. Two annual shell length (SL) cohorts were present at all four sites consisting of individuals presumed to have settled during spring-fall of 2005 and 2006, respectively. Members of the most recently settled 2006 cohort numerically dominated all samples; relative ratios of individuals in the LVBH, CBM-2, LMM, and KLM 2006 versus 2005 cohorts being 174:1, 95:1, 172:1 and 65:1, respectively. Mean shell lengths of the LVBH, CBM-1, CBM-2, KLM and LMM 2006 cohorts were 6.86 (s.e. = ±0.126), 9.59 (±0.080), 9.31 (±0.194), 10.49 (±0.287) and 12.15 mm (±0.105), respectively. The mean shell lengths of the 2005 cohorts in the LVBH, CBM-2, KLM and LMM samples were 17.5 mm (n = 1), 18.9 mm (n = 4), 21.2 mm (n = 1) and 20.1 mm (n = 4), respectively. The occurrence of the 2005 cohort in all four sampled sites suggested that quagga mussel introduction to the Boulder Basin occurred prior to 2005. This supposition is based on the very low probability of individuals from a localized initial introduction appearing in the samples. It is hypothesized that a reproducing quagga mussel population must have been established somewhere in the Boulder Basin by 2003 or 2004 in order to generate enough veliger larvae to settle as relatively wide-spread members of the 2005 cohort and be transported downstream to establish a 2005 cohort at KLM in lower Lake Mohave. Essentially equivalent population structures at all three sampled sites makes speculation on the original site of quagga mussel introduction to the Boulder Basin difficult.

Estimation of carrying capacity for bivalves is generally carried out for mussel culture systems wherein maximizing mussel numbers requires the consideration of both ecological and economic endpoints. We adapted an existing culture-system model to estimate potential carrying capacity of an invasive species, the quagga mussel (Dreissena rostriformis bugensis) in the Boulder Basin of Lake Mead, Nevada. We parameterized the model using both field measurements and known quantities previously published in the literature. To make this model most useful to ecologists and managers, we provide a detailed description and derivation, as well as an example calculation for the model. The model is based on mean Chlorophyll a concentrations in the Boulder Basin of Lake Mead, and the number of quagga mussels needed to filter a given reduction in food particles from the water column. Estimates ranged from a total of 1.51 × 10¹² mussels with a net reduction of 50% of food particles to 1.02 × 10¹³ mussels when the net reduction was at the threshold level of survival (0.017 μg/L). Limitations to the model and potential environmental and ecological considerations are discussed.

Environmental factors that can affect the settlement rate of quagga mussel veligers include flow velocity, water temperature, pH, dissolved oxygen (DO), conductivity, total organic carbon (TOC), and the surface roughness of monitoring substrates. In the present study, six artificial substrates, Acrylonitrile Butadiene Styrene (ABS) plastic, High Density Polyethylene (HDPE) plastic, Concrete Underlayment Board (CUB), aluminum, stainless steel and fiberglass, were used to monitor the settlement of quagga mussel veligers at different water depths in Lake Mead, Nevada-Arizona, USA. Considering the hierarchical data structure of observed mussel densities, we investigated the relationship between mussel settlement on monitoring substrates and the surrounding environmental variables by applying the Linear Mixed Effects (LME) model. After normalization, the above six environmental variables were considered as independent factors in fixed-effect calculation, while water depth and substrate roughness acted as the group variable and the random term, respectively. The results indicated that flow velocity, water temperature, and DO were significant factors in determining the mussel settlement on substrates. TOC was barely significant while conductivity and pH had no impact on settlement of quagga mussel veligers. As to the random effect, no preference for substrate type could be found, while water depth caused considerably more variation in modeling since it might correlate with most environmental variables. There is need to emphasize the critical role of flow velocity which is often ignored by biologists - higher flow velocities significantly decreased the settlement of quagga mussel veligers on substrates. Therefore, to more efficiently monitor quagga mussel colonization in water bodies, artificial substrates should be deployed in areas without strong flow.

Lake Mead, Nevada is the largest reservoir by volume in the United States, as well as a popular sport fishing destination. In January 2007, the invasive quagga mussel Dreissena rostriformis bugensis (Andrusov, 1897) was discovered in the reservoir and concerns began to arise about potential alterations to the aquatic environment. The Lake Mead sport fishery is reliant on the sustainability of prey species like the threadfin shad [Dorosoma petenense (Günther, 1867)]. This study examined 20-year trends in historic abundance of the threadfin shad, before, and shortly after, the discovery of quagga mussels in the system. Larval shad trawl data collected in Las Vegas Bay and Overton Arm portions of Lake Mead were analyzed in the present study. Two-way analysis of variances showed that the abundance of this prey fish has not changed following quagga mussel invasion (P > 0.05). Post-quagga mussel discovery collections of adult threadfin shad from Las Vegas Bay ranged from 113 to 212 mm total length (TL) (mean = 184 mm; n = 170). Shad from Overton Arm ranged from 131 to 197 mm TL (mean = 150 mm; n = 27). Stomach contents were analyzed. The proportion of cladocerans in stomach contents differed significantly from spring to winter in Las Vegas Bay (P = 0.008); whereas the proportion of copepods did not show statistically relevant differences regarding seasonality (P = 0.562). Initial trends in lower trophic level dynamics in response to quagga mussel invasion has yet to reveal significant effects in Las Vegas Bay or Overton Arm. Long-term monitoring on threadfin shad is needed to evaluate potential impacts from invasive quagga mussels in Lake Mead.

Wildland firefighting equipment moves large volumes of raw water during fire incidents in order to extinguish flames or control fire growth. This water movement may serve as pathways for aquatic invasive organisms to be moved between water bodies and watersheds. The equipment used may become contaminated and serve as vectors for future invasions across large geographic areas. New guidelines used by federal firefighting agencies recommend the application of sanitation solutions using quaternary ammonium compounds for decontaminating wildland fire equipment to prevent the spread of aquatic invasive species that may foul the equipment. While quaternary ammonium compounds have been tested on other aquatic organisms, the effectiveness of such compounds has not been systematically tested on dreissenid mussels. We tested the survival of quagga mussel veligers after exposure to a 3% solution of Sparquat 256^® for 5 and 10 minutes. We assessed survival immediately after treatment and then after 60 minutes in fresh water. We found that a 5 minute exposure duration was insufficient to kill 100% of tested veligers. However a 10 minute exposure, as prescribed in the interagency operational guidelines for preventing spread of aquatic invasive species, was effective in killing all tested veligers, but not immediately after treatment. An additional 60 minutes were required after the quaternary ammonium solution was removed before 100% mortality was achieved. This work highlights the need for more rigorous evaluation of the effectiveness of various sanitation solutions in killing quagga and zebra mussels under different ambient temperatures in order to validate and refine the sanitation protocol for firefighting equipment and other applications.

After successfully occupying the benthos of all the Laurentian Great Lakes and connecting channels, quagga mussels [Dreissena rostriformis bugensis (Andrusov, 1897)] have been colonizing the western United States at a much faster rate. Study findings and management experience in the Great Lakes will benefit the water resource managers in the western United States and help them be better prepared to act quickly and effectively to mitigate mussel impacts. We investigated the impacts of dreissenid mussels on nutrients and plankton using a two-dimensional Ecological model of Lake Erie (EcoLE), and compared their impacts with those of mesozooplankters. Model results showed that in the shallow western basin, mussel daily grazing impact was less than 10% of the combined Non-Diatom Edible Algae (NDEA) and diatom biomass, although they cleared a volume equivalent to 20% of the water column daily. Moreover, in the deep central and eastern basins, dreissenids grazed only 1-2% of the NDEA and diatom biomass per day. The relative importance of dreissenids’ grazing impact on diatoms and NDEA to those of zooplankton’s varied among years and basins in Lake Erie. In general, zooplankton had slightly higher grazing impacts than did the mussels on NDEA and diatoms in the western basin but much higher grazing impacts in the central basin. Dreissenid mussels excreted a big portion of phosphorus in the bottom water, especially in the western basin, while zooplankton kept a big portion of algal phosphorus in the water column, especially in the central and eastern basins. Non-Diatom Inedible Algae (NDIA) abundance increased with more phosphorus available and was less responsive to mussel selective grazing. Dreissenid mussels affected crustacean zooplankton mainly through their impacts on NDEA. Our results thus indicate that dreissenid mussels have weak direct grazing impacts on algal biomass due to a concentration boundary layer above the mussel bed, while their indirect effects through nutrient excretion have much greater and profound negative impacts on the system. EcoLE is a modification of CE-QUAL-W2, which is frequently applied to western aquatic systems, and we suggest that with this modification, the models can be used to predict dreissenid impacts in western lakes, reservoirs, and rivers in which they may become established.

Following the discovery of quagga mussels in Lake Mead, Nevada-Arizona, USA, a variety of federal, state and regional agencies set up monitoring programs to evaluate and gain information to help minimize the impacts, or potential impacts, of quagga mussels to their facilities and lake ecology. While the agencies have worked closely and shared monitoring data and findings from the beginning of the infestation, there has been no documented comprehensive monitoring program to describe and record the various quagga mussel-related monitoring needs. Ad hoc interagency quagga mussel meeting representatives established an Interagency Monitoring Action Plan (I-MAP), which outlines agency objectives related to quagga mussel monitoring and provides approaches to realize these objectives. I-MAP team members and their respective agencies provide technical, logistical, and financial support in monitoring quagga mussels and their environmental impacts to Lake Mead. The goal of this effort is to develop a long-term, cost-effective, and consistent monitoring plan for quagga mussels in Lake Mead to inform various agencies and to gain efficiencies from shared operations and information. The plan attempts to build upon current monitoring activities and capabilities, identifies the next steps that can occur within existing capabilities and, finally, outlines gaps and areas of future need.

The discovery of quagga mussels (Dreissena rostriformis bugensis) in Lake Mead, Nevada-Arizona, on January 6, 2007 is the first known occurrence of dreissenid species in the western United States. This study developed elements of a cost-effective and standardized quagga mussel-monitoring program for Lake Mead using preliminary data to arrive at statistically based numbers of sampling sites. To represent the abundance of adult/juvenile quagga mussels in Lake Mead’s heterogeneous floor with 95% confidence, a stratified simple random sampling design revealed a requirement of 41 samples from hard substrates (i.e., rocky areas) and 97 samples from soft substrates (i.e., sandy and muddy areas). A simple random sampling design demonstrated that 42 samples from the lake’s water column are necessary to represent veliger abundance with 95% confidence. Other important elements of the sampling program, such as standardization of protocols and processes and suggested data analyses, are discussed. The monitoring program, which is based on reconnaissance data, is intended to be optimized with data from its first year’s samples. The sample number-selection approach and the other elements of this plan can be easily implemented by lake managers and can also be adapted to other locations where dreissenid mussel monitoring is needed.

Early detection of dreissenid species in water systems is critically important to maintaining structure and function of dam related structures. If mussels are detected early, facility operators may have approximately three to five years to adjust systems before the population of mussels are large enough to restrict the flow of water, clog pipes, restrict water intakes, affect cooling systems, and impede power generation. However, early detection of dreissenids in water with the current methods has some inherent issues with variability in sampling and reliability with analytical methods which creates management decision dilemmas. Since current control methods of these mussels are very limited in regulated water systems, Reclamation is conducting intensive research. To improve early detection in water systems, Reclamation has developed an analytical strategy that includes cross polarized light microscopy, scanning electron microscopy (SEM), flow cell cytometry, and polymerase chain reaction (PCR). This analytical strategy is used on water samples collected using a plankton tow net to collect primarily from reservoirs and also from water flow within facilities, usually from a tap or pipe.

The 100th Meridian Initiative was developed to help prevent the spread of aquatic nuisance species (ANS) through boater education and research on boater movement patterns and behaviors. Surveys employing these elements were conducted at Lake Mead National Recreation Area (LMNRA) in 2002-2003 before the discovery of the quagga mussel (Dreissena rostiformis bugensis Andrusov 1897) and in 2007-2008 after an established population of quagga mussels was found in the Lake. Boaters were asked questions in a personal interview or a mail-in survey regarding what body of water they had previously launched their watercraft in, where they were planning to launch next, if they cleaned their watercraft between each launch, and if they were aware of quagga mussels or other ANS. Results from the personal interviews and mail-in surveys indicated a significant increase in mussel awareness between the pre- and post- mussel invasion groups. Cleaning habits between the study periods for both interviews and mail-in surveys did not differ significantly. Boat trailer states of registration were also documented in both study periods in the parking lots of LMNRA. In 2002-2003, 0.6% of the trailers documented were from states with known zebra or quagga mussel populations, whereas in 2007-2008, 98.2% of states documented had known zebra or quagga mussel populations. Increased boater awareness will help prevent the spread of aquatic invasive species and the 100th Meridian Initiative is a helpful way to educate boaters and collect relevant data on future mussel invasions. The preservation of natural waters is vital for the conservation of native species and the prevention of zebra and quagga mussel invasions will assist in this preservation. Further efforts should be directed toward educating boaters on effective cleaning methods.