The 100th Meridian Initiative at the Lake Mead National Recreation Area, NV, USA: Differences between boater behaviors before and after a quagga mussel, Driessena rostiformis bugensis, invasion

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

Substrate Monitoring, Contaminant Monitoring, and Educational Outreach on Quagga Mussels (Dreissena bugensis) in Lake Mead, Nevada

The invasive species, the quagga mussel, Dreissena bugensis, was found in Lake Mead, Nevada-Arizona, USA on January 6, 2007. Since then, researchers have been attempting to quantify the amount of damage these mussels will cause to the lower Colorado River basin. Three projects were implemented in this thesis to research the quagga mussel in Lake Mead. First, a study to determine which types of substrates quagga mussels will grow on preferentially was conducted. Six different substrates, Acrylonitrile Butadiene Styrene (ABS) plastic, High Density Polyethylene (HDPE) plastic, Concrete Underlayment Board (CUB), aluminum, stainless steel and fiberglass, were placed in the Boulder Basin of Lake Mead for approximately one year in a modified randomized block design. Half of the substrates were removed and replaced every two months, and the other half remained in the water for the duration of the study (one year). Mussels had no preference in substrate type, but settlement was limited by depth. Mussel settlement on substrates at depths from 6-28 m was significantly greater than on substrates from 32-54 m. This divergence in depth preference is likely due to the different water quality characteristics at these depths. The second study was conducted to determine concentrations of mercury in quagga mussel soft tissue from Lakes Mead and Mohave. The range of mercury concentrations in mussel tissues was 0.017 -0.074 µg/g dry weight. The final project was designed to educate the public and determine certain characteristics of boaters that utilize Lake Mead. Boaters were asked questions about where their next boating destination would be, if they were aware of quagga mussels and if they cleaned their boat between launchings. Of 236 people interviewed, 81% were aware of quagga mussels, but this number needs to increase. To prevent the spread of mussels to other bodies of water, boater education and awareness is vitally important

Abundance and size of quagga mussels (Dreissena bugensis) veligers in Lake Mead, Nevada-Arizona

The planktonic veligers of the invasive quagga mussel were present year-round from April 2008 to March 2009 in Lake Mead, with high abundance from September to October (\u3e20 veligers/L), whereas the percentage of competent veligers, in terms of the ability to settle, peaked from November 2008 to January 2009 (\u3e60%). The results from this experiment are useful in understanding the life history and population dynamics of quagga mussels in the lower Colorado River Basin

Environmental factors affecting settlement of quagga mussel (Dreissena rostriformis bugensis) veligers in Lake Mead, Nevada-Arizona, USA

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

Ecological Consequences of Invasion of the Quagga Mussel (Dreissena bugensis Andrusov 1897) into Lake Mead

Consequences of Invasion of the Quagga Mussel into Lake Mea

FATE, TRANSPORT, AND MIXTURE TOXICITY OF TRANSGENIC BACILLUS THURINGIENSIS CORN (ZEA MAYS) AND ASSOCIATED INSECTICIDES

Corn is a dominating feature in the landscape of the Midwestern United States. Associated with this crop are a plethora of products from fertilizers to pesticides that help farmers maximize grain yield while minimizing costs. A widely accepted form of protection from major pests in the United States is genetically modified corn that has been altered so that it contains genetic material from another species, a soil bacterium, Bacillus thuringiensis Berliner (Bt corn), in order to produce proteins that are toxic to some insect pests. Additional insecticides that are commonly used to protect corn include a neonicotinoid seed coating, clothianidin, and a pyrethroid insecticide applied in-furrow, tefluthrin. The goal of my dissertation was to measure the environmental fate of the Cry1Ab Bt corn protein, clothianidin, and tefluthrin and determine if measured concentrations could be causing effects to non-target species. The Cry1Ab proteins persisted only during the corn growing season in soil, runoff water and sediment with the highest concentrations measured during pollination. Clothianidin was detected in all matrices and remained persistent throughout the year in soil pore water. Tefluthrin was consistently detected in soil, runoff water, and runoff sediment during the corn growing season, but was not found in groundwater or soil pore water. No acute toxicity was observed to any species when exposed to the Cry1Ab protein in corn plant leaf tissue, therefore little risk was anticipated. Non-target species exposed to clothianidin resulted in limited ecological risk from field exposures. Tefluthrin results indicated elevated risk for non-target species exposed to tefluthrin at concentrations that were measured in the field study. There was no increase in toxicity to tefluthrin when non-target species were exposed to a combination of all three insecticides. In summary, the genetically modified corn insecticidal proteins and clothianidin were not found at environmental concentrations exceeding benchmark values for ecological effects, but tefluthrin was consistently detected in the environment at levels that could be causing toxicity to non-target species, especially if it is able to travel off-site

Mercury Concentrations in Quagga Mussels, Dreissena bugensis, from Lakes Mead, Mohave and Havasu

The recent invasion of the Dressenid species, the quagga mussel, Dreissena bugensis, into Lakes Mead, Mohave and Havasu has raised questions about their ability to alter contaminant cycling. Mussels were collected from 25 locations in the three lakes. The overall average was 0.036 ± 0.016 μg g−1 Hg dry wt. The range of the three lakes was from 0.014–0.093 μg g−1 Hg dry wt. There were no significant differences in mercury concentrations among the three lakes (F = 0.07; p = 0.794). From this baseline data of contaminants in quagga mussels from the lower Colorado River, this species may be used to biomonitor lake health

An evaluation of artificial substrates for monitoring the quagga mussel (Dreissena bugensis) in Lake Mead, NV

This experiment was conducted to determine if quagga mussels (Dreissena bugensis) settle and grow on different types of artificial substrates preferentially in Lake Mead, Nevada–Arizona, one of the first known populations of the mussel in the western United States. Six substrates, acrylonitrile butadiene styrene (ABS) plastic, high density polyethylene (HDPE) plastic, concrete underlayment board (CUB), aluminum, stainless steel and fiberglass were cut into 10 cm squares and placed at different depths in the Boulder Basin of Lake Mead for approximately 1 yr in a modified randomized block design. Half the substrates were removed and replaced every 2 mo, and the other half remained in the water for the duration of the study. No preference for substrate type could be determined, but settlement was limited by depth. Mussel settlement on substrates at depths from 6–28 m was significantly greater than on substrates from 32–54 m (F = 5.54; p \u3c 0.001). This divergence in settlement at different depths is likely due to the water quality characteristics at these depths. No relationship was found between mussel settlement on substrates and veliger concentrations in the water column. Mussel settlement was limited when the lake was destratified between January and March 2009. Based on this experiment, materials placed in Lake Mead below 32 m will have greatly reduced mussel settlement, especially if deployed when the lake is destratified

Potential ecological consequences of invasion of the quagga mussel (Dreissena bugensis) into Lake Mead, Nevada–Arizona

The recent invasion of the quagga mussel (Dreissena bugensis) in Lake Mead, Nevada–Arizona, USA has the potential to alter biological relationships in this western reservoir. We evaluated the potential impacts by examining several measurements in the Boulder Basin of Lake Mead after the introduction of quagga mussel (2007–2008). Analysis of variance did not reveal any basin-wide changes in chlorophyll a concentrations or water clarity (Secchi disk depth). Although significantly lower chlorophyll a concentrations were found in the outer basin, this reduction was likely related to the decline of dissolved phosphorus concentrations. The abundance of cladocerans, copepods or rotifers has not changed since 2007. Overall, the results suggest that there are no statistically significant changes to many of the standard water quality indices routinely measured in the Boulder Basin of Lake Mead; however, given the complexity of biological, chemical and physical processes driving this ecosystem, the long-term impacts of quagga mussels remain uncertain. This manuscript identifies impacts known to be altered by quagga and zebra mussels in other systems and aims to help lake managers develop experimental and monitoring programs that will accurately address the impacts of quagga mussels