Understanding Basin Specific Life History Characteristics of Lake Mead Quagga Mussels (Dreissena bugensis) and a Potential Treatment Using UV Radiation in Laboratory Studies
Creators: name: Thaw, Melissa 
Publisher: name: University of Nevada, Las Vegas
Year: 2013

description: The quagga mussel (Dreissena bugensis) is an aquatic invasive species that is spreading throughout Lake Mead and other western waterways. Unlike their native waters in Eurasia, Lake Mead exhibits year round warm temperatures, high calcium levels and a lack of natural predators, all of which are very favorable conditions for their growth and spread. Dreissena bugensis reproduce and colonize hard surfaces rapidly, where they filter large amounts of water. They disrupt the aquatic food chain and interfere with infrastructure that is exposed to lake water. There is an urgent need to understand Dreissena bugensis life history characteristics within this new habitat to help managers make decisions. Not only does Lake Mead present opportunities for Dreissena bugensis to cause ecological damage, but economic damage to infrastructure is also major concern. Lake Mead is made up of several unique basins, which present unique conditions for Dreissena bugensis and unique challenges to managers. This study sought to characterize Lake Mead basin specific characteristics and respective Dreissena bugensis growth rates in order to shed light on how Dreissena bugensis growth might vary from basin to basin. 
Water quality data was analyzed to characterize two different basins with a focus on nutrients fundamental to the aquatic food chain, including nitrogen (N), phosphorus (P), total organic carbon (TOC) and chlorophyll a. Additionally, Dreissena bugensis growth rates from each of those basins were measured in laboratory experiments. Boulder Basin had significantly higher nutrient levels and Overton Arm had significantly higher chlorophyll a levels. Overton Arm yielded higher Dreissena bugensis somatic growth rates. This adds to our knowledge of how basin specific characteristics may be influencing the interaction between invasive Dreissena bugensis and their recently colonized habitats in a complex reservoir. 
There is a major need for improved methods of treating invasive mussels at Lake Mead and other invaded waterways. The development of non-chemical treatments, such as ultraviolet (UV) radiation, is an important area in need of research because many chemical treatments, such as chlorine, produce harmful byproducts. The first step in developing UV as a potential treatment for Dreissena bugensisis to determine the amount and intensity needed to kill Dreissena bugensis at various life stages. The second part of this study sought to model, through dose-response functions, the quantity of UV needed to obtain high mortality rates of adult, juvenile and veliger Dreissena bugensis. Dreissena bugensis were exposed to different intensities of UV radiation in laboratory experiments. Chronic (long-term) exposure was administered to adult and juvenile mussels, with mortality monitored daily. Veligers were administered acute (short-term) exposure and mortality was observed post-exposure. Dose-response functions were fitted to the resulting data to represent the relationship between the dose (time and intensity) and the resulting mortality. The Lethal Dose-50 (LD<sub>50</sub>), or median lethal dose, is the lethal dose needed for 50% mortality. The LD<sub>50</sub> was calculated from the dose-response functions; the LD<sub>50</sub> values can be used to compare Dreissena bugensis with other species. The quantification of UV needed for high mortality rates in Dreissena bugensis found in this study can be used in engineering applications for treating Dreissena bugensis. The LD<sub>50</sub> values were estimated as 44,000 mJ/cm2, 11,000 mJ/cm2 and 860 mJ/cm2 for adult, juvenile and veliger Dreissena bugensis, respectively.