Survival, growth, and settlement of Dreissena rostriformis bugensis veligers in low and high calcium waters
Creators: name: Ruhmann, Emma 
Publisher: name: University of Nevada, Las Vegas
Year: 2014

description: Populations ofDreissena rostriformis bugensis(quagga mussels) have continued to spread throughout the western United States since their discovery in the Boulder Basin of Lake Mead, NV-AZ in early 2007. Today, quagga mussel specific research is still lacking and the physicochemical characteristics of aquatic systems required by quagga mussels to successfully establish is not fully understood. This includes an absence of research in aquatic environments in the western United States and on quagga mussel veligers (larval stage). Calcium is considered the defining factor for determining if a lake or river is suitable for quagga mussel establishment. The minimum calcium threshold for invasion was developed in prior studies using the calcium requirements of zebra mussels, a close relative to the quagga mussels. Research has shown that there are many differences between the two species and the risk of quagga mussel survival in low calcium waters might be underestimated. This study sought to fill the gaps in quagga mussel veliger research. Three parameters (survival, growth, and settlement) were used to determine their potential effectiveness of establishment in aquatic environments with varying levels of dissolved calcium. To study the potential of veligers to survive, grow, and settle, three bioassays were completed. The first analyzed survival and growth of veligers in two different systems (Lake Mead and Lake Tahoe). Lake Tahoe, CA-NV was chosen as the system to represent naturally low calcium levels (approximately 12 ppm Ca). Quagga mussels have yet to establish in the Lake. To represent a system of high calcium, water from Lake Mead, NV-AZ (approximately 70 ppm Ca) was used. This assay concluded that while veligers raised in the Lake Tahoe water had a lower survival rate than those in the Lake Mead water, those veligers which survived grew at an equal growth rate. The second assay looked at survival and growth with three additional water treatments (Lake Tahoe with Ca amended to approximately 20, 25, and 32 ppm). The added calcium in the Lake Tahoe water helped to increase survival; and again, growth rates among all five treatments were very similar. Both survival and growth assays showed that those veligers which survived the 28 day assay grew at a similar rate no matter the calcium level of the treatment water. The third assay was designed to determine the settlement potential of veligers raised in three different treatment waters (Lake Mead, Lake Tahoe, and Lake Tahoe with 25 ppm Ca). Veliger settlement is an important life event because it indicates that the veligers have found a suitable habitat to remain in and metamorphose into the adult stage. Results indicate that the percent of settlement was improved with increasing levels of calcium. The findings from these assays will aid in aquatic invasive species management. They were designed so that they can be replicated using water from other western lakes with low levels of calcium to test the potential for quagga mussel establishment. Quagga mussels cause both economic and ecological impacts. It is important to better understand them in hopes of preventing their spread to other systems and minimizing their impact on the environment.