Filtration and growth rate of Lake Mead Quagga Mussels (Dreissena bugensis) in laboratory studies and analyses of bioaccumulation.

摘要

In January of 2007, Quagga Mussels (Dreissena bugensis) were identified in Lake Mead, Nevada. An aquatic invasive species, these mussels can significantly alter ecosystems. This study sought to quantify three ecological traits of the species through a series of laboratory experiments and analyses, providing information both for comparison with Dreissena in other locations, as well as for limnologic management decisions. Filtration rate of quagga mussels was quantified using algal strains and natural seston. Two strains of green algae, Nannochloris and Scenedesmus were used to determine mussel filtration rates with a spectrophotometer. Quagga filtration rates of collected Lake Mead seston were determined with a turbidity meter. All clearance rate studies included both a large and small mussel size class, with maximum filtration rates for small mussels from 1167 mL/ g dry mussel/hr for algae, and 496 mL/g dry mussel/hr for large mussels filtering algae. Ecologically related to the clearance rate, the growth rate of quagga mussels was also quantified during a 32 day trial in Lake Mead (Lake) water and also in lake water supplemented with the above mentioned algae strains, illustrating potentially higher growth rates than currently occur in Lake Mead could be possible depending on lake algae levels. Mussel growth was 0.35 day-1 in natural seston, and 1.42 day-1 in supplemented lake water. Implications of mussel growth and filtration led to the study of quagga mussels' potential for concentration of trace elements of concern in the tissue, and feces and pseudofeces of mussels. The contaminant levels in these biological samples were compared to sediment samples from both Boulder Beach at Lake Mead and from the Las Vegas Wash, a potential source of contaminants that flows into Lake Mead. All samples were processed via EPA Method 3050B and elemental analysis was completed with ICP-OES. While a large spectrum of elements were investigated, elements of concern in which statistically higher levels were observed in mussel tissue or pseudofeces and feces over sediment from the adjacent location included arsenic, molybdenum, lead, and selenium. Based on the results, it can be concluded that quagga mussels filter more when smaller in size and still growing, and they filter more when exposed to lower quality foods, and could potentially grow and expand their population impact if lake parameters change. Contaminant data illustrated that for selenium and arsenic bioaccumulation is appearing in mussel tissue, while for lead and molybdenum bioaccumulation is occurring in mussel excretions, potentially leading to changes in benthic composition. Future research studying assimilation, particle filtration, and the impact of seasonal and climate changes on filtration and concentration rates would be valuable for determining the mass balance impact of this species on aquatic environments in the Southwest.