ABSTRACT
ABSTRACT Invasive quagga (Dreissena rostriformis bugensis) and zebra (Dreissena ploymorpha) mussels have rapidly spread throughout North America. Understanding the relationships between environmentalvariables and quagga mussels during the early stages of invasion (2-4 years after detection) will bene‘t management strategies and allow researchers to predict patterns of future invasions. Quagga mussels were detected in Lake Mead, Nevada, and Arizona in 2007. We monitored the early invasion of mussels in the soft sediment of Lake Mead; this was done at three speci‘c basins (Boulder Basin, Las Vegas Bay, and Overton Arm) and lake wide (average of all basins) biannually from 2008 to 2011. Mean densities of mussels increased during the ‘rst year of monitoring and stabilized during the subsequent 2 years on the whole-lake scale (geometric minimum and maximum means =8-132 individuals ·m−2), and in two individual basins, Boulder Basin (73-875 individuals ·m−2) and Overton Arm (2-126 individuals ·m−2). In Las Vegas Bay, mean mussels densities ranged between 9 and 44 individuals · m−2, signi‘cantly lower than the other basins. Low densities in Las Vegas Bay were correlated with high sedimentconcentrations of metal and warmer (greater than 30°C) water temperatures. Carbon content in sediments increased with depth in Lake Mead, and during some sampling periods, quagga density was also positively correlated with depth, but more research is required to determine the signi‘cance of this interaction. Laboratory growth experiments suggested that food quantity may limit mussel growth in
Introduction .............................................................................................................................................. 34 Study Site ................................................................................................................................................. 35 Methods .................................................................................................................................................... 36
Sampling ............................................................................................................................................. 36 Sediments ............................................................................................................................................ 37 Mussel Growth Rates .......................................................................................................................... 37 Analysis .............................................................................................................................................. 39
Results ...................................................................................................................................................... 39 PopulationTrends ............................................................................................................................... 39 SedimentAnalysis ............................................................................................................................... 39 Growth Rates ...................................................................................................................................... 43
Discussion ................................................................................................................................................ 44 Mussel Densities ................................................................................................................................. 44 Mussel Growth Rates .......................................................................................................................... 47 Conclusions ......................................................................................................................................... 47
Acknowledgments .................................................................................................................................... 48 References ................................................................................................................................................ 48
Boulder Basin, which may indicate an opportunity for population expansion if primary productivity were to increase. Overall quagga mussel density in Lake Mead was highly variable and patchy, which suggests temperature, sediment size, sediment metal concentrations, and sediment carbon content contribute to mussel distribution patterns.
