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Lake Mead Science Symposium Concurrent Sessions
EMERGING ISSUES
Session Chairs:
Peggy Roefer and Shawn Gerstenberger
Tuesday, January 13, 2009 * 1:15 pm to 5:00 pm * Ballroom1:20 – 1:40 pm
Quagga Mussel Invasion into Lakes Mead and Mohave in 2007: Abundance, Distribution, and Size Frequency
Moore, Bryan-1; Gerstenberger, Shawn-2; and Wong, David-2, (1) NPS Lake Mead NRA (2) University of Nevada, Las VegasOn January 6, 2007, the quagga mussel (Dreissena bugensis) was found in Boulder Basin of Lake Mead. This is the first known occurrence of dreissenid species in the western United States. Upon this emerging issue, the National Park Service started to monitor the population dynamics at different spatial and temporal scales in Lake Mead. Before the end of January, adult mussels were found within all of the Boulder Basin and in the extreme western side of the Virgin Basin. No mussels were found in the Overton Arm, Gregg Basin, and Temple Bar areas. In Lake Mohave, mussels were only found in the southern section below the Cottonwood Basin. By the end of 2007, mussels had been found throughout lakes Mead and Mohave. The density of quagga mussels has been determined at 138 locations in Lake Mead. The average density in year 2007 was 505 ± 667 mussel/m2. There were more mussels in rocky areas than silty areas. The density in both areas increased with depth down to approximately 21 meter where the densities started to decrease as depth increased. From March to August, the density in Stewart Cliffs of Lake Mead increased 3.6 and 5.9 times at depth of 12.2 m and 18.3 m, respectively. Size frequency demonstrated that there were always three to four cohorts for each population with shell length range from less than 1 mm to 25 mm. The growth rate decreased significantly as the mussel size increased, i.e., the larger the mussel, the slower the growth.
1:45 – 2:05 pm
Growth and Recruitment of Quagga Mussels (Dreissena bugensis) in Lake Mead
Baldwin, Wen-1; Mueting, Sara-2; Gerstenberger, Shawn-2; Wong, David-2
(1) NPS Lake Mead National Recreation Area and (2) University of Nevada, Las VegasWith invasion of quagga mussels into Lake Mead, there is a need to investigate their growth and recruitment to monitor their population dynamics. Mussels from 2 to 9 mm in shell length were held individually in a cage in Las Vegas Boat Harbor at 7.5 m from July 31, 2007 to March 19, 2008. The shell length measurements indicate that smaller mussels grew faster than larger ones. It took a mussel 110 days to grow from 2.5 to 10 mm. The maximum shell length was 18.9 mm. Another experiment was conducted based on those cohorts settling on ABS plastic pipes suspended in two lines: seven pipes in Line 1 in shallow water (6.4 - 9.1 m) since November 23, 2007 and eight pipes in Line 2 in deep water (8.2 - 18.6 m) since January 3, 2008. Length frequency was measured during each sampling. There are two major cohorts on each pipe and one of the cohorts was always dominated by the newly settled juveniles (84%). Therefore, the recruitment is very active. The shell length of the populations between these two lines didn’t show significant difference, though the estimated maximum shell length of mussels from Line 1 and Line 2 were estimated to be 16.0 and 11.2 mm, respectively. Mortality was observed when the mussels are around 10 mm or even smaller. The information on population dynamics from this study can be used by lake managers to evaluate their impacts on water quality, food webs, and public facilities.
2:10 – 2:30 pm
The Development of a Suitable Substrate Sampling Device for Monitoring Quagga Mussels (Dreissena bugensis) in Lake Mead, Nevada
Mueting, Sara-1; Gerstenberger, Shawn-1; Wong, David-1; Baldwin, Wen-2; and Urban, Mitch-2, (1) University of Nevada, Las Vegas (2) NPS Lake Mead National Recreation AreaThe discovery of the quagga mussel (Dreissena bugensis) in Lake Mead, Nevada-Arizona has left researchers and lake managers with many daunting tasks related to monitoring the species’ impact on the normal ecology of the lake. This experiment tested the quagga mussel’s preference for substrate types in order to develop a monitoring plan for Lake Mead. Six materials were tested including high density polyethylene (HDPE) white plastic, ABS black plastic, concrete underlayment board (CUB), aluminum, stainless steel and fiberglass. Substrates were cut into 4 inch squares and placed at 5m intervals from 5m to 55m deep in a modified Latin square design in the Boulder Basin of Lake Mead near Sentinel Island. Since May 2008, substrates were removed and replaced with new substrates every two months for a total of four sampling events. All of the materials had mussel colonization, but colonization depended on substrate type and depth. Depths from 10-20 m experienced 4-12 times the number of mussels settled than lower depths. Aluminum and CUB were the preferred choice for mussel settlement, however it was difficult and time consuming to count the number of mussels on CUB, so this is not a recommended substrate for the monitoring plan. Stainless steel plates had smaller mussel counts than other materials. Based on the data presented in this paper, we will propose a monitoring plan for Lake Mead and make suggestions to industries that use Lake Mead water.
2:35 – 2:55 pm
Characterization of the Phytoplankton Communities in the Basins of Lake Mead – Do Quagga Mussels Influence Cyanobacterial Biovolume?
Beaver, John R.-1; Teacher, Catherine E.-1; Blasius-Wert, Becky J.-2; Kirsch, Janet E.-2
(1) BSA Environmental Services, Inc. (2) U.S. Bureau of ReclamationThe phytoplankton communities for 20 stations in the basins of Lake Mead were monitored quarterly from November 2006 through November 2008 coincident with the expansion of quagga mussel populations. Total phytoplankton biovolume in Lake Mead displayed seasonal fluctuations with peak biovolumes in May and August in 2007 and 2008. Total phytoplankton biovolume was strongly correlated with chlorophyta biovolume, however, the late summer total phytoplankton biovolume peaks were driven at many sampling locations by cyanobacterial blooms. Total phytoplankton biovolume was strongly correlated with chlorophyll a concentrations but the correlation between cyanobacterial biovolume levels and chlorophyll a was weak, suggesting that species level algal identification is necessary to monitor potentially harmful cyanobacterial blooms.
Quagga mussel veliger biomass was positively correlated with cyanobacterial biovolume at some stations in Boulder Basin. Increased cyanobacterial levels, specifically Microcystis, have been documented in other lakes where invasive mussels have been established for longer periods of time. Monitoring Microcystis is especially important due to potential toxicity and may cause taste and odor problems with drinking water. Based on the progression of mussel infestations in other systems, a potential expectation over time is that the biovolume of cyanobacteria (e.g., Microcystis) and heterotrophic bacteria will increase in importance in the water column. Using veliger abundance as a surrogate of quagga success, some regions of Lake Mead are approaching concentrations of mussels found in the Great Lakes where the Microcystis events/shifts have occurred.
3:15 – 3:35 pm
Potential Ecological Consequences of Invasion of the Quagga Mussel (Dreissena bugensis Andrusov 1897) into Lake Mead
Wong, David-1; Tietjen, Todd-2; Gerstenberger, Shawn-1; Mueting, Sara-1; and Loomis, Eric-1, (1) University of Nevada, Las Vegas (2) Southern Nevada Water Authority
The invasion of Lake Mead by quagga mussels has the potential to change the ecosystem as impacts are propagated through the system. With increases in abundance and distribution, quagga mussels can transfer particulate matter from the water to benthic environments efficiently. Concentrations of chlorophyll will likely decrease and phytoplankton composition will shift as grazing resistant and benthic forms dominate. Zooplankton biomass will likely decrease because of increased competition and direct consumption on small species by quagga mussels. The Lake Mead fishery may be impacted as sport fish and their prey are limited by the diversion of resources. Some species like the common carp can use quagga mussels as food and may benefit as productivity is diverted to the benthos. Over the long term, nutrient dynamics may be altered by quagga mussel activity as epilimnetic concentrations shift, and as nutrients are buried along with quagga mussel pseudofeces. Water transparency and aquatic macrophytes may increase in areas where phytoplankton and other suspended particles are reduced. Benthic production overall will increase as quagga mussels flourish, but other benthic species may suffer. Oxygen in the hypolimnion will decrease due to respiration by quagga mussels and the bacteria associated with their psuedofeces. The pelagic concentrations of metals and organic pollutants will decrease as quagga mussels accumulate these materials. The magnitude and persistence of these changes will be influenced by a complex combination of the dynamics of the quagga mussels, water level fluctuations, and alterations to discharge and withdrawal characteristics. This manuscript is designed to help lake managers better understand and manage Lake Mead.3:40 – 4:00 pm
The Ecology of Cultural Resources: Issues and Impacts related to Submerged and Emergent Cultural Resources at Lake Mead National Recreation Area
Seeb, Sami K. and Choate, David, NPS Submerged Resources CenterWith many pressing issues affecting the ecological health of Lakes Mead and Mohave, it is easy to overlook the impacts to cultural resources. However, when examined on a more practical level, it becomes clear that one cannot meaningfully address the ecological health of man-made lakes without exploring cultural resources as well. It is human behavior that created the lakes in the first place, and ultimately, it is human behavior that creates the ecological parameters within which impounded rivers develop and evolve. People have inhabited the shores of the historic Colorado River for thousands of years. The submerged and emerging cultural resources within Lake Mead NRA provide tangible evidence of this human interaction with the landscape. Natural impacts initiated and intensified by human behavior are affecting the cultural resources scattered on the lake bottom and surrounding shorelines. Investigating impacts to submerged and emergent cultural resources provides a unique avenue to gain insights that might not be otherwise discovered. Specifically, invasive aquatic species and drought have dramatic effects on the cultural resources within the park and both are at least partly the result of human activity. The quagga mussel infestation is already showing signs of physical damage to submerged cultural resources and research suggests additional unseen impacts to the cultural materials and their surrounding environment. Lowering water levels also result in impacts to cultural resources. Assessing these impacts will facilitate understanding of issues impacting ecological health locally, and on a broader scale, world-wide.
4:05 – 4:25 pm
Will Quagga Mussels Potentially Impact the Native Species’ Food Web in Lake Mead by Affecting Plankton and Nutrient Availability?
Link, Carolyn L.; Acharya, Kumud; and Papelis, Lambis, Desert Research Institute
Zebra and quagga mussels have had extensive ecological impact on the Great Lakes because of their large filtering capacity and high density. By filtering considerable amounts of water they effectively remove plankton biomass from the water column. Subsequent mussel waste increases ammonia levels present benthically and pelagically. Based on experience from the Great Lakes and Mississippi Basin, it is likely that the invasion of the plankton filtering quagga mussels (Dreissena bugensis) into Lake Mead will shift the food web away from native species either by decreasing the plankton biomass or changing nutrient conditions to favor other plankton species. The objectives of this laboratory study focus on quantification of algal clearance rates and ammonia excretion as a function of size of mussels and food concentrations. Prior to study commencement mussels were collected, acclimated to laboratory aquaria, and physically classified. Algal and ammonia concentrations were determined by measuring spectral absorbance and then comparing measurements to a pre-calibrated curve relating absorbance to concentration as determined with a Lachat Quickchem Autoanalyzer. The expected filtration results will aid characterization of the extent quagga mussels may impact Lake Mead’s benthic and pelagic food webs by changing algal biomass and lake clarity.
4:30 – 4:50 pm
Lake Mead Zoobenthos: Changes in Composition, Distribution, and Composition over Time with Emphasis on the Ecology of Adult Quagga Mussel
Chandra, Sudeep-1; Caires, Annie-1; Rosen, Michael-2; Wittmann, Marion-3; Umek, John-1 (1) University of Nevada, Reno (2) U.S. Geological Survey (3) University of California, Davis
The Lake Mead fishery is one of great importance to both sport fisherman and conservationists seeking to protect the native razorback sucker. Previous research suggests the sport fishery is largely driven from benthic production (see Umek et al. presentation, this symposium). However, no quantitative information exists regarding the contemporary composition and production of zoobenthos. This information is even more critical given the recent introduction of invasive quagga mussel to the lake in order to gauge future change and potential opportunities for restoration. In this study, we present the current composition, biomass, and changes in zoobenthic production over two time periods. Also, we briefly review the effect of quagga mussels on other limnetic ecosystems and present findings that describe their current distribution, population size structure, and energetics (pelagic to benthic coupling) with depth.