Wai Hing Wong

Susceptibility of quagga mussels (Dreissena rostriformis bugensis) to hot-water sprays as a means of watercraft decontamination.

The recent spread of dreissenid mussels to various bodies of water in the western US has sparked interest by many state and federal agencies to develop protocols to stop further expansion. Quagga mussels (Dreissena rostriformis bugensis) are of particular importance as they are currently the most widespread dreissenid species in the region. This project examined the susceptibility of quagga mussels to hot-water sprays at different temperatures and durations of spray contact at Lake Mead (Nevada-Arizona, USA). Emersed adult quagga mussels were exposed to hot-water sprays at 20, 40, 50, 54, 60, 70, and 80°C for 1, 2, 5, 10, 20, 40, 80, and 160 s. Sprays at ≥60°C for 5 s were shown to be 100% lethal. Sprays of 54°C for 10 s, 50°C for 20 s, and 40°C for 40 s also resulted in 100% mortality. A spray temperature of 60°C for 5 s is recommended for mitigating fouling by quagga mussels.

VELIGERS OF INVASIVE QUAGGA MUSSELS (DREISSENA ROSTRIFORMIS BUGENSIS, ANDRUSOV 1897) IN LAKE MEAD, NEVADA-ARIZONA

ABSTRACT The planktonic veligers of the invasive quagga mussel were present year-round from April 2008 to March 2009 in Lake Mead, with high abundance from September to October (>20 veligers/L), whereas the percentage of competent veligers, in terms of the ability to settle, peaked from November 2008 to January 2009 (>60%). The results from this experiment are useful in understanding the life history and population dynamics of quagga mussels in the lower Colorado River Basin.

Potential ecological consequences of invasion of the quagga mussel (Dreissena bugensis) into Lake Mead, Nevada–Arizona

Abstract The recent invasion of the quagga mussel (Dreissena bugensis) in Lake Mead, Nevada–Arizona, USA has the potential to alter biological relationships in this western reservoir. We evaluated the potential impacts by examining several measurements in the Boulder Basin of Lake Mead after the introduction of quagga mussel (2007–2008). Analysis of variance did not reveal any basin-wide changes in chlorophyll a concentrations or water clarity (Secchi disk depth). Although significantly lower chlorophyll a concentrations were found in the outer basin, this reduction was likely related to the decline of dissolved phosphorus concentrations. The abundance of cladocerans, copepods or rotifers has not changed since 2007. Overall, the results suggest that there are no statistically significant changes to many of the standard water quality indices routinely measured in the Boulder Basin of Lake Mead; however, given the complexity of biological, chemical and physical processes driving this ecosystem, the long-term impacts of quagga mussels remain uncertain. This manuscript identifies impacts known to be altered by quagga and zebra mussels in other systems and aims to help lake managers develop experimental and monitoring programs that will accurately address the impacts of quagga mussels.

Early invasion population structure of quagga mussel and associated benthic invertebrate community composition on soft sediment in a large reservoir

Abstract In 2007 an invasive dreissenid mussel species, Dreissena bugensis (quagga mussel), was discovered in Lake Mead reservoir (AZ–NV). Within 2 years, adult populations have spread throughout the lake and are not only colonizing hard substrates, but also establishing in soft sediments at depths ranging from 1 to >100 m. Dreissena bugensis size class and population density distribution differs between basins; cluster analysis revealed 5 adult cohorts within Boulder Basin and Overton Arm but low densities and low cohort survival in the Las Vegas Basin. Regression analysis suggests depth and temperature are not primary controllers of D. bugensis density in Lake Mead, indicating other factors such as sediment type, food availability or other resource competition may be important. Monthly veliger tows showed at least 2 major spawning events per year, with continuous presence of veligers in the water column. Adult mussels have been found in spawn or post-spawn condition in soft sediments in shallow to deep waters (>80 m) indicating the potential for reproduction at multiple depths. Comparisons to a 1986 benthic survey suggest there have been shifts in nondreissenid macroinvertebrate composition; however, it is unclear if this is due to D. bugensis presence. Current distribution of nondreissenid macroinvertebrates is heterogeneous in all 3 basins, and their biodiversity decreased when D. bugensis density was 2500/m2 or greater.

Effectiveness of EarthTec® for killing invasive quagga mussels (Dreissena rostriformis bugensis) and preventing their colonization in the Western United States

Quagga mussels (Dreissena rostriformis bugensis) have created economic and ecological impacts in the western United States since their discovery in 2007. This study focuses on chemical control for preventing the spread of these mussels. The effectiveness of EarthTec® in killing quagga mussels (adults, juveniles, and veligers) in Lake Mead, Nevada-Arizona, was evaluated over time across six concentrations: 0, 1, 5, 10, 17, and 83 ppm. One hundred percent mortality of adult and juvenile mussels was achieved after 96 h with 17 ppm and 5 ppm (respectively), and 100% veliger mortality occurred within 30 min at 3 ppm. From December 2010 to February 2011, the effectiveness of EarthTec® in preventing veliger colonization was also evaluated and the results showed that 2.8 ppm was effective in preventing veliger colonization on fiberglass panels. This study indicates that EarthTec® has the potential to be an effective control agent against the invasive quagga mussel, and more specifically, in preventing the colonization of veligers.

An evaluation of artificial substrates for monitoring the quagga mussel (Dreissena bugensis) in Lake Mead, NV

Abstract This experiment was conducted to determine if quagga mussels (Dreissena bugensis) settle and grow on different types of artificial substrates preferentially in Lake Mead, Nevada–Arizona, one of the first known populations of the mussel in the western United States. Six substrates, acrylonitrile butadiene styrene (ABS) plastic, high density polyethylene (HDPE) plastic, concrete underlayment board (CUB), aluminum, stainless steel and fiberglass were cut into 10 cm squares and placed at different depths in the Boulder Basin of Lake Mead for approximately 1 yr in a modified randomized block design. Half the substrates were removed and replaced every 2 mo, and the other half remained in the water for the duration of the study. No preference for substrate type could be determined, but settlement was limited by depth. Mussel settlement on substrates at depths from 6–28 m was significantly greater than on substrates from 32–54 m (F = 5.54; p < 0.001). This divergence in settlement at different depths is likely due to the water quality characteristics at these depths. No relationship was found between mussel settlement on substrates and veliger concentrations in the water column. Mussel settlement was limited when the lake was destratified between January and March 2009. Based on this experiment, materials placed in Lake Mead below 32 m will have greatly reduced mussel settlement, especially if deployed when the lake is destratified.