Zebra Mussel Monitoring Program

Zebra mussels (Dreissena polymorpha) were first found in Texas in Lake Texoma (on the Texas/Oklahoma border) in 2009 and have since established populations in 14 other reservoirs in Texas. Current (2019) data indicate daily mean water temperatures of more than 30°C negatively affect zebra mussel survival and reproduction. However, zebra mussel populations at lower latitudes could show enhanced tolerance to higher temperatures when compared to populations at higher latitudes, such as Michigan and New York. Compared to zebra mussel populations at higher latitudes, less is known about the effects of water temperatures during winter on zebra mussel populations at lower latitudes. Daily mean water temperatures during winters at Lake Texoma (2011–2019) and two additional reservoirs in north Texas were grouped into three categories: the number of days when the daily mean temperature was (1) less than 12°C, (2) less than 10°C, and (3) less than 8°C. These temperature data were analyzed along with biological data from the USGS Zebra Mussel Monitoring Program for Texas to determine if winter temperature regimes in the three reservoirs affected zebra mussel reproductive success during subsequent spawning events in spring. There were statistically significant correlations between the duration and severity of cold-water temperatures during winter and peak veliger densities observed during the following spring. These results indicate the potential for winter temperature regimes to influence zebra mussel population dynamics at lower latitudes.

Zebra mussels (Dreissena polymorpha) are invasive freshwater bivalves that were first detected in Texas in 2009 in Lake Texoma on the Texas–Oklahoma border. From 2009 to 2015, zebra mussels spread farther into Texas and were detected in four major river basins: Red, Trinity, Brazos, and Sabine. As of May 2016, there are established populations of zebra mussels in five Texas reservoirs, four of which are in north-central Texas. Long-term datasets from three of the north-central Texas reservoirs (Lake Texoma, Ray Roberts Lake, and Lake Lewisville) were analyzed to understand how extreme climate events (drought and flood) affected population dynamics. These datasets included the drought of 2011–2014 and the flood of 2015, which were each followed by population crashes of zebra mussels. Each extreme climate event increased variability of lake levels, which desiccated mussels in littoral zones. However, zebra mussels continued to spread to new water bodies in Texas despite population crashes that occurred during extreme climate events.

Zebra mussels (Dreissena polymorpha) were first detected in Ray Roberts Lake, an impoundment on the Elm Fork Trinity River in north-central Texas, in July 2012. Discharge from Ray Roberts Lake flows 28 km south into the north end of Lake Lewisville, which is the second impoundment on the Elm Fork Trinity River. Zebra mussels were first found in Lake Lewisville on artificial substrates on the south end of the reservoir near the dam, 16 km south of the Elm Fork inflow, in June 2013. About five months later, veligers were detected in the reservoir near the Elm Fork inflow. Detection of different life stages of zebra mussels at distal ends of the reservoir during different timeframes supports the hypothesis that Lake Lewisville was inoculated by separate overland and downstream introduction events on the south and north sides of the reservoir, respectively. Holistic, lakewide monitoring was essential in discerning these introduction events and could assist decision makers when considering implementation of rapid-response plans.

Zebra mussels (Dreissena polymorpha) are invasive freshwater bivalves that were first detected in Texas in 2009. This species is currently (2015) established in five Texas reservoirs. The dispersal of zebra mussels throughout an infested lake or reservoir can be rapid and has been studied in many water bodies in northern latitudes. However, much less is known about the effects of flow conditions on the dispersal capabilities of this species through municipal water transfer pipelines and through combined lake/stream source waters in lower latitudes. The north central Texas region experienced a drought of record (2011-2014) followed by a record-breaking flood (May 2015). Many reservoirs in the upper Trinity River Basin reached record high levels and, subsequently, rivers throughout the basin transitioned from baseflow conditions to combined controlled/uncontrolled reservoir releases. Long-term datasets were analyzed to understand how reservoir levels and flow condition dynamics affect the dispersal of invasive zebra mussels through water transfer pipelines and source water systems.

Zebra mussels (Dreissena polymorpha) are invasive freshwater bivalves that were first detected in Texas in 2009. This species is established currently in five Texas reservoirs. The dispersal of zebra mussels throughout an infested lake or reservoir can be rapid and has been studied in many water bodies in northern latitudes. However, much less is known about the effects of flow conditions on the dispersal capabilities of this species through municipal water transfer pipelines and through combined lake/stream source waters in lower latitudes. The north central Texas region experienced a drought of record followed shortly by a record-breaking flood. Many reservoirs in the upper Trinity River Basin reached record high levels and, subsequently, rivers throughout the basin shifted from baseflow conditions to combined controlled/uncontrolled reservoir releases. Long-term datasets were analyzed to understand how reservoir levels and flow condition dynamics affect the dispersal of invasive zebra mussels through water transfer pipelines and source water systems.

Zebra mussels were first observed in Texas (Lake Texoma) in 2009. The north Texas region marks the current southern extent of the central North American range of this species. Lake Texoma contains some of the warmest reservoir waters inhabited by Dreissena polymorpha (34.3 °C in 2011) and experiences summertime cyanobacterial blooms which can be exacerbated by zebra mussels. Immediate effects of infestation included cessation of interbasin water transfer from Lake Texoma (Red River) to the Trinity River watershed. This transfer comprised 28% of the total water supply for a water district which services 1.6 million residents. A regional monitoring program was developed to assess zebra mussel distribution and population dynamics in nine reservoirs and several lotic systems. Data collected at Lake Texoma during the first three years of the program (2010–2012) were analyzed to determine if zebra mussel population dynamics were related to physicochemical water properties. Veliger densities were related to water temperature, dissolved oxygen, pH, lake levels, and water transparency. Annual veliger density maximum declined significantly suggesting a population crash. In 2011, lake elevation declined to the lowest level recorded during the last 18 years, desiccating a substantial number of settled mussels. Two annual spawning events were observed in 2010 and 2012. Spatial distributions of veligers were related to physicochemical stratification characteristics as veligers moved to the deepest oxygenated water following lake stratification. Although the future geographic range is uncertain, environmental factors likely will affect establishment and reproduction dynamics as zebra mussels spread farther into the southwest United States.

The future geographic range of zebra mussels in North America is uncertain. It is likely that environmental conditions that are outside physiological tolerances of this invasive species will limit spread. In the south and southwest U.S., summertime temperatures often exceed upper thermal tolerances of this species. Temperature and other environmental factors, including calcium, dissolved oxygen, pH, and chlorophyll could affect establishment and persistence of zebra mussels by mediating survivorship and growth of young of the year (YOY) organisms. The current study assessed the effects of environmental conditions on survivorship and shell and body mass growth of YOY zebra mussels in Lake Texoma, a eutrophic reservoir located on the Texas-Oklahoma border. Lake Texoma is composed of two major disjunct inflows, the Red and Washita Rivers. These rivers are quite distinct in water quality characteristics and create gradients of several key environmental variables throughout the reservoir. Cumulative shell and body mass growth was greatest near the two inflows (highest temperatures and chlorophyll concentrations) while survivorship appeared to have no spatial pattern. Daily shell growth maxima were observed mid-way through the 70-day experiment shortly following a decrease in water temperature. Shell and body mass growth followed a curvilinear relationship through time while mortality generally declined. Mussels tended to develop shell before increasing in mass as daily mass growth maxima were observed near the end of the experiment. Nearly all mussels attained sexual maturity prior to spawning in autumn.