Montana Field Guide

See StoryMap on Montana's Response to Aquatic Invasive Mussels.

Estimated potential economic damages of Dreissenid mussel infestations in Montana are up to $234 million per year, including $122 million to recreation, $61 million to agriculture, $47 million to infrastructure, and $4 million to government revenue. Additionally, the estimated loss to lake shore property values is estimated to be $497.4 million. See the full report on potential economic costs of Dreissenid mussel infestations in Montana.

The quagga mussel is a small, triangular bivalve (<50mm or ~2 inches) that has a rounded angle, or carina, between the ventral and dorsal shell surfaces. Color patterns vary widely with black, cream, or white bands; a distinct quagga morph has been found that is pale or completely white in Lake Erie (Marsden et al. 1996).

Although similar to the zebra mussel (Dreissena polymorpha), the two species can be easily distinguished. When placed on a surface zebra mussels are stable on their flattened underside while quagga mussels, lacking a flat underside, will not sit flat.

Adult quagga mussels are mostly sedentary and spend their lives near the area where they first settled as juveniles and attached their byssal threads. Most dispersal takes place through the veliger stage after fertilization where they will passively travel with wind direction or water currents.

The quagga mussel can inhabit both hard and soft substrates, including sand and mud, down to depths of 130 m and possibly deeper. The maximum density of quagga mussels in Lake Michigan is at 31-50 m (T. Nalepa, pers. comm.)

Quagga mussels are prodigious water filterers, removing substantial amounts of phytoplankton and suspended particulate from the water. As such, their impacts are similar to those of the zebra mussel. By removing the phytoplankton, quaggas in turn decrease the food source for zooplankton, therefore altering the food web. Impacts associated with the filtration of water include increases in water transparency, decreases in mean chlorophyll a concentrations, and accumulation of pseudofeces (Claxton et al. 1998).

Quagga mussels inhabit freshwater rivers, lakes, and reservoirs. In North American populations, they do not tolerate salinities greater than 5 ppt (Spidle et al. 1995). Water temperatures of 28°C begin to cause significant mortality, and 32-35°C are considered lethal for Dreissena species (Antonov and Shkorbatov 1990 as cited in Mills 1996). The depth at which the mussels live varies depending on water temperature. They are not generally found in lakes near shore in shallow water due to wave action. The quagga mussel can inhabit both hard and soft substrates, including sand and mud, down to depths of 130 m and possibly deeper. The maximum density of quagga mussels in Lake Michigan is at 31-50 m (T. Nalepa, pers. comm.)

Eggs are expelled by the females and fertilized by the males outside the body; this process usually occurs in the spring or summer, depending on water temperature. Optimal temperature for spawning is probably similar to the zebra mussel at 14–16°C. Thousands of eggs can be laid in a reproductive cycle and up to one million in a spawning season. Spawning may last longer in waters that are warm throughout the year.

See Key Findings and Recommendations from the Montana Invasive Species Council's Invasive Mussel Science Advisory Panel

See StoryMap on Montana's Response to Aquatic Invasive Mussels.

Estimated potential economic damages of Dreissenid mussel infestations in Montana are up to $234 million per year, including $122 million to recreation, $61 million to agriculture, $47 million to infrastructure, and $4 million to government revenue. Additionally, the estimated loss to lake shore property values is estimated to be $497.4 million. See the full report on potential economic costs of Dreissenid mussel infestations in Montana.

Dreissena species ability to rapidly colonize hard surfaces can cause serious economic problems. These organisms can clog water intake structures, such as pipes and screens, therefore reducing pumping capabilities for irrigation, power and water treatment plants, costing industries, companies, and communities. Recreation-based activities can also be impacted; docks, buoys, boats, and beaches have all been heavily colonized. Quaggas are able to colonize both hard and soft substrata so their negative impacts on native freshwater mussels, invertebrates, industries and recreation are unclear, but may be worse than zebra mussels which tend to colonize just hard substrates.

Contact information for Aquatic Invasive Species personnel:
Montana Fish, Wildlife, and Parks Aquatic Invasive Species staff
Montana Department of Natural Resources and Conservation's Aquatic Invasive Species Grant Program
Montana Invasive Species Council (MISC)
Upper Columbia Conservation Commission (UC3)

Threats to the quagga mussel are minimal, other than reservoir drawdowns and river dewatering which will leave the mussels prone to desiccation. Although a discrepancy exists when comparing temperature tolerance limits of North American and European populations. Water temperatures of 28°C begin to cause significant mortality, and 32-35°C are considered lethal for Dreissena species (Antonov and Shkorbatov 1990 as cited in Mills 1996).