Invasive mussels

Overview

Figure 1. Quagga mussels in the Central Arizona Project (Image Source: Central Arizona Project Storymap)

Two related species of freshwater mollusks native to Eastern Europe, quagga mussels (Dreissena bugensis) and zebra mussels (Dreissena polymorpha), have become damaging invasive species in much of the United States, including the Colorado River Basin. It is believed that both mussel species arrived in the Great Lakes in the late 1980s when transoceanic vessels inadvertently carried them in ballast water tanks. Both the larvae (veligers) and adult mussels attach themselves to boat hulls, and the spread of mussels within the U.S. has likely occurred when recreational boats are transported from one water body to another.

Attaching themselves to surfaces by the thousands (Figure 1), the invasive mussels clog, biofoul, and otherwise impair water and power infrastructure. Invasive mussels also degrade recreational opportunities in infested water bodies and rivers, can impair propellor use, and lead to time-consuming boat inspections. In the process of filter-feeding, quagga and zebra mussels filter large volumes of water–about 1 liter/day per individual–which disrupts the aquatic food web by decreasing the availability of zooplankton and algae for native species, and increasing water clarity–which, counterintuitively, can contribute to proliferation of aquatic weeds.

Monitoring efforts of invasive mollusks and crustaceans include both counts of adult individuals and eDNA analyses. Reclamation collects water samples from water bodies across the western states, including water bodies in the Colorado River, which are analyzed with microscopy to detect veligers and molecular methods to detect the presence of mussels using eDNA. These monitoring results are collated in the Reclamation RISE database.

Quagga Mussels

Originally from Eastern Europe, the quagga mussel is a small (< 1.5” ) freshwater mollusk with white to yellow coloration. Quagga mussels reproduce prolifically and are difficult to eradicate. Quagga mussels were first found in the Colorado River Basin in 2007 in Lake Mead, Lake Mohave, and Lake Havasu. In 2012, quagga mussels were found in Lake Powell. Quagga mussels now live throughout the Colorado River system below Lake Mead, including the Central Arizona Project and all infrastructure in California receiving raw Colorado River water. There is much concern about quagga mussels spreading in the Upper asin beyond Lake Powell. While self-sustaining populations have so far failed to establish, individual mussels have been found in Lake Granby, Grand Lake, Shadow Mountain Reservoir, Willow Creek Reservoir, Blue Mesa Reservoir, and Green Mountain Reservoir. Quagga mussels have some predators in the Colorado River system such as the Redear sunfish, which lives in parts of the Colorado River basin including Lake Havasu and below Davis Dam. These predators offer both an opportunity for some form of biologic population control and a potential mechanism for toxins and microorganisms found in quagga mussels to move up the food chain.

Zebra Mussels

Similar to the quagga mussel, the zebra mussel is a small (< 2”) freshwater mussel from Eastern Europe, and typically have distinct dark stripes on their shells. ebra mussels have similar habits and deleterious impacts on waterways and infrastructure as the quagga mussel. Unlike the quagga mussel, which is predominantly impacting waterways and water bodies in the Lower Basin, and also Lake Powell, zebra mussels are at present found only in the Upper Basin, in Lake Powell and Highline Lake near Grand Junction. In locations where quagga and zebra mussels co-occur, such as Lake Powell, quagga mussels tend to outcompete zebra mussels and have broader habitats, extending to deeper, colder regions of the lake.

Data and tools

Reclamation RISE Database

Reclamation’s RISE database includes invasive mussel count and monitoring data from reservoirs and river reaches with infestations; enter “mussel” in the search bar.

Additional resources

NPS Glen Canyon Mussel Updates

The Glen Canyon National Recreation Area maintains mussel updates on its website, including current watercraft decontamination strategies and requirements.

Invasive Mussel Collaborative

The Invasive Mussel Collaborative collates ongoing prevention and removal projects across the United States, including several which extend through parts of the Colorado River basin.