A new paper in Environmental Toxicology and Chemistry, published by Oxford University Press, finds that efforts to eradicate invasive molluscs in Idaho's Snake River may kill off valuable freshwater species.
Dreissenid mussels such as zebra and quagga mussels are invasive aquatic species that disrupt freshwater ecosystems and cause major economic and social damage. In the United States, observers first found Dreissenid mussels in the Great Lakes, likely introduced via international shipping vessels, in 1988. In subsequent decades Dreissenid mussels spread to lakes and rivers throughout the eastern and central United States, causing dramatic shifts in food chains, collapsed fisheries, altered biogeochemistry, decreased dissolved oxygen levels, increased algal blooms, and, from 1989 through 2004, an estimated $267 million in mitigation costs to water treatment and electrical plants.
Much of the western U.S. remains uninfested. But in late 2023, the State of Idaho found larval and adult quagga mussels in the Snake River near Twin Falls, Idaho, the first known occurrence in the Columbia River Basin. To prevent the spread of quagga mussels throughout the basin, Idaho introduced an eradication plan to treat the river with a copper-based molluscicide for 10 days. This molluscicide contains 28.2% copper ethanolamine and 9.1% metallic copper. In total, the state dumped some 46,000 gallons of molluscicide in the river.
People use copper-based chemical treatments to eradicate invasive mussels commonly in small ponds and lakes, but not often in large rivers. Researchers here assessed the transport and fate of the copper and its exposure and effects on the other organisms living downstream in or around the Snake River.
They collected water samples at seven locations throughout the treatment period. While the researchers found that nearly half of the original mass of copper was gone from the water by the end of the observation, dissolved copper concentrations were higher than the toxic limit for more than two weeks after the copper treatment began.
Overall animal abundance decreased from 54% to 94% at the sites the researchers assessed, this was driven by reduced numbers of water nymph worms, flatworms, midge flies, freshwater shrimp, and pebblesnails, Other animals, including the New Zealand mud snail, the gyro snail, and the tadpole snail, disappeared altogether from the river. However, small numbers of new organisms appeared after the treatment, including sludge worms, seed shrimp, and several new insects, including the buffalo gnat.
The apparent effect of the copper on animals and habitats as far as almost 40 miles downstream of the treatment is especially striking and potentially consequential for federally listed threatened or endangered animals living in the area. The change in animal diversity due to the copper treatment has potentially serious implications for the diets and habitats of other animals, including protected fish in the region.
The paper, "Fate and effects to the benthic community of a copper treatment to eradicate invasive mussels in a large western river, USA," is available (at midnight on July 15th) at https://doi.org/10.1093/etojnl/vgaf119 .
Direct correspondence to:
Austin K. Baldwin
Research Hydrologist
U.S. Geological Survey
230 N Collins Rd.
Boise, ID 83702
