Invasive mussel found in North America for first time, poses immediate threat in California's delta

Rosanna Xia, Los Angeles Times on Nov 2, 2024

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A particularly-worrisome mussel species has snuck into North America for the first time through the Sacramento-San Joaquin River Delta — sparking what many are calling an immediate threat to California's most significant watersheds.

Golden mussels, an invasive freshwater bivalve that has devastated ecosystems and critical water infrastructure in other parts of the world, were recently discovered near the Port of Stockton. Limnoperna fortunei appear to have also found their way many miles downstream into O'Neill Forebay of the San Luis Reservoir, where officials in Merced County have been rapidly conducting genetic testing.

"The species poses a significant immediate threat to the ecological health of the Delta and all waters of the state, water conveyance systems, infrastructure and water quality," according to a public alert by the California Department of Water Resources and the California Department of Fish and Wildlife. "This discovery is the first known occurrence of golden mussels in North America."

These mussels likely infiltrated California by a ship traveling from an international port and are likely to spread throughout the Delta and through the water infrastructure associated with the Delta, officials said in a statement. "Without containment, golden mussels are likely to spread to other freshwater bodies in California, and to other ports and inland waters of North America, and abroad."

These tiny dark-yellowish mollusks, native to rivers in China and Southeast Asia, have already wreaked havoc in South America and for years, they have kept officials and ecologists across the United States on high alert. In each country where these golden mussels have taken over, the initial introduction also appeared to be from ships biofouling on the hulls and, or from ballast water release.

And in most of these cases elsewhere, the golden mussel's range rapidly expanded up or downstream from the point of introduction — usually at a port and then through local, human-mediated pathways, officials said.

Both a freshwater and brackish species, golden mussels can tolerate wide ranges in salinity, temperature and pH levels, and they can also insidiously travel much farther than you might think. Shortly after fertilization, the larvae become mobile and are capable of coordinated swimming as they disperse in the water column.

Golden mussel takeovers in other countries have shown that this species can grow in stunning clumps or colonies containing as many as 80,000 to 200,000 organisms per square meter.

Wildlife officials have noted that golden mussels can also survive in considerably lower calcium waters than either the quagga or zebra mussel, which have caused quite a few problems across lakes and reservoirs in California, as well as in the Great Lakes region and in many other lakes across the United States.

In addition to disrupting the ecological balance of an entire fresh body of water, golden mussels pose a significant threat to California's water infrastructure. These mussels can clog critical water intakes and fish screens, and also foul major pipes that we rely on for water supply.

Agricultural irrigation and power plant operations could also be significantly impeded, and if past mussel infestations are any indication, golden mussels can also severely impact boating and recreation by encrusting docks, engines and steering equipment.

In California, a team of state, local and federal agencies have been actively monitoring and coordinating their next steps to contain the species from spreading further in California and beyond. Officials have also called upon anyone working and recreating in California lakes and rivers to clean, drain and dry their watercraft and equipment every time it is removed from a body of water. (The California State Parks' Division of Boating and Waterways has a webpage detailing how to "clean, drain and dry" your boat.)

"This simple measure has served to prevent spreading quagga and zebra mussels and is equally effective in stopping the overland spread of golden mussels," officials said.