Invasive Mussels Recently Spotted in California Mark a First for North America

With a name like golden mussels, it may seem like the freshwater bivalve now making headlines in California belongs in the golden state. But the species recently found in the Port of Stockton of the Sacramento–San Joaquin Delta is hundreds of miles away from its native habitat.

“The species poses a significant immediate threat to the ecological health of the Delta and all waters of the state,” officials from the California Department of Fish and Wildlife Service wrote in a statement on Thursday.

Golden mussels, or Limnoperna fortunei, belong in the lakes and rivers of China and Southeast Asia, but can also be found in other non-native waters, like Hong Kong and Taiwan. The invasive mussels form heavy encrustations that could block waterways, as well as harm native species and diminish water quality, the officials write in the statement. Other mussels discovered downstream are undergoing further testing to confirm the species.

For Peter Moyle, a biologist at UC Davis, it might not be possible to get rid of the mussels unless they’re contained and eliminated immediately, he tells CalMatters’ Alastair Bland.

“If we’re lucky, and we stage a real eradication effort in the area where it’s presently found, it might not be too costly and would be worth it,” Moyle tells the outlet.

Before arriving in North America, the species is believed to have invaded South American rivers through ballast water—the fresh or saltwater that is held on ships. In 2021 in Brazil they had invaded about 40 percent of the country’s hydropower plants, according to Science’s Sofia Moutinho in October of that year.

In southern Brazil’s Lake Guaíba, “the golden mussel transformed the lake’s sandy beaches and vegetated margins into piles of dark and stinky shells,” Maria Cristina Dreher Mansur, a biologist at Universidade Federal do Rio Grande do Sul, tells Science.

Experts believe that the mussels may have arrived in North America the same way they did in Brazil and Argentina—through ballast water. For Andrew Cohen, the director of the Center for Research on Aquatic Bioinvasions in Richmond, the mussels' arrival comes as no surprise as ballast water is regularly discharged in the area, he tells CalMatters.

Due to worries about invasive species, the California Natural Resources Agency asks for people to clean, drain and dry boats and equipment every time they’re removed from water. Measures like these have prevented the spread of other invasive species like quagga and zebra mussels, they say in the statement.

This is not the first time the Sacramento–San Joaquin Delta has battled against invasive species. California has spent millions eradicating invasive species like nutria, Atlantic cordgrass and the European green crab. There are at least 185 non-native species living in the Delta, according to the Sacramento-San Joaquin Delta Conservancy, with many more likely to arrive.

Thus, the discovery of the caramel-colored golden mussels in such an affected place comes as no concern to some. “I’ve heard alarms all my life about quagga mussels, zebra mussels, mitten crabs and nutria,” says Brett Baker, an attorney at the Central Delta Water Agency to CalMatters. “I just don’t think there’s enough slack in the system, or enough niche space, particularly for a species that isn’t evolved to live here … I’m pretty sure we won’t be talking about the golden mussel in 20 years, but I could be wrong.”

Alexa Robles-Gil | | READ MORE

Alexa Robles-Gil is a bilingual science journalist based in New York City. Her work has appeared in the Guardian, Undark, Inside Climate News and more.